Tom's Computer Dictionary

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0.13, 0.18, 0.25, 0.35 micron: see fabrication.

130nm: see fabrication.

1394: See IEEE-1394.

1991: birth year of the World Wide Web. Previously, the Internet was a textual experience.

1G: the first-generation cellular telephony standard, which used analog technology instead of digital technology. Now obsolete.

22nm: a 22-nanometer semiconductor-fabrication technology that began mass production in 2011. See fabrication.

230: shorthand for Section 230 of the Communications Decency Act of 1996 (47 U.S. Code § 230). See Section 230.

24/7: access or uptime that's available 24 hours a day, 7 days a week. This term often refers to the availability of a server or network.

2FA: two-factor authentication. A security measure that augments the usual username and password (the "first factor") required to log into an online account. The second factor may be a temporary second password obtained by a phone call, e-mail, or text message. Some systems require a random number generated by a small device entrusted to the account user.

2G: the second-generation cellular telephony standard, which uses digital instead of analog technology and supports data-transfer rates up to 9.6Kbps.

2.5G: the "two-and-a-half" generation cellular-telephony standard, which uses basically the same digital technology as the 2G standard but increases the data-transfer rate to a maximum 115Kbps.

32nm: a 32-nanometer semiconductor-fabrication technology that began mass production in 2009. See fabrication.

3D printer: a machine that builds three-dimensional objects by heating and bonding raw plastic or resin, although some high-end machines use metal. 3D printing is usually employed for prototypes or small production runs, not for mass production. Some 3D printers are for consumers; others are industrial. All are controlled by computer software with which designers create 3D models of the objects. See ABS, CAD, DLP, FDM, PETG, PLA, SLA, SLS.

3DXP: see 3D XPoint.

3D XPoint: a new nonvolatile memory technology announced by Intel and Micron in 2015. Pronounced "three-dee crosspoint," it was promised to be about 1,000 times faster than flash memory, less expensive than DRAM, and able to withstand more use than flash memory without degrading. "Nonvolatile" means it retains data even when powered off (like flash memory, but unlike DRAM). However, the initial 3DXP products released delivered less performance than promised. See DRAM, flash, volatile, NVMe.

3DES: Triple-DES. See DES.

3DNow!: Introduced in 1998 with AMD's K6-2 processor, 3DNow! originally consisted of 21 new instructions that speed up 3D graphics and other tasks on x86-compatible processors. In late 1999, with the introduction of the Athlon (formerly K7) processor, AMD added 24 additional instructions to 3DNow!. The 3DNow! extensions also gained the support of chipmakers Cyrix and Centaur Technology, now owned by VIA. Notably missing from this loose alliance was Intel, which introduced its own Streaming SIMD Instructions (SSE) in early 1999.

3G: the third-generation cellular telephony standard, which boosted the data-transfer rate to 2Mbps.

3GIO: Third-Generation Input/Output. An internal system bus for PCs developed by Intel, intended to replace PCI. It has been renamed PCI Express. See PCI Express, PCI, HyperTransport, ISA, EISA.

4004: the first single-chip microprocessor available as a distinct commercial product. Intel introduced the 4004 on November 15, 1971, about a year after designing the processor for Busicom, a Japanese calculator company. Some earlier microprocessors were multichip implementations or were sold only in complete systems. Others were secretly developed and used only in military applications, such as the U.S. Navy's F-14 Tomcat jet fighter.

419 scam: financial fraud that originates in Nigeria ("419" is a relevant clause in the Nigerian criminal code). Usually the fraud takes the form of e-mail messages that attempt to convince the recipient to transfer money or reveal bank account numbers in a scheme to obtain larger amounts of money.

45nm: a 45-nanometer semiconductor-fabrication technology that began mass production in 2007. See fabrication.

4G: the fourth-generation cellular telephony standard, also known as LTE (Long-Term Evolution).

4K: a digital display having a horizontal resolution of about 4,000 pixels. ("K" in this case = 1,024.) Although the professional 4K standard is truly 4,096 x 2,160 pixels, the consumer standard is only 3,840 x 2,160 pixels, because "4K" has become synonymous with Ultra High Definition Television (UHDTV), the successor to High Definition Television (HDTV). Consequently, the professional standard for digital cinematography and projection has a 19:10 aspect ratio, whereas the consumer standard has the same 16:9 aspect ratio as HDTV. See HD, UHDTV, pixel, aspect ratio.

5G: the fifth-generation cellular telephony standard, which began deployment in 2019–2020.

65nm: a 65-nanometer semiconductor-fabrication technology that began mass production in 2005. See fabrication.

666.66: suggested retail price of the Apple I personal computer when first sold in April 1976. Not a satanic allusion. The retail price was a 33% markup from the wholesale price of $500, rounded to $666.66 because inventor Steve Wozniak was inspired to use a string of identical numbers by his association with the first dial-a-joke phone service, which adopted a similar phone number to solve the problem of callers dialing the wrong number. (Editor's note: Woz answered this question for me during the 30th anniversary reunion of the Homebrew Computer Club at the Computer History Museum in 2005.)

68000: the first in a family of 16- and 32-bit microprocessors introduced by Motorola in 1979. Major members of the 68K family include the 68020, 68030, 68040, and 68060. In performance and features, those processors roughly compare to Intel's 286, 386, 486, and Pentium, respectively. 68K processors are based on a CISC architecture that's generally cleaner than Intel's x86, though they're not always faster. Computer platforms that have used 68K chips include the original Apple Macintosh, Commodore Amiga, Atari ST, and early Sun workstations. The 68K architecture is largely obsolete today.

8.3 filenames: filenames having no more than eight characters followed by an optional period and extension of no more than three characters. (Example: TEXTFILE.TXT) Almost all early operating systems required 8.3 filenames instead of the longer names allowed today. By convention, the first eight characters described the file's contents, and the extension denoted the file type. Some typical extensions were .TXT for plain-text files, .DOC for formatted word-processing files, .EXE for executable files (programs), and .GIF for GIF-format graphics files. Many three-letter extensions are still used today.

802.11: a group of IEEE radio standards for wireless networking. Also known as Wi-Fi or WiFi (as adopted by the Wi-Fi Alliance). The current standard is 802.11ax, adopted in 2019, which can operate in two unlicensed radio-frequency bands (2.4GHz and 5.0GHz). Older versions are 802.11 (2.4GHz, 1997), 802.11a (5.0GHz, 1999), 802.11b (2.4GHz, 1999), 802.11g (2.4GHz, 2003), 802.11n (2.4GHz and 5.0GHz, 2009), and 802.11ac (5.0GHz, 2013). The next standard will be an enhanced version of 802.11ax that can operate in three radio-frequency bands (2.4GHz, 5.0GHz, and 6.0GHz), which is scheduled for adoption in 2021. In 2020, the Wi-Fi Alliance retroactively rebranded these standards as Wi-Fi 1 (802.11b), Wi-Fi 2 (802.11a, which is out of alphabetical order), Wi-Fi 3 (802.11g), Wi-Fi 4 (802.11n), Wi-Fi 5 (802.11ac, which includes the original Wave 1 from 2013 and enhanced Wave 2 from 2016), Wi-Fi 6 (802.11ax), and Wi-Fi 6E (enhanced 802.11ax). See IEEE, LAN, NAN, WLAN, Wi-Fi.

90nm: a 90-nanometer semiconductor-fabrication technology that began mass production in 2003. See fabrication.

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AAC: Advanced Audio Coding. Apple's proprietary method of compressing digital audio files for use on iPod portable players and personal computers. AAC is a lossy compression codec that sacrifices some audio quality to shrink the file size. It is similar in concept to another popular compression method, MP3. See codec, lossy, MP3, FLAC, HD-AAC.

ABS: acrylonitrile butadiene styrene is a type of plastic filament that feeds a 3D printer.

ADAS: Advanced Driver Assistance System (pronounced A-dass). A system of computers, sensors, and cameras that can partially or fully drive a motor vehicle. At its low levels, an ADAS is capable of adaptive cruise control, automatic emergency braking, lane-departure warnings, and similar semiautonomous functions. At its highest level, the ADAS can drive the vehicle without any human control. High-level systems are still under testing and development.

ADC: (1) analog-to-digital converter; (2) application delivery controller. (1) A device that converts analog signals into digital signals, usually as part of an interface; see DAC. (2) A specialized computer that accelerates cryptography and other security processing, offloading those tasks from a web server.

ADSL: asymmetrical digital subscriber line, a form of DSL that provides more bandwidth in one direction than in the other. See bandwidth, DSL.

AES: Advanced Encryption Standard. An encryption specification approved by the U.S. government in 2001 for both official and commercial use. It replaces the obsolete Data Encryption Standard (DES). Variations are AES-128, AES-192, and AES-256, which describe the key lengths in bits; longer keys are more secure. See Grover's algorithm, Shor's algorithm, RSA.

affinity: associating a particular software process with a particular microprocessor or processor core in a multiprocessing system. In a dual-core system, for example, the operating-system software may be assigned to run on only one of the processors, leaving the other available for user tasks. Affinity may be set manually or automatically. See multicore, SMP.

AGP: Accelerated Graphics Port. It's a point-to-point channel (technically not a bus) that connects the system chipset to the graphics controller, bypassing the PCI bus. This allows faster graphics performance than with PCI-based graphics controllers. The AGP channel is 32 bits wide, like PCI, but runs at higher frequencies and can transfer more data per bus cycle. Bus speeds are 66.6MHz (AGP-1x), 133MHz (AGP-4x), and 266MHz (AGP-8x). Intel introduced AGP in 1996.

AGU: address-generation unit. A function unit in a microprocessor that calculates memory addresses. When a branch instruction redirects the program flow, the AGU calculates the memory address of the instruction that's the target of the branch.

AI: artificial intelligence. (1) The hypothesis that computers can achieve humanlike intelligence, including self-awareness. (2) Any computer program or program routine that simulates intelligence. Definition #2 is widely used, often to describe the behavior of computer-generated characters in games and virtual worlds, but definition #1 is used by scientists. True AI has never been achieved. See Turing test, ML, DL, singularity, GPT.

AIO: all-in-one. (1) A one-piece personal computer with an integrated video monitor; (2) a CPU cooling kit including all required parts; (3) a printer that also functions as a flatbed scanner, photocopier, and fax machine—also known as a multifunction printer (MFP).

air gap: the physical separation that completely isolates a computer from the Internet. When absolute security of a computer or the files it contains is essential, it is disconnected from the Internet and all networks connected to the Internet. Although a wireless-network (Wi-Fi) connection is literally an "air gap," for this purpose it's as forbidden as a wired connection. Air gapping is often used to protect some vital computers operated by the government, government security/defense contractors, businesses that handle very sensitive data, and privacy-minded individuals.

AJAX: Asynchronous JavaScript and XML. Web developers use this term to describe a collection of technologies for dynamically updating web pages in response to user input. They enable developers to build interactive web-based applications. See JavaScript, XML, Web 2.0.

Alpha: a 64-bit RISC microprocessor architecture introduced by DEC (the former Digital Equipment Corp.) in 1992. Compaq inherited the Alpha by acquiring DEC in 1998; Hewlett-Packard inherited the Alpha by acquiring Compaq in 2002. In 2001, Compaq announced it would stop developing Alpha processors after 2003 and Alpha-based systems after 2004.

alpha: a stage of product development preceding the final release. Products at the alpha stage lack some features specified in the design. When the product is feature-complete but still has known bugs, it reaches the beta stage. See beta, release candidate, gold master.

alpha blending: a technique for making 3D objects in computer graphics appear more realistic. It blends multiple textures together, allowing fog effects and the reduced visibility of distant objects.

alpha geek: the most technically proficient person in a group of people.

altcoin: alternative coin, or digital currency. A currency that exists only in digital form and isn't backed by gold, silver, a government, or central bank. The most widely known altcoin is bitcoin. Also known as cryptocurrency or cybercurrency.

ALU: arithmetic/logic unit. A function unit in a microprocessor that carries out integer arithmetic and logic instructions. Arithmetic instructions operate on whole numbers (such as 2+2=4), and logic instructions typically compare values (is X equal to Y?).

Amiga: a largely defunct personal-computer platform originally sold by Commodore. Introduced in 1985, the Amiga 1000 was arguably the first true multimedia computer. It had features that took other platforms years to match, including the ability to display thousands of colors, stereo sound, built-in speech synthesis, a multitasking GUI operating system, video outputs, mixed video/graphics, and the ability to display multiple screen resolutions simultaneously. After Commodore collapsed in 1994, the rights to Amiga technology passed through several companies, but the platform has never been revived. Emulators allow Amiga software to run on today's PCs.

AMX: Advanced Matrix eXtensions. Intel added these new registers and instructions to the x86 processor architecture in 2021 to accelerate the matrix-math operations common in scientific and machine-learning programs. They are up to 8x faster than using AVX-512 instructions for the same tasks. The Golden Cove CPU core was the first to include AMX. The first AMX definition has 12 new instructions and a new register file with eight two-dimensional "tiles," each with 16 entries of 512 bits. Instructions can operate on 8-bit integer or 16-bit floating-point data.

Android: the most popular operating system for cellular phones, tablets, and other mobile devices. First released in 2008, it was created mainly by Google and the Open Handset Alliance. It's based on the Linux kernel but was optimized for mobile devices instead of for desktop computers and servers. Later versions target smart TVs (Android TV), motor vehicles (Android Auto), and wearable devices such as smart watches (Wear OS). It runs on Arm and x86 microprocessors.

anisotropic filtering: a technique that improves the appearance of textures mapped onto 3D objects. Without it, textures may appear unnaturally elongated on curved surfaces. Anisotropic filtering compensates by modifying the textures when projecting them onto the surface.

ANN: artificial neural network. See neural network.

anti-aliasing: a technique that smooths the edges of diagonal lines on the screen and in print. Without anti-aliasing, diagonal lines often have a "jaggy" appearance caused by the stair-step effect of the pixels. Anti-aliasing blurs the edges of the lines. In 3D graphics, bilinear and trilinear filtering provide anti-aliasing for textures.

AOL: America Online. A proprietary computer network and Internet service provider (ISP) founded in the 1980s that became very popular in the 1990s. Its predecessors were PlayNET and Quantum Link (Q-Link); it was renamed America Online in 1989. After several corporate transitions, AOL is much less popular today though still active.

Apache: free, open-source web-server software that runs on Linux and Unix. Apache is an economical, reliable, and popular way to host a website.

API: application programming interface. A collection of subroutines—usually part of an operating system—that application programs can call upon to perform common tasks. For example, a program might call an API routine to display a window on the screen. An API may also allow different programs to work together, such as plug-ins for Adobe Photoshop. APIs reduce the amount of code that programmers must write.

APOP: authenticated POP3. A variation of the POP3 e-mail protocol that requires a POP3 mail client to authenticate itself to a POP3 mail server before receiving e-mail. APOP is a more secure alternative to sending a POP3 username and password in clear text to the server. See POP3.

app: an abbreviation of application that often describes small programs for smartphones and tablets.

Apple II: one of the first three personal computers introduced in 1977 that were sold preassembled, ready to use. In contrast, the Apple I (1976) didn't come with a case or even a power supply as standard equipment. The Apple II was designed primarily by Apple co-founder Steve Wozniak (with some advice from co-founder Steve Jobs) and introduced many improvements over the Apple I, although the basic design was the same. Together with the Commodore PET and TRS-80 Model 1, the Apple II helped move computing beyond the electronics-hobbyist era toward mass popularity. See PET, TRS-80.

applet: (1) a small program; (2) a Java program that runs inside a web browser under security restrictions that limit what the applet can do.

application: a software program that serves some direct purpose for users. A word processor or a game is an application, but an operating system is considered to be system software, not application software. Programs that perform system maintenance functions (such as antivirus checkers or disk defragmenters) are often called utilities.

application processor: the microprocessor in a cellphone that runs user applications, such as the address book, text-messaging program, e-mail program, web browser, etc. The application processor is distinct from the baseband processor, which performs lower-level functions required for wireless communications. Often, both processors are integrated on the same chip.

APT: advanced persistent threats. Malware that strives to hide its presence after infecting a computer or network and automatically reinstall itself if removed. These malicious programs usually mine the infected systems for confidential files and secretly send the data to the perpetrator. Their intent is to quietly steal information, not to disrupt operations. See malware.

AR: augmented reality. A view of the real world enhanced with computer-generated data. This term often describes AR goggles or glasses, which superimpose data on the wearer's view of the real world. For example, looking at a person may allow the glasses to display the person's name, occupation, or other data. Only the wearer can see the data. By contrast, VR (virtual reality) goggles or glasses completely replace the wearer's view of the real world with images of an artificial world. See MR, XR.

architecture: In the context of microprocessors, a family of chips that shares related features and can run the same software. Important features are the instruction set and the register file.

ARG: alternate reality game. A game played in the real world with players connected over the Internet or a cellular network. The game is usually supervised by a person (the "puppet-master") who provides clues and introduces obstacles.

artificial intelligence: (1) The hypothesis that computers can achieve humanlike intelligence, including self-awareness. (2) Any computer program or program routine that simulates intelligence. Definition #2 is widely used, often to describe the behavior of computer-generated characters in games and virtual worlds, but definition #1 is used by scientists. True AI has never been achieved. See Turing test, ML, DL, singularity, GPT.

ASCII: American Standard Code for Information Interchange, a method of representing text (numbers, letters, punctuation, and special characters) as numbers that computers can manipulate. ASCII assigns each character a number; for example, uppercase A is ASCII code 65. Invisible characters—such as tabs, linefeeds, and carriage returns—also have ASCII codes.

ASIC: application-specific integrated circuit. A chip specially designed for a particular application—unlike general-purpose microprocessors, which are designed to be suitable for many different applications.

ASLR: address-space layout randomization. The practice of storing critical program code in a different memory region each time the program loads. The goal is to foil malware that attacks a computer by targeting critical code (usually, the operating system) at specific memory addresses. The latest versions of Windows, Mac OS X, and some versions of GNU/Linux use ASLR.

ASP: active server page. ASPs are dynamic web pages that can change in response to user input or environmental variables (such as the type of computer with which the user is accessing the page). ASPs often display responses to database queries. ASPs require a web server running a Microsoft Windows operating system.

aspect ratio: the relative size of one dimension of a rectangle when compared with the other dimension. A perfect square has a 1:1 aspect ratio, because both dimensions are the same. A rectangle whose horizontal dimension is twice as long as its vertical dimension has a 2:1 aspect ratio. These ratios often describe the shapes of video screens and camera formats.

assembler: a programming tool for writing assembly language.

assembly language: a low-level programming language that substitutes mnemonics (short abbreviations, such as ADC for "add with carry") for the binary codes of machine instructions. Technically, the binary codes of machine instructions are "machine language," but sometimes the terms assembly language and machine language are used interchangeably.

ATA: Advanced Technology Attachment. ATA was an I/O specification for PCs, specifically for hard disk drives. "Advanced Technology" refers to the IBM PC-AT computer introduced in 1984. ATA worked with the parallel IDE/EIDE bus and was updated several times over the years. It has been replaced by serial standards. See IDE, EIDE, Serial ATA.

Athlon: an x86-compatible microprocessor from Advanced Micro Devices (AMD), formerly known as the K7. It was a superscalar, out-of-order processor with speculative execution and branch prediction. Introduced in 1999, the Athlon became the first mass-production x86 processor to reach a clock frequency of 1GHz (1000MHz).

ATM: (1) asynchronous transfer mode; (2) Adobe Type Manager; (3) automatic teller machine. Asynchronous transfer mode is a low-level network protocol that transfers data in 53-byte packets. Adobe Type Manager is a program that allows a computer to use Adobe PostScript-format type fonts. An automatic teller machine is a computer that provides round-the-clock access to personal bank accounts.

ATX: an industry-standard motherboard (main circuit board) for personal computers. Announced by Intel in 1995, ATX motherboards rearrange the motherboard components for greater efficiency and manufacturing economy, and they stack the rear connectors in two rows to save space. Measuring 12 x 9.6 inches, they are typically found in full-size desktop computers. They replaced the earlier AT and Baby AT motherboards. See Micro-ATX, Mini-ITX, BTX, motherboard, mainboard.

AV: (1) audio/video; (2) antivirus.

avatar: an on-screen graphic (usually a face or body) that represents a user in cyberspace. Some graphical chat rooms allow users to choose or design an avatar as their online personas; other users can see and interact with the avatar. See metaverse.

AVX: Advanced Vector eXtensions. Intel added these new instructions and registers to the x86 processor architecture in 2011 beginning with the "Sandy Bridge" chip. The 14 new instructions perform vector-math operations on 256-bit registers that store eight 32-bit floating-point numbers or four 64-bit floating-point numbers. They can also perform 128-bit vector operations. In 2013 with the "Haswell" processor, Intel introduced AVX2 (a/k/a Haswell New Instructions), which added 256-bit vector operations for integers and fused multiply-accumulate (FMA) operations. In 2016 with the "Knights Bridge" processor, Intel introduced AVX-512, which expanded the vector registers to 512 bits. Vector math is common in scientific programs and graphics. See x86, microprocessor, architecture.

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B2B: business to business. Usually it describes a business model in which a vendor sells products or services to other businesses, not to consumers.

babble-rouser: derogatory term for rabble-rousers who babble, especially those who post their ignorant screeds on the Internet. (Coined in 2002 by Tom Halfhill)

back door, backdoor: a secret method by which someone can enter a protected website, computer, or software program. Usually the back door was created by the programmer or engineer who designed the system. Ordinary users are generally unaware of the back door, which may have been created for the purpose of stealing information or planting malware.

backside bus: a special interface that connects a microprocessor to a Level 2 (L2) cache. No other system devices share the backside bus. This contrasts with the frontside bus, or system I/O (input/output) bus, which many system devices typically share. A backside bus helps eliminate performance bottlenecks.

bandwidth: the data-carrying capacity of a communications channel. More is better.

base station, basestation: a local radio transmitter/receiver in a cellular telephone network. Cell phones connect to the global telephone network or Internet through the nearest base station, which is usually mounted on an antenna tower. These large macrocells may be supplemented by smaller base stations known as microcells, metrocells, picocells, and femtocells. Each cell can handle a certain number of cell-phone users (voice or data). A macrocell may handle thousands of simultaneous users; a femtocell may handle fewer than ten users.

baseband processor: the microprocessor in a cellphone or other communications device that performs low-level functions required for wireless communications. Cellphones also have an application processor for running higher-level software, such as the address book, text-messaging program, e-mail program, etc. Often, the baseband and application processors are integrated on the same chip.

BASIC: Beginner's All-purpose Symbolic Instruction Code. BASIC is a programming language invented in the 1960s for teaching purposes. Later, BASIC became a powerful language often used by professionals. Microsoft's Visual Basic is the most popular current version but has little resemblance to traditional BASIC.

BBS: bulletin-board service. A remote computer that usually hosts discussion groups and offers software for downloading, typically over one or more phone lines connected to modems. Hundreds of these automated systems, often operated by individuals, were popular in the 1980s. In the 1990s, they were largely supplanted by Internet newsgroups and then by websites. See modem, World Wide Web.

benchmark: a performance-measurement tool, utility, or application. Benchmark tests can measure the performance of microprocessors, disk drives, graphics cards, network connections, or a whole computer system. Some benchmark tests are sanctioned by industry organizations and others are created by private companies, publications, or individuals. Synthetic benchmarks are programs written expressly to measure performance. Application-level benchmarks are real programs whose performance is carefully monitored. See Dhrystone, EEMBC, and SPEC.

benchmarketing: the use (or misuse) of benchmark scores for product marketing.

BeOS: a now-defunct operating system created and owned by Be Inc., a company founded by some former Apple employees in the 1990s. BeOS originally was released for IBM/Motorola PowerPC processors and was later ported to Intel x86 processors. BeOS had powerful multimedia capabilities.

beta: a stage of product development preceding the final release. Products at the beta stage are supposed to have all the features specified in the design, but they also have known problems ("bugs"). Developers distribute beta versions of the product to testers who look for additional problems. A product may go through several beta cycles of testing and fixing before it's deemed ready for release. See alpha, release candidate, gold master.

BGA: ball grid array. A type of package for chips that uses tiny "balls" instead of pins to make the electrical contacts with the socket.

bi-endian: the ability of a microprocessor to handle multibyte values in either little-endian or big-endian formats.

BIBO: "bias in, bias out." The principle that feeding biased data into a machine-learning system will produce biased results. BIBO is a recent variation of GIGO ("garbage in, garbage out"), a much older computing principle.

big data: slang term for large data sets. A company or government might have large amounts of data to sift for useful information or research. This term derives from big iron, industry slang for a large mainframe computer or supercomputer.

big endian, big-endian: a multibyte value that begins with the most significant byte (MSB), which is stored at the lowest memory address. The opposite is little endian. Microprocessors are often described as big endian or little endian, depending on how they store multibyte values. For example, the IBM/Motorola PowerPC architecture is big endian. Some architectures can handle both formats and are bi-endian.

big iron: slang term for a large mainframe computer or supercomputer. Big iron is for crunching big data, a related term that means large data sets.

binary: the number system used by computers. Binary has only two digits (0 and 1) that are known as bits (BInary digiTs). Electronic circuits represent bits by varying the voltage of electrical signals. Transistors can act as switches with two states—on (binary 1) or off (binary 0). Internally, computers store and manipulate all data in binary.

binary code: the actual program code a computer executes. Programmers write in source code, which a compiler converts into binary code (also called object code, executable code, or machine code). Binary code is specific to a particular microprocessor architecture, so a program compiled for an x86 processor won't run on a PowerPC processor or vice versa.

BIOS: basic input/output system. It's a low-level part of the operating system found in IBM PC-compatible computers. Unlike the rest of the operating system, it's stored in ROM or flash ROM chips on the motherboard instead of on the hard disk. The BIOS is responsible for initializing the computer during startup and performing other low-level functions.

BIST: built-in self-test. Computers and peripherals often have a small program that runs and checks for problems when the power is switched on. The BIST program is usually stored in ROM or flash memory. Also known as POST (power-on self-test).

bit: a binary digit, 0 or 1. Computers process all information digitally in the form of bits. Eight bits make a byte, 1,024 bytes make a kilobyte, 1,024 kilobytes make a megabyte, etc. See byte.

bitcoin: a digital currency independent of any nation or central bank. This software-governed cybercurrency or cryptocurrency exists electronically, not as physical cash. Transactions are recorded but encrypted, so it can be used to avoid financial regulations and sales taxes or to conduct illegal business. Miners or cryptominers create bitcoin by using computers to solve complex mathematical algorithms that become progressively more difficult, so the amount of currency is limited and grows more slowly over time. In practice, bitcoin behaves more like a commodity than a currency. Its value is volatile but trends hyperdeflationary, which discourages spending and especially lending. Because the bitcoin software records all transactions in a distributed digital ledger called a blockchain, it's too slow for general commerce and is massively energy inefficient. Some newer digital currencies address these flaws. See also blockchain, cryptocurrency, cryptomining, CBDC, ewallet, hype coin, idiot coin.

BIX: Byte Information eXchange. A text-only online service that Byte magazine launched in 1985. It was used internally by the magazine staff and also was open to anyone by subscription. It continued in the 1990s until superseded by the Internet-based World Wide Web (WWW). See Byte (magazine).

black box: (1) hardware or software that performs a function without visibility into its operation; (2) any hardware device that performs a needed function.

black-hat hacker: A malicious computer hacker. See hacker.

bleeding edge: descriptive term for a product, technology, or company at the forefront of its field. Derived from "leading edge," it implies that getting too far ahead of the market is hazardous to survival.

blockchain: a shared data file that works like a distributed digital ledger for recording transactions. Most often, blockchains are the ledgers for digital currencies. Example: an encrypted blockchain records all bitcoin transactions and is shared among all bitcoin owners. Each transaction updates the blockchain. Sharing the blockchain ensures redundancy if any copy is destroyed. The alternative is a trusted central repository known as a single source of truth. Although blockchains record all transactions, strong encryption can keep the parties anonymous. For this reason, digital currencies are popular with criminals. Blockchains can be useful for various purposes but tend to be slow and energy inefficient. See bitcoin, cryptocurrency, miner, Ether, Ethereum, Genesis block.

blog, blogging: see weblog.

blogger: one who blogs. See weblog.

blogosphere: the global community of blogs. See blog, weblog.

Blu-ray: an optical-disc format that greatly increases the capacity of DVD-size (4.75-inch) discs. It's named for the blue lasers whose shorter-wavelength light allows more data to be recorded in the same space. (Ordinary DVDs and CDs use red lasers.) Also, Blu-ray records data in multiple layers. Maximum available capacity is 50GB. Can be used to store video or computer data. Blu-ray has enough capacity and speed for high-definition (HD) video. In a format war that essentially ended in 2008, Blu-ray defeated its rival, HD-DVD. See CD, DVD, HD, HD-DVD.

bluejacking: penetrating a Bluetooth-standard wireless network as a prank or for malicious purposes. (Word origin: Bluetooth + hijacking.) Variations: bluejack, bluejacked. See Bluetooth, hacker, Wi-Fi, wardriving.

Bluetooth: an industry standard for wireless communications over relatively short distances. Bluetooth was originally conceived in the 1990s by Ericsson to eliminate the clutter of peripheral cables and to allow portable computing devices to communicate wirelessly with each other and with PCs and networks. Operating in the 2.4GHz range, Bluetooth was originally intended for short-range (10 meters, or 100 meters with amplification), low-bandwidth (723.2Kbps master-to-slave, 57.6Kbps slave-to-master) communications, either point-to-point or point-to-multipoint. Later versions of the standard have significantly improved data rates, up to 24Mb/s with Bluetooth 3.0 + High Speed.

BOFH: bastard operator from hell. A tech-support term for a stupid computer user.

BOM: bill of materials. A product's total component cost, excluding such additional expenses as assembly, shipping, marketing, etc.

Boolean logic: a formal way of defining conditions using operators like AND, OR, and NOT. Internet search engines typically apply Boolean logic to the user's search terms. Programmers use Boolean logic to define conditional statements. Developed by English mathematician George Boole in the 1800s.

boot: to start up a computer. During the boot process, the computer loads the operating system and may also begin running one or more application programs.

boot drive: the disk drive that loads the operating-system software into memory when a computer is switched on. This process is known as "booting the computer."

booth bunny: insensitive term for a pretty young woman hired to attract businessmen to a trade-show exhibit. They rarely know anything about the products on display; they function merely as flypaper, usually in skimpy costumes.

bootloader: a small program that initiates a computer's startup procedure. Typically, the bootloader launches the operating system. See secure boot.

BOPS: billions of operations per second. Often used to express the performance of a DSP or microprocessor.

bot: a computer program that performs an autonomous function. Once started, a bot requires little or no supervision and often runs quietly in the background. Originally, bots were benevolent programs that helped manage online discussion groups and chat rooms. More recently, malevolent bots have become common. They secretly run on an unsuspecting user's computer and perform some mischief, such as sending e-mail spam to other computers on the Internet. Some bots are designed to converse in chat rooms, posing as humans. See botnet, spam, zombie.

botnet: a virtual network of bots working together for a common purpose. Each bot runs on a different computer, sometimes without the knowledge of the computer's owner. Malicious botnets may send e-mail spam to other computers on the Internet or participate in identity theft. In 2007 it was estimated that 11% of PCs are infected with bots and that botnets send more than 80% of spam. See bot, spam, zombie.

brain dump: the act of quickly bringing someone up to speed on a subject by sharing the most important things they need to know. Example: "John is an expert on networking; ask him to give you a brain dump." Derived from core dump.

branch: a program instruction that diverts the flow of execution along two or more alternate paths. For example, a dialog box with "OK" and "Cancel" buttons represents a branch in the program. Depending on which button the user clicks, the program will execute one path of instructions or the other.

branch prediction: the ability of a microprocessor to predict the outcome of conditional branches. The sophistication of this ability varies greatly, from static prediction (always guessing a branch will fork in the same direction) to dynamic prediction (basing predictions on previous behavior).

branch target: the destination of a branch instruction—another instruction at an address in memory.

brick and mortar: describes a business that's not online. Example: " competes with brick-and-mortar bookstores."

bricked: when an electronic device is rendered useless by a hardware or software problem, perhaps forever. Example: "I downloaded a buggy BIOS update, and now my computer is bricked."

broadband: in computer terminology, an Internet connection that runs at about 1Mbps or faster. Cable modems, DSL modems, and T1 lines all provide broadband speeds, although they can vary greatly. In contrast, an older ISDN connection (up to 128Kbps) was considered middleband, and an ordinary analog telephone modem (up to 56Kbps) is narrowband. See cable modem, middleband, modem, narrowband, fraudband.

brogrammer: a male computer programmer. This mashup of "bro" (brother) and "programmer" is a somewhat macho term sometimes resented by female programmers. Related term: brogramming.

BSOD: blue screen of death. The blank blue screen that sometimes appears when a Microsoft Windows operating system crashes. The only recourse is to reboot.

BTX: Balanced Technology eXtended, a new specification for desktop PC motherboards announced by Intel in 2003. BTX offers several improvements over ATX, including three different motherboard sizes and two height specifications. BTX enables the design of smaller, cooler-running PCs but didn't become popular. See ATX, Mini-ATX, Micro-ITX, motherboard, mainboard.

buffer: some memory set aside for a special purpose, usually to allow two devices to exchange data without overwhelming their input/output interfaces. The buffer acts as a temporary reservoir for data. Video cards have very large buffers, often called frame buffers, to store the data for screen displays.

bug: a defect in a computer program or computer-controlled device. Bugs usually cause the program or device to behave in unexpected ways or to stop working altogether. Contrary to popular belief, the term did not originate when a dead moth was found in the wiring of an early computer; it actually pre-dates computers, and engineers were using it by 1878.

bunny suit: slang term for a full-body protective suit worn by workers in a chip-fabrication plant. Unlike most other occupational protective suits, bunny suits protect the products and equipment, not the workers, from contamination; a tiny speck of dust can ruin a silicon wafer or chip. Bunny suits made their debut at Intel's Fab 3 in Livermore, California in 1973 and became standard at all Intel fabs by 1980. They are constantly evolving.

burn rate: the rate at which an unprofitable company (usually a startup) spends its capital. Example: "At our current burn rate, we have enough money for another six months."

bus: a datapath over which two or more components communicate with each other. There are many types of buses. Examples include the PCI bus, which supports the PCI slots in a PC, and the CPU's system bus, which the microprocessor uses to communicate with the rest of the system.

bus bandwidth: the data-carrying capacity of a bus. To calculate maximum theoretical bus throughput, multiply the bus frequency times the bus width. If a 100MHz bus is 64 bits wide, it transfers 8 bytes per clock cycle 100 million times per second, for a maximum theoretical throughput of 800MBps.

buttberry: slang term for a BlackBerry two-way text messaging device. Adopted because BlackBerry devices are often worn as a belt accessory on the hip.

BYOD: bring your own device. A company policy allowing employees to use their personal smartphones, tablets, and other computing devices for work-related tasks and perhaps to connect them to the company's network.

Byte (magazine): the world's second personal-computer magazine, founded in 1975 shortly after Creative Computing. Based in Peterborough, New Hampshire, Byte was founded by Wayne Green, his ex-wife Virginia Londner Green, and Carl Helmers. Two months after the premiere September 1975 issue, the magazine broke away from Wayne Green. Throughout the 1970s and 1980s, Byte was enormously influential and was geared toward serious hobbyists. In 1979, it was sold to the McGraw-Hill publishing company. In 1985, Byte launched BIX (Byte Information eXchange), a text-only online service. In the 1990s, as the industry matured, the magazine reoriented to serve information-technology (IT) professionals as well as enthusiasts. In 1993, Byte began publishing on the new Internet-based World Wide Web (WWW). At its peak, the magazine had about 500,000 paid subscriptions in the U.S. and many more readers with 20 foreign editions. In May 1998, however, McGraw-Hill sold Byte to CMP Media, which surprised everyone by abruptly folding the magazine and laying off the entire staff. The last issue was July 1998. Shortly after this unpopular decision, CMP relaunched Byte in 1999 as a web-only publication with a skeleton staff. It shuttered in 2009. UBM TechWeb acquired the Byte name and relaunched another bare-bones web version in 2011, but it closed in 2013. Neither web version approached the success of the print publication. The Byte magazine online article archive vanished in 2009, but some articles are available using the Internet Archive's Wayback Machine, which preserves a snapshot of the Byte website from 1998.

byte: eight bits. A byte is the basic unit of measure for memory and mass storage. Higher units of measure are expressed as numbers of bytes raised to increasingly large powers of two. A kilobyte is 1,024 (2^10) bytes; a megabyte is 1,024 kilobytes (2^20 bytes); a gigabyte is 1,024 megabytes (2^30 bytes); a terabyte is 1,024 gigabytes (2^40 bytes); a petabyte is 1,024 terabytes (2^50 bytes); an exabyte is 1,024 petabytes (2^60 bytes); a zettabyte is 1,024 exabytes (2^70 bytes); and a yottabyte is 1,024 zettabytes (2^80 bytes). However, disk-drive manufacturers usually round off these values to make them easier to understand, so in that context, a megabyte is 1,000 kilobytes, a gigabyte is 1,000 megabytes, a terabyte is 1,000 gigabytes, etc. See bit, nybble, Byte (magazine).

********** C **********

C#: (pronounced "C sharp") a new high-level, object-oriented programming language introduced by Microsoft in 2001 that combines features of C, C++, and Java. Like Java programs, C# programs can run on a virtual machine, offering the possibility of hardware-platform independence. C# is part of Microsoft's .NET initiative.

C, C++: (pronounced "C" and "C plus plus") two closely related programming languages often used by professionals for software development. C came first and is a conventional procedural-type language. C++ came later and adds object-oriented extensions.

cable modem: a device that allows a personal computer to access the Internet over cable TV lines, which is much faster than an analog telephone modem. The transfer rates of cable modems range from less than 1 megabit per second to more than 10 megabits per second. The digital cable-modem signals don't interfere with cable TV reception.

cache: a block of memory that temporarily holds data for faster access. In the context of microprocessors, caches are usually static RAM (SRAM) chips or cells that operate much faster than dynamic RAM (DRAM) chips.

cache miss: when a microprocessor can't find what it's looking for in a cache. The processor must then look elsewhere in the memory hierarchy: in another cache (if present), main memory, or the hard disk. The penalty in wasted clock cycles increases as the processor moves deeper into this hierarchy.

CAD: computer-aided design. The process of designing something on a computer, rather than on a paper-and-pencil drawing board. Most CAD software runs on powerful workstations, which these days are usually high-end PCs.

candy drop: a malware- or spyware-infected USB flash-memory stick planted in a conspicuous place. When an unsuspecting victim finds the device and inserts it into a computer, it secretly delivers its malicious payload. Candy drops are often planted near their targets—for example, in the parking lot of a company headquarters or government office.

captcha: alphanumeric characters displayed on a web page as a graphic image instead of as plain text. Captchas try to defeat automated computer programs that scan web pages. Sometimes, the captcha may display an e-mail address as a graphic image, in order to defeat programs that harvest addresses for spammers. In other cases, the captcha may display a password that a person must enter to post a comment or access another part of the website; automated programs cannot read the password.

CAS: column address strobe. A signal that together with the RAS locates a memory address in a RAM chip. See RAS, RAM, DRAM, CL1.

Category 5 cable: eight-wire shielded cabling that's commonly used to connect local-area networks. Also known as CAT-5 or CAT5 cable.

catfishing: the crime of adults seducing underage teenagers online. The term derives from catfish, which are bottom-feeders.

CBDC: central-bank digital currency. An official cryptocurrency issued by a nation's central bank as an alternative to private-sector cryptocurrencies such as bitcoin. At present, CBDCs are hypothetical. Given that sovereign currencies already exist almost entirely in digital form, the difference would be subtle. One version proposes that ordinary people could open CBDC retail accounts (electronic wallets, or "ewallets") at the central bank without the intermediary of commercial banks. Another version proposes that the central bank would manage the digital ledger (blockchain) instead of distributing it among numerous private-sector computers. The general goal is to create a stable and regulated cryptocurrency that eases transactions. See cryptocurrency, bitcoin, blockchain, ewallet.

CCD: charge-coupled device. It's a chip that contains an array of solid-state light sensors. Each sensor generates an electrical charge in proportion to the amount of light it detects. Many digital cameras and scanners use CCDs to capture and record an image as pixels. The more sensors, the more pixels, and the higher the image resolution (quality).

CD: Compact Disc. An optical-disc format that stores digital data on 4.75-inch plastic platters coated with a reflective surface. A laser scans the surface of the disc to read the data. Maximum data capacity is 650MB-700MB. See CD-R, CD-ROM, CD-RW.

CD-R: Compact Disc Recordable. A write-once data-storage medium based on CD-ROM technology. A CD-R drive permanently records information on the disc by using a laser to burn microscopic spots on a photosensitive surface. Later, a CD-R or CD-ROM drive can retrieve the information by reading the spots with a laser. CD-Rs cannot be erased or rewritten. Each disc stores 650MB-700MB.

CD-ROM: Compact Disc Read-Only Memory. A data-storage medium for computers based on the same principles used for audio CDs—information is permanently recorded on the disc by etching microscopic pits on a metal surface, and a laser reads the pits to retrieve the information. CD-ROMs cannot be erased or rewritten. Each disc stores 650MB-700MB.

CD-RW: Compact Disc Rewritable. A standard that allows a CD drive to write, erase, and rewrite data on a special disc a virtually unlimited number of times. The drive has a laser that writes and erases data by heating up the disc surface. Early CD-ROM drives cannot recognize CD-RW discs, because their laser pickups aren't sensitive enough to read the less-reflective surfaces. Most CD-ROM drives made after 1997 can read CD-RW discs.

CGI: common gateway interface. A protocol that allows web pages to launch small programs or "scripts" on a web server. Usually a CGI program creates a dynamic web page that returns some information to the user in response to input. Perl is a popular language for writing CGI scripts.

chatbot: a computer program that can mimic human responses in conversation. Early examples, such as Eliza (1966), relied on canned responses and vague language. Today's chatbots, such as ChatGPT, employ machine learning and sophisticated language analysis. See GPT, ML, DL, AI.

ChatGPT: a chatbot based on GPT (Generative Pre-trained Transformer), a computer program that mimics human responses in conversation. See GPT, ML, DL, AI.

chia: a digital currency that competes with bitcoin and many others. Unlike most, however, its creation ("mining") requires allocating mass-storage space instead of solving math problems. Consequently, it inflates the cost of disk drives, whereas other digital currencies inflate the cost of processors. Both methods are wasteful. See bitcoin, cryptocurrency.

chimping: interrupting the act of photographing with a digital camera to look at recently taken pictures on the camera's LCD screen.

chip: an integrated circuit—electronic circuitry shrunk to fit on a single flat piece of silicon. The actual silicon is usually sealed inside a black ceramic or plastic package, which also is generally known as a "chip." This term has additionally broadened in recent years to include devices that combine multiple chips in one package resembling a single chip. Often the term refers to a microprocessor, but there are many other types of chips, such as memory chips and input/output interface chips. See microprocessor, chipset.

chipset, chip set: one or more integrated-circuit chips designed to work together. Recently, this term applies to "chipsets" comprising only one chip, because high-scale integration crams more circuitry onto a single piece of silicon. Usually, a chipset works with a microprocessor. It adds more features, such as input/output interfaces for peripherals and network connections. Chipsets are cheaper than integrating all the features in the processor.

Chrome OS: an operating system introduced by Google in 2009. It's derived from a stripped-down version of the Linux kernel. Tightly integrated with Google's Chrome web browser, Chrome OS is designed mainly for cloud computing, which relies on a continuous Internet connection. It is available on a limited number of devices and isn't intended for general-purpose use on desktop PCs. See Linux, cloud computing, operating system.

CISC: complex instruction-set computing. CISC is an architectural design style for microprocessors that dates to the 1970s. CISC processors try to conserve memory and other system resources by encoding program instructions in a compact format and by using complex instructions that perform multiple operations. Examples of CISC architectures are Intel's x86 and Motorola's 68K.

CL1, CL2, CL3: on memory chips, these specifications mean CAS latency 1, CAS latency 2, etc. They specify the number of bus clock cycles required for the memory to respond to a data request from the CPU. Lower numbers are better (shorter latency). The specification should match the requirements of the computer's motherboard and BIOS. See CAS, RAM, DRAM, BIOS.

class library: a collection of classes (object definitions) that programmers use to build object-oriented programs. Essentially, it's a prewritten code library that saves programmers from reinventing the wheel so they can develop applications more rapidly.

classical computer: a conventional digital computer that represents numbers in binary format (base 2)—either ones or zeroes. Classical computing is so named to distinguish it from a newer technology, quantum computing, which exploits quantum behavior at the atomic level.

CLI: see command-line interface.

click bait, clickbait: a teaser headline or image on a web page that tempts people to click for more information. It's often misleading or false and usually leads to advertising or political propaganda. Clickbait is especially prevalent on social media such as Facebook and on blogging websites. See listicle.

client: a single-user computer attached to a network. Clients are usually desktop PCs but can also include laptop computers and even hand-held devices. Clients can access servers and sometimes other clients over the network.

clock cycle: one moment in the operation of a microprocessor. An oscillator regulates the processor's actions. During each clock tick, electrical signals flow through circuits and turn transistors on or off. The number of ticks per second is the clock frequency, typically expressed in megahertz or gigahertz.

clock frequency: the operating speed of a microprocessor, interface, or bus in clock cycles per second. It's regulated by a "clock" or oscillator that synchronizes operations. During each clock cycle, transistors switch on and off to redirect electrical current through a chip's circuits. Synonymous with clock speed, it's usually expressed in megahertz or gigahertz. Clock frequency alone does not equal processor performance; processor performance is defined as instructions per clock x frequency.

clock speed: see clock frequency.

clone: a copycat product that tries to be compatible with the original product. The vast majority of today's PCs are cloned descendants of the original IBM PC of 1981. Clones are usually the result of reverse engineering.

cloud: the Internet or any computer network.

cloud computing: using computer resources located elsewhere on a network. Uses may include remote mass storage or the remote execution of software, without downloading or installing the software on the client computer. Recently, cloud computing has become more associated with the Internet than with local-area networks. A similar term, less used today, is server/client computing.

CMOS: complementary metal oxide semiconductor, the most common type of integrated circuit for modern microprocessors and memory chips.

CMP: chip multiprocessing. The integration of two or more processor cores on a single chip. It allows multiprocessing in a single-processor system. Not to be confused with SMP (symmetric multiprocessing), which requires two or more separate processors.

CNN: convolutional neural network. See neural network.

CO: central office—a local telephone exchange.

COA: certificate of authenticity. A label that certifies a copy of software is legitimate—not pirated or counterfeited.

COBOL: COmmon Business-Oriented Language. COBOL is a programming language that dates to the 1950s and was the standard for many years on mainframe computers. Some say that most of the business code still running on computers today was written in COBOL, but it has been largely superseded by modern languages.

code: slang for source code—the instructions that programmers use to write software. In a broader sense, it also describes the executable (runnable) form of a program.

code coolie: derogatory term for a programmer who is assigned to a less-important or boring part of a project.

code expansion: software bloat. Some techniques that boost the performance of microprocessors also result in larger programs. For example, programs for RISC processors are often larger than equivalent programs for CISC processors because the RISC instructions have a greater average length.

code pun: a sequence of program code that can perform multiple tasks, depending on the entry point. Usually it works by jumping the starting point of execution into the middle of an existing routine. Sometimes it jumps into data that can be interpreted as program instructions. A malicious version of this technique is called a gadget or return-oriented programming.

codec: compressor/decompressor. A program that compresses digital data (usually audio or video) to reduce the file size. Lossless codecs preserve the original quality; lossy codecs sacrifice some quality to achieve greater compression. Examples of popular audio codecs are MP3, AAC, and FLAC.

coder: a computer programmer. This term wasn't commonly used before the 2000s. See code.

Colossus: the world's first electronic digital computer. Colossus was a top-secret codebreaking machine built by the British at Bletchley Park, England, to crack German ciphers during World War II. It entered service in January 1944 and was quickly succeeded by Colossus Mark 2, an improved model, in June 1944. The Mark 2 had 1,500 vacuum tubes and remained in operation until 1960. See ENIAC.

command-line interface: a text-based user interface that allows users to control a computer program by typing commands at a screen prompt. Examples: MS-DOS and Linux. See user interface, GUI, DOS.

CompactFlash (or Compact Flash): a standard format for flash-memory cards often used in digital cameras, digital audio players, and other electronic devices. Introduced in 1994, it has been largely replaced by SD-format cards, but some devices use the newer XQD cards, introduced in 2012. See flash memory, SD, XQD, SmartMedia.

compiler: a tool that programmers use to convert their source code into object code (also known as binary code, executable code, or machine code). Object code is the actual code that runs on a computer. Compilers also check for errors in source code.

concurrency: running multiple programs or threads of execution on a computer at the same time. Each program or thread is said to be concurrent. See multiprocessing, multithreading.

conditional branch: a program instruction that forks in two directions, depending on the outcome of a condition. For example, if you click an "OK" button, the program branches in one direction (perhaps saving a file), while if you click a "Cancel" button, it branches in another direction (canceling the operation).

context switch: the result of an interrupt that forces a microprocessor to stop executing the current instruction stream and begin executing a different instruction stream. Generally a context switch happens in response to input from a peripheral, an error, or when a user switches among multitasking programs. During a context switch, the OS must save the contents of the CPU's registers before switching to the next instruction stream, then restore the registers when execution resumes with the original instruction stream.

cookie: a small text file managed by a web browser on the client's local hard disk. It contains information saved by some web servers. Among other things, cookies allow websites to recognize returning visitors and present customized web pages. Despite much hysteria, cookies are rarely dangerous or invasive.

coordinate matrix: A set of numbers required to draw a 3D object on the screen. Each object consists of numerous polygons, often triangles. Each vertex (corner) of each polygon needs a coordinate matrix to describe its location in virtual space. The coordinate matrix is usually a set of four numbers describing the horizontal, vertical, and depth positions of the vertex.

coprocessor: a microprocessor chip that assists the main microprocessor in a computer, usually by handling some specialized task such as graphics.

core: (1) a logic component for chip integration; (2) the main logic circuits of a microprocessor chip; (3) an obsolete type of computer memory consisting of a fabric of tiny wires and doughnut-shaped metal rings. Term 1 usually refers to hard macros or synthesizable intellectual property. Term 2 usually refers to the microarchitecture (internal design) of a processor, exclusive of buses and caches. Term 3 is rarely used these days.

core dump: a screen display or printout of the contents of a computer's main memory or a region of memory. Programmers sometimes use a core dump to help them debug a program. See core (definition #3).

core-logic chipset: two or more chips on the motherboard of a PC that connect the microprocessor to other system devices. The core logic defines many of the features of a PC: how much main memory (RAM) it can use, how many expansion slots it has, the types of system interfaces available, how much memory it can cache, and so forth. Core logic is usually partitioned into two sections known as the north bridge and south bridge. Core logic is also known as the system chipset. See north bridge, south bridge, motherboard.

corner case: in software testing, an action expected to happen rarely. Good testers look for these cases because they often make the program react in ways the designers didn't anticipate, which may cause an error or even crash the program.

CPI: cycles per instruction. A measure of efficiency for microprocessors; the fewer CPI, the better.

CPU: central processing unit. Another term for a microprocessor chip. Sometimes incorrectly used to refer to the main box of a PC.

cracker: a malicious hacker who attacks computers and networks.

craplet: a program of dubious value. Craplets are often preinstalled on new PCs or included on CD-ROMs with other products. See shovelware.

crash: an undesirable event in which a computer program unexpectedly stops running because of a bug or some other problem. If the program that stops running is the operating system, the whole computer may be disabled until rebooted.

crowdfunding: raising money by appealing to donors via the Internet. Usually the goal is to fund a small-business startup that would be difficult to fund conventionally by raising venture capital or obtaining a bank loan.

crowdsourcing: outsourcing labor to users or customers. It saves the expense of hiring staff or contractors, and it gives the laborers a sense of belonging to the project, even if they don't benefit financially. Prime example: the online encyclopedia Wikipedia.

crypto: cryptography, the science of codes and ciphers. See AES, DES, MAC.

cryptocurrency: money that exists only in digital form and isn't backed by a hard commodity, government, or central bank. Synonymous with cybercurrency. So-called miners or cryptominers create it by using computers to solve difficult mathematical problems that verify, record, and encrypt the transactions. Owners can exchange the money digitally to make purchases and repay debts. Transactions are recorded in a permanent, distributed digital ledger called a blockchain. Although the blockchain can verify transactions, the parties can remain anonymous. These qualities make digital currencies attractive to criminals, although they also have legitimate uses. Despite the mathematical limits on the total money supply of any particular digital currency, they have been called the ultimate fiat currencies because any number of them can be created. Indeed, the number of digital currencies already exceeds the number of sovereign currencies. See blockchain, bitcoin, Ether, Ethereum, ICO, CBDC, hype coin, idiot coin.

cryptojacking: (1) secretly hijacking a computer to mine cryptocurrency; (2) secretly encrypting data on a victim's computer and then demanding a ransom to unlock it. The first definition seems to be gaining popularity as malicious websites and malware infect vulnerable computers to secretly generate digital money. The second definition refers to the secret intrusion of ransomware into the victim's computer or network. To avoid detection, the attacker usually operates remotely over the Internet and demands payment in a cryptocurrency such as bitcoin. Victims have included hospitals, police departments, and local governments as well as individuals. The ploy assumes the victim lacks an offline backup of the encrypted data.

cryptomining: the automated process of earning cryptocurrency (digital money) by using a computer to solve difficult mathematical problems that verify and record the currency transactions. Someone who owns or operates the computer is a miner or cryptominer. See also blockchain, bitcoin, Ether, Ethereum, ICO.

CSI: Common System Interface. A high-speed point-to-point serial connection between multiple processor cores and between a processor core and a memory controller. Intel developed CSI to compete with a similar interconnect, HyperTransport. CSI is now known as the QuickPath Interconnect.

CSS: Content Scrambling System, an encryption method for protecting the content on commercial DVDs. See DeCSS, crypto.

cube farm: a large work area with open cubicles instead of private offices. Silicon Valley companies are famous for their cube farms.

cyberchondriac: a person who self-diagnoses a phantom illness after reading about symptoms on the Internet. Amalgam of cyberspace and "hypochondriac."

cybercurrency: see cryptocurrency.

cyberflashing: indecent exposure via email, texting, or social media. A form of sexual harassment, the most common examples are photos of genitals or sexual acts sent from men to unwilling women.

cyberjacking: using a computer to mine a cybercurrency (digital money) without the owner's permission. Sometimes the cyberjacker secretly plants a computer program on a server for this purpose; sometimes the program secretly downloads onto a visiting client computer via the web browser. In any case, the cyberjacking may significantly slow the computer on which it's running. See cybercurrency, cryptocurrency, miner, cryptominer.

cyberpunk: a subgenre of science fiction typified by gritty atmosphere and often a dystopian future. The seminal cyberpunk novel was William Gibson's Neuromancer (1984); a cyberpunk cult film was Blade Runner (1982). See steampunk.

cyberspace: the virtual world of the Internet and the World Wide Web. Cyberspace exists only online, not in physical space. The real world is meatspace.

cybersquatter: someone who reserves a second-level Internet domain (such as "") likely to be desired by another person or especially a company, then offers to sell the domain at a large profit. The practice, known as cybersquatting, was most common in the early days of the World Wide Web. See typo squatting.

********** D **********

D-cache: see data cache.

DAC: digital-to-analog converter. A device that converts digital signals into analog signals, usually as part of an interface. See ADC.

daemon: a program that runs in the background—that is, invisibly or nearly so—usually to provide a service, not a user application. An example of a daemon might be an antivirus checker or a printer-ink monitor. Daemons often load and run at startup and continue running until shutdown unless manually disabled. In Microsoft Windows, press Ctrl-Alt-Del and click on the "Processes" tab to see a list of memory-resident daemons.

dark fiber: fiber-optic cable installed but not in use. Usually this happens when a utility company digs a trench or tunnel and lays extra cable for future capacity; sometimes it happens when the utility goes out of business.

dark silicon: logic circuitry on a silicon chip that is powered down when not in use. Usually this circuitry is intended for a specific purpose (such as video playback) and isn't needed most of the time, so the chip designers isolate it within a separate power domain that can be shut off while the rest of the chip continues to operate.

darknet: a region of the Internet accessible only with special software that tries to keep the users anonymous. Darknets are often used to hide illegal transactions, such as sales of drugs, guns, and malware. See TOR, malware, cryptocurrency.

data cache: a block of fast memory on a microprocessor chip that temporarily holds data for a running program. The processor fetches data into the cache from main memory so it's immediately available when the program needs it. This saves time because data-cache memory (SRAM) responds much faster than main memory (DRAM). The program can also save data (the results of program instructions) into the data cache, where the data is available for subsequent processing. At some point, the processor "flushes" the cache by saving the data back to main memory.

data compression: any method that stores data in less space than the original data requires. There are many forms of data compression. For some applications (such as graphics and sound), lossy compression is tolerable—there is some loss of quality, usually not perceptible or important. For other applications (such as text and numbers), only lossless compression is acceptable—there can be no distortion of the original data.

data mining: sifting through raw data to find useful information. Special programs can automate the process.

data parallelism: performing a large task by reducing it to smaller chunks of data that a computer can process simultaneously. Data parallelism can yield huge gains in performance. However, it usually requires special programming, and not all tasks can be reduced in this manner. See program, instruction parallelism, massively parallel.

data sabbath: one day a week in which a person doesn't use a computer, PDA, or Internet-enabled cellphone. Some people extend their fasting to include all electronic devices.

database: a structured collection of information. See database engine, query engine.

database engine: a program that manages a database, allowing the storage and retrieval of information. The engine may be part of a larger program. See database, query engine, SQL.

datapath: an electrical pathway (a wire) that carries signals representing data. Datapaths connect the transistors inside chips and eventually lead to the contacts that carry signals on and off the chip.

datastream: the flow of data over a wire. See datapath.

daughtercard: a circuit board that plugs into a larger circuit board, usually to provide additional functions.

DAW: digital audio workstation. Computer software for creating, recording, editing, and mixing digital audio. The DAW may include a special control console that's easier to use than a standard computer keyboard and mouse. The most popular DAW in recording studios is Avid's Pro Tools.

DDoS: distributed denial-of-service attack. A DoS attack launched on a target computer from multiple computers on a network. See DoS, packet storm, cracker, hacker, zombie.

DDR-SDRAM: double-data-rate synchronous dynamic random-access memory. A type of memory chip that transfers data twice as fast as regular SDRAM. "Double data rate" means that two bits of data move on or off the chip on each wire during each bus cycle (by synchronizing with the leading and trailing edges of the clock signal).

deadlock: a software bug that stalls two or more multitasking programs (or two or more threads running within a multithreaded program). A condition arises in which a program or thread must wait for another program or thread to finish a task, but the first program or thread is likewise waiting; neither can proceed. The computer appears to freeze. Also called a threadlock.

Debian: a popular version of the GNU/Linux operating system for computers. It was created in 1993 by Ian Murdock (1973–2015), who combined his name with that of his girlfriend Debby to make "Debian." It includes a graphical desktop and all of the system software and application software to make a complete ready-to-use system, also known as a "distribution" or distro. Debian has spawned several derivative versions ("forks"), such as Ubuntu and Mint. See Linux, GNU, kernel, Unix.

debugger: a software tool that helps programmers find and fix the bugs in their programs. Modern development tools have built-in debuggers.

decoder: circuitry inside a microprocessor that figures out what a program instruction is supposed to do. For example, when the decoder finds a multiply instruction, it tells the appropriate function unit to multiply the numbers referenced by the instruction.

DeCSS: a simple computer program released in 1999 that defeats the copy protection on commercial DVDs encrypted with the Content Scrambling System. See CSS, crypto.

deep learning: a technique that trains a computer program to better perform an assigned task. It typically uses a neural network—a program that mimics the function of a human brain.

deepfake: a fake video so realistic it's hard to distinguish from a genuine video. This term also describes the technique employed to make the video, which uses deep learning or generative adversarial networks (GANs). Deepfakes usually alter a genuine video to make it appear a person is saying something that wasn't actually said. Some deepfakes are good-natured spoofs; others put false words into the mouths of politicians or celebrities for propaganda purposes. See shallowfake.

DES: Data Encryption Standard. A cryptography standard developed by the U.S. government in the 1970s. DES was widely used for protecting government and commercial data transmissions until it was cracked in 1998. Its replacements are Triple-DES (3DES) and the Advanced Encryption Standard (AES) approved in 2001.

determinism, deterministic: the ability of a computer system to respond to input or interrupts in a timely, predictable, and repeatable fashion. Example: an anti-lock braking system must respond to the driver's actions on the brake pedal consistently and without delay. In contrast, clicking on a web-page hyperlink usually evokes a nondeterministic response.

development tool: a program that programmers use to write programs. Dev tools come in many forms, but often include a text editor (for entering source code), a compiler (for converting source code into object code), and a debugger (for finding and fixing bugs). See program, source code, object code, compiler, debugger.

Dhrystone: a synthetic benchmark program for measuring CPU performance. Although widely used and quoted, Dhrystone is not an adequate way to evaluate modern CPUs. Even the latest version (2.1) is such a small program that it fits entirely inside the caches of today's processors, thus eliminating the latency of memory I/O. Dhrystone results are expressed in MIPS (millions of instructions per second), but this doesn't necessarily correspond to native MIPS. Dhrystone MIPS are based on the performance of a VAX 11/780, a popular minicomputer introduced by DEC in 1978. The VAX 11/780 could execute 1 MIPS. With the Dhrystone test, 1,757 iterations are equal to one VAX MIPS.

dial-up connection: A connection to a remote network (such as the Internet) through an analog modem over an ordinary telephone line. It's a slower and less convenient connection than a direct digital hookup, such as an ISDN, DSL, or cable modem.

digicam: digital camera. It's a still camera, not a video camera or camcorder, although some digicams can record motion video and some camcorders can record still photos.

DIMM: dual inline memory module. A small circuit board with memory chips (RAM) that plugs into a socket on a motherboard. DIMMs are commonly used to install main memory in a PC. The memory interface is 64 bits wide. Earlier memory boards called SIMMs (single inline memory modules) were only 32 bits wide, so they had to be installed in pairs in PCs with 64-bit memory interfaces. See DRAM, NVDIMM.

DIP switch: a tiny switch that manually controls some function of a computer device. (DIP stands for dual inline package.) DIP switches are commonly found on disk drives, printers, and motherboards.

Direct RDRAM: see DRDRAM or RDRAM.

dirty: programming slang for a data file that has been modified in memory but not yet saved to nonvolatile storage.

disassembler: a software tool used by programmers to convert the executable object code of a program into assembly-language source code. This makes it easier to understand the function of the program when the original source code is not available. See object code, source code, assembler, assembly language.

disruptive technology: the latest buzzword for "revolutionary," which has become so trite and difficult to defend that almost nobody dares to use it anymore. Supposedly, a new technology is disruptive when it obsoletes everything else and rewrites the rules. Actual disruptive technologies are rare. See paradigm shift.

distributed computing: the technique of running a program on many computers simultaneously. Usually the programs operate on data too large to be usefully manipulated by one computer. The distributed computers typically send their results over a local network or the Internet to a remote server for consolidation. See folding@home, SETI@home.

distro: slang for "distribution." Usually it refers to a version of the GNU/Linux operating system that includes all the necessary system software and application software to make a complete ready-to-use system. Examples of popular Linux distros are Debian, Ubuntu, Mint, Red Hat Enterprise, SUSE, Slackware, Arch, Fedora, Chromium OS, and Chrome OS. See Linux, GNU, kernel, Unix.

dithering: combining multiple colors to approximate an intermediate color that a system cannot reproduce exactly. Some computers, graphics cards, or programs have more limited color capabilities than others, so dithering allows them to display images with unavailable colors, albeit with compromises. Dithered colors often look different or grainy.

DIY: do it yourself. Usually refers to a hobby project to build something instead of buying an off-the-shelf product.

DL: deep learning, a technique that trains a computer program to simulate artificial intelligence. Feeding data into the program reconfigures a software structure called a neural network. After training, it can respond to commands and questions in ways that seem humanlike. See AI, ML, GPT.

DLL: dynamic-link library, a program file that loads into memory on demand by another program. Programmers often divide large programs into a main program plus several DLLs to conserve memory when certain features supported by the DLL aren't needed. DLLs also allow programmers to add features or fix bugs without recompiling the main program. Sometimes DLLs conflict with each other in memory or don't respond in the way the main program expected, which can cause a crash.

DLP: digital light processing is a technology employed by some 3D printers that build objects using resin instead of plastic filaments as the raw material.

DNN: deconvolutional neural network or deep neural network. See neural network.

DNS: domain-name server. It's a computer that translates uniform resource locators (URLs) into Internet Protocol (IP) addresses. Every Internet-connected device has a unique IP address; URLs were invented because addresses are hard to remember. For example, when you type the URL into a web browser's address bar, a DNS server on the network converts it to IP address

domain: a region or range of addresses on a computer network. On the Internet, top-level domains include .com (commercial), .net (network), .org (organization), .mil (military), and .edu (educational institution). Second-level domains encompass a smaller range of addresses:,,,,, etc. A third-level domain is even more specific: Inside these domains, local-area networks are divided into even smaller domains at the department level.

dongle: a small device that plugs into a computer I/O port. The most common purpose is for security—the dongle allows a commercial software application to run. When you launch the application, it queries a chip in the dongle and quickly aborts if it doesn't receive the correct response.

doom-scrolling, doomscrolling: obsessively reading endless feeds of world news that's usually bad. The term was coined in 2020 when the news was indeed usually bad: the worst pandemic since 1918, the worst recession since the 1930s, the worst racial unrest since the 1960s, and the worst U.S. president ever.

DOS: (pronounced "doss") disk operating system. A low-level program that allows a computer to interact with mass-storage devices and (typically) other system devices. Although DOS is a generic term, in common usage it refers to MS-DOS (Microsoft DOS), the DOS found on IBM-compatible PCs.

DoS: denial of service. An attack that overwhelms a computer or network with requests for a service, usually for the purpose of disabling the target. For example, a malicious hacker might program a computer to repeatedly access the home page of a website in order to block the requests of other people who want to access the site. See DDoS, packet storm.

dot com, dot-com: a business whose primary or sole presence is online.

dot commie, dot-commie: derogatory term for an employee of a dot-com company.

dot pitch: the distance between the tiny dots that form images on video screens. The smaller the dot pitch, the sharper the picture, although dot pitch isn't the only factor in image sharpness.

double-precision floating point: A floating-point number represented in a computer by 64 bits. Commonly used in financial, scientific, and technical applications. See extended-precision floating point, single-precision floating point.

downtime: the amount of time a computer is shut down for repair or maintenance. It's often used as an inverse measure of availability or reliability for servers—the less downtime, the better. See uptime, five nines.

dox, doxxing, doxxed: to maliciously post someone's personal information or documents on the public Internet. The usual motives are revenge for a perceived offense or to expose the victim to identity theft. See trolling, swatting.

dpi: (1) dots per inch; (2) deep-packet inspection. (1) The number of tiny dots or pixels per inch that a printer or video monitor produces. Higher dpi usually yields a higher-quality image. (2) In networking, the analysis of a data packet's payload, usually to optimize packet forwarding or to scan for malware.

DRAM: dynamic random-access memory. DRAM is RAM that requires a periodic refresh signal to maintain data; SRAM (static RAM) does not. DRAM is also volatile; it loses all data when the power shuts off.

DRDRAM: Direct Rambus dynamic random-access memory. Also known as RDRAM, it's a proprietary memory standard controlled by Rambus that transfers data more quickly than ordinary DRAM.

drive-by attack: malicious software that can infect a computer when a user merely visits an infected website, even without explicitly downloading any files. See malware, hacker, virus, Trojan horse, worm.

DRM: digital rights management. Any method for protecting copyrighted digital content against unauthorized use.

DSP: digital signal processor. A type of microprocessor chip that's optimized for performing repetitive operations on large data sets, especially data converted from analog signals. DSPs are often used for communications, networking, multimedia, and other specialized tasks.

DSL: digital subscriber line, a special service that allows a personal computer to access the Internet over ordinary phone lines at much higher speeds than regular analog modems. DSL modems transmit and receive broadband digital signals over phone lines without interfering with voice communications. Rates vary widely, but usually range from 0.6 to 8 megabits per second. See ADSL.

DSLAM: digital subscriber loop access multiplexer. A bank of DSL modems and related equipment at a telephone company's central office that provides DSL service to customers.

DTD: document type definition. A file associated with an XML document that defines the format of the document's tags. XML is an extensible metalanguage that allows anyone to define new tags, so a DTD declares how those tags should work. An XML document can refer to a public DTD at any URL on the Internet.

dumpster diving: the practice of sifting through trash to find useful information. Malicious hackers can often discover passwords, account numbers, and other vital data by looking at the unshredded trash left in wastebaskets, recycling bins, and dumpsters. See social engineering.

dusty deck: an old computer program that remains useful despite inconveniences; modernizing is considered too much work. The term originates from decks of punchcards that stored programs for old mainframe computers. Usually uncomplimentary. See legacy code.

DVD: Digital Versatile Disc. An optical-disc standard for mass storage that supersedes CD-ROMs. By using multiple layers and both sides of a disc, DVDs can store 4.7GB to 17GB of data, while CDs are limited to a maximum 700MB.

Dvorak: a more efficient but less popular keyboard layout. Patented in 1936 by August Dvorak and William Dealey, it requires less finger motion than the standard QWERTY layout. Although QWERTY is an anachronistic legacy of mechanical typewriters, it remains popular because it's more widely taught. Dvorak keyboards are available for computers, and software can remap QWERTY keyboards for Dvorak.

********** E **********

e-tailer: electronic retailer. An online merchant.

E2EE: end-to-end encryption. Communication from the source to the destination is fully protected by encryption to foil eavesdroppers.

easter egg: a hidden software feature, usually frivolous. Easter eggs are typically invoked by pressing an undocumented key combination or by performing an uncommon sequence of actions. The hidden "feature" may be as simple as the programmer's name or as complex as an animated cartoon. Programmers often sneak easter eggs into the software without management's permission. The first easter egg is generally attributed to Warren Robinette, an Atari programmer in the 1970s who hid his name in an Adventure game to protest a corporate policy against crediting game developers.

ECC: (1) error-correction codes; (2) elliptic-curve cryptography. (1) is a method of verifying that a data transfer has not been corrupted by a transitory error; it is often used in computer memory interfaces. (2) is a public-key cryptography algorithm.

EDA: electronic design automation. Software tools used by engineers to design and test electronic circuits for chips.

eDRAM: embedded dynamic random-access memory. A type of DRAM integrated on logic chips, such as microprocessors. This requires special manufacturing techniques. Normally, the type of memory integrated on logic chips is SRAM. eDRAM is slower than SRAM but cheaper, because it needs only one transistor per memory cell instead of six transistors.

EEMBC: EDN Embedded Microprocessor Benchmark Consortium. An independent industry organization that defines, certifies, and publishes benchmarks for embedded processors. Benchmarks are certified by ECL (EEMBC Certification Laboratory).

EIDE: Enhanced Integrated Device Electronics, an industry-standard I/O interface for connecting disk drives to PCs. EIDE is a parallel-type interface that uses 40- or 80-wire ribbon cables. An EIDE interface can handle two devices, known as the master and the slave. Most PCs have two EIDE interfaces, known as the primary EIDE and secondary EIDE. This permits a total of four EIDE devices. The Ultra ATA-66, ATA-100, and ATA-133 standards require an 80-pin EIDE interface. EIDE is commonly called "IDE," which is actually an older version of the standard. It is being superseded by Serial ATA.

EISA: Extended Industry Standard Architecture, an improved 16-bit version of the ISA bus found in early IBM-compatible PCs. It's an internal system bus for adding expansion cards and other devices. EISA has been supplanted by PCI. See ISA, PCI, AGP, HyperTransport, 3GIO.

Elaine Herzberg: see Herzberg-Wood, Elaine Marie.

electromigration: the atomic erosion that occurs over time in an active electrical conductor. Electricity passing through a wire can actually wear down the physical structure of the wire, eventually breaking the circuit. Electromigration is becoming a larger problem as microprocessors use thinner wire traces at smaller process geometries.

electronic leash: derogatory term for a mobile phone or wireless pager provided by an employer, especially if the employer uses the device to contact the hapless worker at odd hours.

elegant: good design. Among geeks, to say that some hardware or software is "elegant" is to pay a high compliment. Antonym: kludge.

embarrassingly parallel: a task divisible into an almost endless number of smaller tasks that a computer can execute in parallel. Such tasks can be vastly accelerated by parallel processing. Some tasks cannot be distributed in this way because they depend on the result of another task, so they must execute serially.

embedded processor: a microprocessor or microcontroller inside a non-PC device, such as an appliance, an industrial machine, or a vehicle.

embedded software: a computer program that runs inside a non-PC device, such as an appliance, an industrial machine, or a vehicle. Usually the device stores the program in a ROM or flash ROM chip.

emoji: a small pictorial icon expressing emotion, usually as part of a social-media post or e-mail message. The first emojis are attributed to Shigetaki Kurita, who created them in 1999 while working for a Japanese mobile-phone company. "Emoji" derives from the Japanese words for picture ("e") and character ("moji"). Not to be confused with an emoticon, which also expresses emotion but combines keyboard punctuation marks to create a character-based image.

emoticon: an amalgam of "emotion" and "icon," it's a combination of keyboard punctuation marks that express emotion, usually as part of a social-media post or e-mail message. Some common emoticons are :-) smile :-( frown ;-) wink and :-0 surprise. Not to be confused with an emoji, which also expresses emotion but is a small pictorial icon. Although some historical sources trace emoticons to a typesetting error in an 1862 transcription of a speech by U.S. President Abraham Lincoln, their modern origin dates to 1982, when Scott E. Fahlman suggested their use on computer message boards.

emulator: hardware or software that allows a computer to use programs designed to run on a different, incompatible computer. Emulators work by converting one type of program instructions into another while the program is running, or by translating operating-system calls so they can execute on the native operating system. There is always some loss of performance with emulation, due to the translation overhead, but an emulator may actually exceed the performance of the original computer when running on a much faster computer. See retrocomputing, Three Laws of Emulation.

ENIAC: Electronic Numerical Integrator and Computer, the first electronic digital computer built in the U.S. ENIAC entered service in 1946 and was originally designed to calculate ballistic trajectories for artillery. The machine contained more than 19,000 vacuum tubes and weighed 30 tons. It was shut down for the last time in 1955. See Colossus.

EOL: (1) end of life; (2) end of line. The first usage typically describes a product that its maker has discontinued or no longer supports. The second usage describes one or two ASCII characters that mark the end of a line of text. Usually, pressing the Enter key on a computer keyboard invisibly inserts the EOL character(s), which may be a carriage return, a linefeed, or both. See ASCII.

Epstein's amendment: a modification to Moore's law proposed by Dave Epstein in the 1990s, when he sat on the Microprocessor Report editorial board. The amendment: "Starting in 1970 with the predicted doubling every 12 months, the interval will increase by six months every ten years." In other words, assume that in 1970, Moore's law was still chugging along at a rate of 2x every 12 months. By 1980, it slowed to 2x every 18 months. By 1990, it was 2x every 24 months; by 2000, 2x every 30 months. Epstein's amendment adds a leveling factor that accounts for the law of diminishing returns. See Moore's law, Moron's law.

Ether: a type of currency that exists only in digital form. It's based on the Ethereum open-source cryptocurrency platform. See Ethereum, cryptocurrency, bitcoin, blockchain, miner.

Ethereum: an open-source software platform that enables programmers to create and manage a cryptocurrency. The most common example of a currency based on this platform is Ether. See Ether, cryptocurrency, bitcoin, blockchain, miner.

Ethernet: a networking standard commonly used for local-area networks (LANs). It defines how data travels over the network between computers, network printers, and other devices. Regular Ethernet can transfer data at a maximum speed of 10Mbps; Fast Ethernet operates at 100Mbps; Gigabit Ethernet operates at 1Gbps. See network, LAN, NIC.

EULA: end-user license agreement, the legal contract you must agree to before using new software for the first time. Contrary to popular belief, you don't actually own the software you buy; the publisher licenses it to you. If you don't agree with or obey the terms of the license, the publisher can revoke it. EULAs are controversial and widely ignored.

ewallet: electronic wallet. A cash account for spending money via digital transactions. The account may contain official currency such as U.S. dollars or unofficial currency such as bitcoin. It may be associated with a conventional commercial bank account or with an alternative service such as PayPal. See cryptocurrency, bitcoin, blockchain.

exabit: 1,024 petabits, or 2^60 bits. Abbreviated eB. See bit, byte.

exabyte: 1,024 petabytes, or 2^60 bytes. Abbreviated E, EB, or eB. See bit, byte.

execution unit: a collection of circuits in a microprocessor that executes program instructions. There are different types of execution units for different types of instructions (integer, floating point, multimedia, etc.). Also called a function unit.

ExpressCard: the next-generation PCMCIA standard introduced in 2003. Plug-in cards come in two sizes: 34mm x 75mm and 54mm x 75mm. The I/O interface can support PCI Express and USB 2.0. See PCMCIA, PC Card, PCI Express, USB.

extended-precision floating point: A floating-point number represented in a computer by 80 bits. Available only with x86 processors and rarely used. See double-precision floating point, single-precision floating point.

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fab: a chip fabrication plant. It's the place where the people in dust-proof "bunny suits" work. Building and equipping a modern fab can cost $1 billion to $3 billion. See fabless, fabrication, wafer.

fabless: describes a semiconductor company that doesn't have its own chip-fabrication plants (fabs). Fabless companies rely on independent foundries for manufacturing. An example of a fabless semiconductor company is Broadcom. See fab, fabrication, wafer.

fabrication: the process of manufacturing semiconductor chips. Fabrication processes are described by the smallest size of the elements they can etch into the semiconductor layer. Smaller is better, because it means the elements (mainly transistors and their connecting wires) can be packed more densely, so the chip can be smaller, which reduces manufacturing costs by fitting more chips on a wafer. Also, the chip can run at a lower voltage and/or higher clock speed while consuming less power. In the past, fabrication processes were measured in microns, such as "0.13 microns." The latest processes are measured in nanometers (nm), billionths of a meter. (0.13 microns = 130nm) For comparison, the width of a human hair is about 100 microns. See fab, fabless, wafer.

fanboy: a person (of either sex) who enthusiastically and sometimes irrationally supports a particular product, technology, company, or viewpoint. Generally not complimentary. Fanboys are like shills, but are unpaid. Sometimes spelled "fanbois."

Fast Ethernet: an upgraded version of the Ethernet networking standard that increases the maximum data-transfer speed tenfold, from 10Mbps to 100Mbps. See Ethernet.

FAT32: 32-bit file allocation table. Generically, a FAT is an index on a storage medium, usually a hard or floppy disk, a solid-state disk (SSD), a USB thumb drive, or a memory card. It keeps track of the data associated with a particular file and filename. FAT32 is a specific type of FAT that uses 32-bit addressing, which limits its maximum storage capacity to four gigabytes (4GB). It succeeded the original FAT in the MS-DOS operating system for IBM PCs that had less capacity. Newer storage schemes can address more than 4GB.

FB-DIMM: fully buffered dual-inline memory module. A next-generation standard for dynamic random-access memory (DRAM) that uses a serial connection instead of the usual parallel connection to the memory chips. The goal is to improve overall memory performance while reducing the number of pins on the input/output interface. See DRAM, parallel interface, serial interface.

FCPGA: flip-chip pin grid array, a type of packaging for microprocessors that distributes the pins in a grid over the entire bottom of the chip instead of around the periphery. It also positions the die closer to the top of the chip for more efficient cooling. Intel uses FCPGA packaging for some Pentium III and Celeron processors that fit Socket 370. Other versions of those processors use PPGA packaging, also compatible with Socket 370.

FDM: fused deposition modeling is a technology employed by some 3D printers to build objects by heating and bonding plastic filaments as the raw material. These are the most common 3D printers for consumers.

featuritis: the tendency of products to accumulate more features over time, eventually becoming too confusing for users and unmanageable for the developers. Sometimes spelled "featureitis." Also known as "feature creep" or "creeping featurism."

femtocell: a small wireless base station in a house or office building that connects cellphones to the wireless telephone network or to the Internet. Some femtocells are intended to remedy poor cellphone coverage; others provide faster Internet access. See base station, SON.

fence post bug (or fencepost bug): a programming error in which a value comparison can slightly miss the intended target. For example, a program that checks if a person has reached majority age (18 years) should include the 18th year, but a common error is to miss by one year:

   Wrong code:
   if age > 18 then majority-age = true
   Correct code:
   if age >= 18 then majority-age = true

fetch: to retrieve a program instruction or data from memory.

FIDO Alliance: Fast IDentity Online, a computer-industry consortium that's creating a safer alternative to log-in passwords. FIDO's alternative is a passkey that employs several security methods to authenticate a user's identity when logging into a device, website, or service. Passkeys for online log-ins will employ public-key cryptography.

FIFO: first in, first out. Usually refers to the order in which data enters and leaves a buffer. See FILO and LIFO.

file format: The specific way data is arranged in a file. When a word processor saves a text file, for example, it usually doesn't save only the text—it also saves formatting information. Different programs do this in different ways, which is why it's often difficult or impossible to exchange files between programs.

file server: a computer that stores files for client computers on a network. Centralized file storage is often more reliable than local file storage and makes it easier to keep track of files. See server.

FILO: first in, last out. Usually refers to the order in which data enters and leaves a buffer. See FIFO and LIFO.

FinFET: finned field-effect transistor. This new type of transistor technology began appearing in chips in the early 2010s. It builds the transistor as a vertical fin rising from the chip's flat surface and wraps the semiconductor gate partly around the conductor. This technique improves power efficiency and switching speed while allowing the transistors to be packed more closely together. FinFETs supersede planar transistors, which are etched flat on the chip's surface. By the mid-2020s, FinFETs may be superseded by gate-all-around (GAA) transistors that are even better. See gate, GAA, PPA.

firewall: a program that restricts network access, usually for security. The most common purpose of a firewall is protect a computer from unauthorized access over a network—it prevents outsiders from browsing files on the computer, deleting data, planting viruses, and other mischief. Firewalls can also restrict outgoing network access, either for security or to keep employees from using an office computer for recreational purposes. Firewalls are often built into routers.

FireWire: See IEEE-1394.

firmware: software stored in nonvolatile memory. Firmware is usually system software required to operate a digital device. Examples include the BIOS in a PC and the audio decoding/playback software in a CD player. The nonvolatile memory may be ROM or flash memory; the latter may be user-upgradable.

five nines: a measure of computer availability or reliability equal to 99.999 percent uptime, or about 53 minutes of downtime per year. See uptime, downtime.

FLAC: Free Lossless Audio Codec. A free open-source program for compressing digital audio files without sacrificing quality. FLAC is an alternative to proprietary audio-compression formats such as MP3 and AAC. See AAC, MP3, codec, open source.

flame: a text message that angrily attacks another person or point of view. Flames can be private e-mail messages exchanged between people but usually are public messages posted in online discussion groups. Flames are often considered impolite or unfair attacks.

flame war: a series of angry and often insulting messages exchanged between two or more people, usually in an online discussion group. See flame.

flash memory: a type of nonvolatile computer memory often used in thumb drives, digital cameras, digital audio players, cellphones, and other devices needing compact mass storage. Flash memory is solid-state memory that stores data in transistors. Unlike DRAM and SRAM, it retains the data even when disconnected from electrical power. The memory isn't infinitely nonvolatile, however; over time, the transistors gradually lose their charge. Popular flash-memory cards for portable storage are Secure Digital (SD), MicroSD, and Compact Flash. Older formats include the Sony Memory Stick and SmartMedia cards. See thumb drive, SSD, DRAM, SRAM.

fleeceware: computer programs or smartphone apps that quietly charge unreasonable subscription fees, usually for minimal functionality. Example: a smartphone "flashlight" app that bills the owner a monthly subscription fee, even though such apps are commonly free.

flit: part of a network packet. Typically, a packet has three flits: the header, which tells network routers where to send the packet; the payload, which contains the packet's data; and the tail, which marks the end of the packet.

floating point: a fractional number, such as 9.95 or 98.6. Computers have a more difficult time working with FP numbers than they do with integers (whole numbers), but the greater range of FP is required for some operations.

floppy: common term for a floppy disk.

floppy disk: a data-recording medium for computers. A floppy disk drive records information (programs and data) on the magnetic surface of a disk, which is similar to recording tape. Using a disk instead of tape allows random access to the data, instead of the sequential access that is characteristic of tape. Although most floppies are encased in a hard plastic shell for protection, the inner disk is a flexible magnetic material, so the term "floppy disk" still applies. Most floppies are 3.5 inches in diameter and store 1.44MB of data; SuperDisk floppies store 120MB. Older floppies were larger (5.25 and 8 inches) but stored much less data because of their lower areal densities.

FLOPS: floating-point operations per second. A common measure of performance for microprocessors and computers. One million FLOPS is one MFLOPS (megaflops); one billion FLOPS is one GFLOPS (gigaflops); one trillion FLOPS is one TFLOPS (teraflops); 1,000 trillion FLOPS is one PFLOPS (petaflops). See floating point, FPU.

folding@home is a program that runs on thousands of computers worldwide, sending results over the Internet to a remote server. A free download, the program runs in the background when a computer is idle, performing calculations for a task called protein folding. The program tries to mathematically match different simulated proteins to discover how they interact. It's the first step toward developing new medicines. Volunteers install the program on their PCs to contribute processing time to this important project. The general technique is called distributed computing, and similar programs are available for performing other tasks. See distributed computing, SETI@home.

folie à million: a delusion or fantasy shared by large numbers of people. (Coined in 2002 by Tom Halfhill) It's derived from the psychological term folie à deux, or "madness of two"—a mutually reinforced delusion shared by two unbalanced people. In the Internet age, believers of almost any fantasy or conspiracy theory can find support on a deranged website. See babble-rouser.

fondleslab, fondle-slab: slang term for a tablet computer.

foom: a hypothetical future event in which an artificially intelligent computer learns to augment its intelligence and rapidly achieves superhuman ability. The word derives from a cartoon sound effect of rapid movement. See robopocalypse, singularity, artificial intelligence, Turing test.

footprint: (1) the amount of physical space an object occupies on a flat surface; (2) the amount of storage space a program or file occupies in memory or on a disk.

forklift upgrade: an upgrade that replaces most or all of a system. An office worker who receives a new PC might describe the replacement as a forklift upgrade.

form factor: the size, shape, or physical design of an object. It's a largely useless technobabble term that can almost always be replaced with "size," "shape," or "design," or omitted altogether.

FORTRAN: FORmula TRANslator. FORTRAN is a programming language invented in the 1950s for scientific and technical computing. It excels at mathematical operations and is still used today.

foundry: an independent semiconductor manufacturer that makes chips for other companies. Vertically integrated companies like Intel have their own chip-fabrication plants (fabs), but some chip companies are "fabless" and rely on independent foundries for manufacturing. An example of a popular foundry is TSMC (Taiwan Semiconductor Manufacturing Corp.).

FP: see floating point.

FPS: first-person shooter. An electronic game in which the player directly controls a weapon that fires projectiles or energy beams; the onscreen character holding the weapon is often not seen. The graphics are usually pseudo-3D. See MMA, MMO, MOBA.

FPU: floating-point unit. A function unit in a microprocessor that executes floating-point instructions.

frame buffer: a block of memory for temporarily storing information displayed on the screen. Graphics cards usually have a large amount of fast memory for this purpose. The larger the frame buffer, the more resolution and colors a computer can display. 3D graphics cards may also store 3D objects and textures in a frame buffer.

fraudband: derogatory term for a broadband Internet connection that's slower than promised. See broadband.

frontside bus, front-side bus: the main system I/O (input/output) interface that connects a microprocessor to other system chips. Typically, it allows the main processor in a PC to communicate with the north-bridge part of the system chipset, which in turn connects to main memory (RAM), PCI devices, the AGP graphics channel, and the south-bridge part of the system chipset. The frontside bus also connects to the Level 2 (L2) cache unless the processor has a separate backside bus or integrated L2 cache. See system chipset, north bridge, south bridge, AGP, PCI, cache, RAM.

FSB: see frontside bus.

FTP: file-transfer protocol. A standard method for uploading and downloading files to and from a server over the Internet. To use FTP, the client computer needs an FTP program. The server usually has an address such as "" and often requires a registered username and password for access. "Anonymous FTP" means anyone can access the server by entering their e-mail address for the username and "anonymous" for the password. FTP is less popular these days because it's less secure and more cumbersome than other methods.

FUD: fear, uncertainty, and doubt. FUD is a marketing tactic for selling a product by instilling negative emotions about a competitor's product. Examples: "Sure, you can buy a Mac, but then you won't be able to run any software" or "Do you really want to bet your company on Linux, an operating system written by anonymous hackers?" IBM was widely considered to be the champion of FUD until succeeded by Microsoft.

FUI: (pronounced "FOO-ee") fake user interface. Derived from GUI (graphical user interface), it's a slang term for anything that pretends to be a legitimate user interface, usually for malicious or commercial purposes. Examples: the deceptive password-entry screens sometimes displayed by virus programs, or the fake error-message boxes that pop up on some websites and are actually advertisements.

FWIW: "For what it's worth...." A brief way of introducing a remark, usually in an e-mail message or online posting. See IMHO.

function: a type of subroutine that generally returns a value when called. For instance, a function named SumAnnualSales might add up a company's sales for the year and return a dollar value to the calling program or routine. See procedure, method.

function unit: a related block of circuitry in a microprocessor that executes program instructions or performs other necessary operations. There are different types of function units for different types of instructions: integer, floating point, multimedia, etc.

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GAA: gate all-around. A new, more-efficient chip-fabrication technology that wraps a transistor's semiconductor gate completely around its conductor. Starting in 2022 or 2023 with 3-nanometer (3nm) technology, GAA transistors may begin superseding FinFETs, which wrap the gate only partly around the conductor. See gate, FinFET, PPA.

gadget: a malicious attack that exploits legitimate program code. Instead of injecting new malicious code into an existing computer program, this technique forces the program to execute some existing code that can do something different than the programmer intended. Usually it works by jumping the starting point of execution into the middle of an existing routine. Sometimes it jumps into data that can be interpreted as program instructions. A technical term for gadgets is return-oriented programming. A harmless version is a code pun.

GAN: generative adversarial network. A technique that pits two machine-learning computer programs against each other to refine their learning. As they compete, each gets "smarter" at the assigned task, but only one emerges as the "smartest" winner. For example, the GANs may be programmed to play each other in chess, learning to generate better moves as they go. This technique can train an ML program with little or no human intervention. See AI, ML, deepfake.

gate: (1) the semiconducting part of a transistor that either "opens" or "closes" when a control voltage is applied or removed, thereby either allowing or blocking the flow of electricity, effectively using the transistor as an on/off switch; (2) the most basic element of logic circuits in a microprocessor. Several kinds of logic gates (AND, OR, NOR, NAND...) filter signals in different ways. Logic gates have two or more transistors.

GBps: gigabytes per second. (Billions of bytes per second.) Also abbreviated GB/s.

Gbps: gigabits per second. (Billions of bits per second.) Also abbreviated Gb/s.

GDPR: General Data Protection Regulation. A landmark European Union privacy law that took effect on May 25, 2018. It requires companies to disclose the personal information they gather on people and allow them to delete it. The law applies only to EU residents but has global implications. Some companies outside the EU voluntarily comply.

geek: someone who is technically adept but socially inept. Synonym: nerd.

generative adversarial network: see GAN.

generative AI: generative artificial intelligence — a computer program that can automatically create images, text, or music. These programs train a neural network by analyzing large amounts of the content they intend to create. Usually they harvest this content from public websites on the Internet. Examples include OpenAI's DALL-E (debut 2021) for image creation and GPT (debut 2019) for text creation. See AI, ML, neural network.

Genesis block: the first data block in a blockchain. See bitcoin, altcoin.

geometry transformation: A math-intensive process that creates the skeleton of a 3D object on a screen. It makes heavy use of floating-point numbers and matrix multiplication.

GFLOPS: giga (one billion) floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called gigaflops. See FLOPS, floating point, FPU.

GIF: Graphics Interchange Format. A once proprietary but now open file format for digital images. GIF is lossless compression—it shrinks the file without losing quality. However, it's limited to 256 colors or grays, so it's less suitable for color photos than JPEG format. Creator Stephen Wilhite (1948–2022) insisted it must be pronounced with a soft G ("jiff"). See lossless, lossy, JPEG.

gigabit: 1,024 megabits, or 2^30 bits. Abbreviated Gb. See bit, byte.

Gigabit Ethernet: an upgraded version of the Ethernet networking standard that increases the maximum data-transfer speed by 100x, to 1Gbps. See Ethernet.

gigabyte: 1,024 megabytes, or 2^30 bytes. Abbreviated G, GB, or gB. See bit, byte.

gigaflops: one billion floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called GFLOPS. See FLOPS, floating point, FPU.

GIGO: "garbage in, garbage out." The principle that feeding bad data into a computer will produce bad answers. See BIBO.

glasshole: derogatory term for someone who wears Google Glass, an early experiment in augmented-reality glasses.

glitch: a bug or a transitory malfunction in hardware or software. Often this term describes a malfunction that unlike a bug is not repeatable, or is difficult to repeat.

GNOME: (usually pronounced "Guh-NOME") GNU Network Object Model Environment. It's a graphical user interface (GUI) for the GNU/Linux operating system that provides a Windows-like desktop for file management, system maintenance, and other common tasks. See

GNU: (pronounced "guh-NOO") GNU's Not Unix. This self-referential acronym describes an operating system that looks and runs like Unix but is freely distributed by the GNU Project, which is sponsored by the Free Software Foundation. GNU is often combined with the Linux open-source kernel. GNU runs on a wide variety of microprocessor architectures.

Godwin's Law: the longer an online debate lasts, the probability that someone will make a hyperbolic comparison to Nazis or Adolf Hitler becomes almost certain. (An adage coined in 1990 by American lawyer Mike Godwin.)

gold master: programmer's term for a version of software deemed stable enough for shipment as a product. See alpha, beta, release candidate.

Googlebombing: creating web links that fool Google's Internet search engine into returning manipulated results for a particular query. Example: at one time, entering "failure" into Google returned an online biography of President George W. Bush.

Googleplex: originally, the vast server array in Silicon Valley that Google uses to index the Internet for its online search engine. Now that Google has built multiple server farms in different locations, the term often describes Google's main corporate campus in Silicon Valley. See server farm.

Gouraud shading: a method for making 3D objects in computer graphics appear naturally lighted. The computer calculates a lighting effect for each polygon vertex and interpolates the results across the entire face of the polygon.

GPIO: general-purpose I/O. Usually refers to pins on a microprocessor that are available to hardware designers for data input/output.

GPS: Global Positioning System, a method of identifying locations on Earth by triangulating signals from orbiting satellites. Originally developed for the U.S. military, GPS technology is now widely available in portable receivers for consumer applications.

GPT: Generative Pre-trained Transformer, a machine-learning program that can produce literate text. Typing a question or command into the program elicits a response that often seems humanlike. GPT is trained by scanning text on the Internet and from other sources. It's often called an "AI" (artificial intelligence), despite technical and philosophical debates over that term. GPT was created by OpenAI, a San Francisco company that has nonprofit and for-profit arms. Successive versions of GPT are numbered; GPT-3 is currently popular. See ChatGPT, AI, ML, DL.

GPU: graphics processing unit. A specialized microprocessor for graphics, especially 3D graphics. Increasingly, GPUs are also being used for other types of workloads. See GPGPU, GPU computing, HPC.

GPU computing: graphics-processing unit computing. Nvidia, a leading vendor of GPUs, uses this term to describe consumer applications other than pure graphics that run on the GPU, not on the computer's main CPU. GPU computing is the consumer counterpart to professional GPGPU computing. See CPU, GPU, GPGPU.

GPGPU: general-purpose graphics processing unit. This term describes the execution of high-end scientific, engineering, and financial computing on a GPU, not on the computer's main CPU. See CPU, GPU, GPU computing, HPC.

graphics: images displayed or printed by a computer. They may be animated or static, color or monochrome. Modern graphics almost always consist of individually addressable pixels, but many older computers drew images with special characters. See graphics card, graphics chip, pixel.

graphics card: a circuit board that contains a graphics processor and memory chips. Usually, the board plugs into a slot inside a computer and handles many of the processing tasks required to display graphics on the screen. The graphics card accelerates those tasks by assisting the CPU. See AGP, CPU, graphics, graphics chip, memory.

graphics chip: a special processor that helps a computer draw graphics on the screen. The computer's CPU offloads many data-intensive tasks to the optimized graphics processor, which is also known as a graphics coprocessor or accelerator. See AGP, coprocessor, CPU, graphics, graphics card.

Great Firewall of China: an Internet-level firewall operated by the Chinese government that blocks foreign content deemed unacceptable. Censored content includes political, social, and historical information as well as pornography. See firewall.

griefers: people who amuse themselves by interfering with the operation of online games, causing grief for legitimate players.

Grover's algorithm: a mathematical formula that theoretically can break AES encryption when executed on a quantum computer. The algorithm effectively halves the security of the AES key length, so AES-128 becomes as easy to crack as AES-64. Experts say AES-256 provides enough security to foil even a quantum-computer attack. See AES, quantum computing, Shor's algorithm.

GUI: (pronounced "GOO-ee") graphical user interface. The windows, buttons, menus, scrollbars, and other graphical screen elements that allow a user to control a computer program. See command-line interface, user interface, skin.

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hack: (verb) to work on a computer or program, sometimes with malicious intent, or (noun) a crude solution to a problem with a computer or program. Example (verb): "Someone tried to hack into our network." Example (noun): "I fixed the problem for now, but it's a hack." See hacker, hacktivist.

hack-back company: a private-sector company for hire that will retaliate against malicious hackers by attacking their computers. It's not always legal, and often the true source of the original attack is hard to identify. See hacker, hacktivist, black-hat hackers, white-hat hackers, pen tester.

hacker: originally any skilled person who enjoyed tinkering with computers. Now the term usually refers to people who maliciously attempt to break the security of a network or computer. Such black-hat hackers may be countered by good white-hat hackers. See pen tester.

hacktivist: a "hacker-activist"—a hacker who inflicts damage on computers, networks, or websites not for personal gain, but supposedly for a political or social cause. An example are the hacktivists who use denial-of-service attacks to disable the websites of multinational corporations and international trade organizations.

hamburger: a small icon comprising three horizontal lines that opens a menu of options when clicked. Hamburgers are often located near a top corner of the screen. The three horizontal lines vaguely resemble a hamburger with two buns enclosing a beef patty.

hard disk: a rewritable mass-storage device that uses a magnetic recording surface on a hard metal platter. Modern hard disk drives have several platters that spin at 3,600 to 7,200 rpm or even faster. The drive stores information (programs and data) on the platters for fast retrieval. A hard disk is usually built inside a computer and isn't removable without tools; sometimes it's called a fixed disk. See ATA, EIDE, IDE, Serial ATA.

hard drive: see hard disk.

HD: High Definition. An international video standard that has more screen resolution than the first-generation standards used for television since the 1930s. HD resolution may vary, but the most common formats are 1,280 x 720 pixels and 1,920 x 1,080 pixels. See UHDTV, 4K, pixel, aspect ratio.

HD-AAC: High-Definition Advanced Audio Coding. A new method of compressing digital music that attempts to retain full fidelity without compromising quality. HD-AAC was developed by Fraunhofer, the German company that also developed the MP3 codec. HD-AAC is backward compatible with AAC, the compression method commonly used on the Apple iPod. See AAC, codec, lossy, MP3, FLAC.

HD-DVD: High-Definition Digital Versatile Disc. (Also abbreviated HD DVD.) An optical-disc format that greatly increases the capacity of DVD-size (4.75-inch) discs. It uses blue lasers, whose shorter-wavelength light allows more data to be recorded in the same space. (Ordinary DVDs and CDs use red lasers.) Also, HD-DVD records data in multiple layers. Maximum available capacity is 30GB. Can be used to store video or computer data. HD-DVD has enough capacity and speed for HD video. However, in a format war that essentially ended in 2008, HD-DVD was defeated by its rival, Blu-ray. See Blu-ray, HD.

HDD: hard disk drive. A mass-storage device that stores data on one or more spinning-metal magnetic disks. An electromagnetic read/write head suspended just above the disk surface reads and writes the data. HDDs are the most common mass-storage devices in computers, although they are gradually being replaced by faster SSDs.

HDMI: High-Definition Multimedia Interface. A digital input/output interface for transferring audio and video data over relatively short cables. Most previous standards were analog, not digital, although the data was usually converted to and from a digital format. HDMI is appearing on TVs as well as computers.

HDTV: High-Definition Television. See HD.

head crash: a disastrous event in which a read/write head of a hard disk drive falls out of alignment and collides with the surface of a spinning platter. It almost always damages the head and the platter, resulting in lost data.

headless: (1) a server without a video monitor, keyboard, and mouse, or (2) software lacking a graphical user interface (GUI) because it's designed to run on such a server. Large installations often share a monitor among several servers. Once a server is properly configured and running, it usually doesn't need a monitor, except for occasional maintenance. See server, GUI.

heat sink: a structure that draws heat away from an electrical device. Heat sinks often have fins to radiate heat more efficiently. They are commonly used on modern CPU chips.

HEDT: high-end desktop (computer); a high-performance PC.

hello world: a simple example program that demonstrates the basic requirements of a new programming language, programming tool, or software platform. The program usually prints "Hello, world!" on the screen, but it can be any introductory example.

Herzberg-Wood, Elaine Marie: the first person killed by an autonomous vehicle. Herzberg-Wood was walking her bicycle across a street in Tempe, Arizona on the night of March 18, 2018 when she was fatally struck by an Uber self-driving car. Uber's computer navigation system had trouble identifying the 49-year-old woman and her bicycle, and it sounded a collision warning too late for the Uber safety driver to seize control and brake manually. Also, Uber had disabled Audi's factory-installed collision-avoidance system to prevent interference with Uber's own system. This accident was a major setback for the adoption of autonomous vehicles.

hexadecimal: a base-16 number system used in computer programming. There are 16 digits—0 through 9 plus A, B, C, D, and E. Hexadecimal 10 equals decimal 16. Programmers use hexadecimal numbers to represent binary numbers in a more compact form.

HFT: high-frequency trading. Financial trading in stocks, bonds, commodities, currencies, or other assets in which a computer algorithm makes the buy and sell decisions. These programs operate at very high speeds, sometimes buying and selling large volumes of an asset within a few seconds, making small profits that add up to large sums over time.

HKMG: high-k metal gate. It's a more power-efficient transistor gate; not to be confused with logic gates. Essentially, a transistor gate is the "on/off switch" that determines if electricity flows through the transistor. Until recently, these gates used a silicon dioxide insulator. Newer technology, first used in mass production by Intel, substitutes an exotic metal alloy that includes hafnium. This material reduces current leakage when the gate is "off," thereby improving power efficiency. The term k is the dielectric constant, or insulating value of the material. Higher k means better insulation.

HMAC: hash-based message-authentication code. A secure method for authenticating an encrypted message with a digital signature. See MAC, SHA.

HomeRF: a wireless local-area network (WLAN) standard, primarily for home use. HomeRF WLANs operate in the 2.4GHz radio-frequency band and can carry both voice and data traffic. The data-transfer rate is 1Mbps to 2Mbps. A future version will hit 10Mbps, making it more competitive with IEEE 802.11b; the two standards are incompatible. See LAN, 802.11.

honeypot: a networked computer designed to trap malicious hackers. The honeypot computer—often left deliberately vulnerable—diverts the hacker's attention away from other computers on the network and allows administrators to intercept and possibly trace the hacker's communications.

hot plugging: the ability to attach or detach devices on an interface without turning off their power and without causing damage. Interfaces that support hot plugging also have software that recognizes the arrival of a new device and allows it to function without rebooting the computer. USB and FireWire are examples of interfaces with hot plugging.

hot spot or hotspot: (1) an access point for a wireless network; (2) a critical section of a computer program that can be accelerated by optimizing the program code. See 802.11, warchalking, Wi-Fi, WLAN.

HPC: high-performance computing. This seemingly general term actually is specific to high-end scientific, engineering, and financial computing, usually on a supercomputer. Also popular are "desktop supercomputers" that use arrays of graphics cards for general-purpose processing. See GPU, GPGPU, GPU computing.

HTML: hypertext markup language, a standard set of tags that defines how the contents of a web page should appear in a web browser. Most tags describe the appearance of text and the position of graphics. HTML standards are defined by a committee called the W3C (World Wide Web Consortium).

HTTP: hypertext transfer protocol, the industry standard for sending pages of text and graphics over the World Wide Web from servers to personal computers. It allows pages to link to other pages containing related material.

hub: a network device that joins cables together, often for the purpose of attaching additional devices to the network.

HUMA: heterogeneous unified memory access. A system architecture that allows different kinds of processors to share the same memory space. For example, the main microprocessor in a PC can share memory with the graphics processor.

hype coin: a digital-only currency or commodity that has no intrinsic worth; it tries to build value solely on clever promotion and public mania. See idiot coin, cryptocurrency, bitcoin.

hyperlink: a reference from one web page to another, or from one location of a web page to another location on the same page. Also known as hypertext. Users can click on a hyperlink to view the referenced page or location. The hyperlink is encoded in HTML, a formatting language for web pages, and uses HTTP, a file-transfer protocol for web pages. For example, the following HTML hyperlink points to the home page of this website: Tom's home page. Here's what the HTML formatting looks like:

<A HREF="">Tom's home page</A>

Hyper-Pipeline, hyperpipeline: Intel's term for the unusually deep superpipeline in the Pentium 4. See superpipeline.

hypertext: text on a computer screen that points to some other text or graphics stored elsewhere on the same computer or on a network. Hypertext provides a "live reference"--clicking on the hypertext automatically displays the referenced text or graphics. See hyperlink, HTML, HTTP, Internet, World Wide Web.

HyperTransport: an internal system bus for PCs developed by AMD and API Networks. HyperTransport is a serial-link bus that supports widths of 4, 8, 16, and 32 bits and data-transfer rates up to 12.8 gigabytes per second. It is backward compatible with PCI. See PCI, 3GIO, ISA.

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I-cache: see instruction cache.

i-Mode: a proprietary wireless data protocol from NTT DoCoMo (Nippon Telegraph and Telephone Mobile Communications Network Inc., Japan). Based on CompactHTML, i-Mode allows mobile phones, pagers, PDAs, and other wireless communication devices to access special content on the Internet. A competing protocol is WAP.

I/O: input/output. See interface.

IA-64: Intel Architecture 64, a 64-bit microprocessor architecture owned by Intel. It's based on a design philosophy called EPIC (explicitly parallel instruction computing) created in partnership with Hewlett-Packard; EPIC, in turn, is based on VLIW. Intel designed IA-64 as the eventual successor to the x86 architecture. The first IA-64 processor was code-named Merced and is now known as Itanium.

IC: integrated circuit. A single piece of semiconducting material (usually silicon) that has multiple components (usually transistors).

ICO: initial coin offering. ICO is a play on "IPO" (initial public offering), which describes the first public issue of stock in a company. An ICO is the first public issue of a new cryptocurrency, such as bitcoin.

IDE: Integrated Device Electronics, an industry-standard I/O interface for connecting disk drives to PCs. IDE is a parallel-type interface that uses 40- or 80-wire ribbon cables. An IDE interface can handle two devices, known as the master and the slave. Most PCs have two IDE interfaces, known as the primary IDE and secondary IDE. This permits a total of four IDE devices. Modern PCs use EIDE (Enhanced IDE), which is faster than the original IDE standard. The Ultra ATA-66, ATA-100, and ATA-133 standards require an 80-pin EIDE interface.

idiot coin: a cryptocurrency or "hype coin" created in 2021 by reporter David Segal for a New York Times story on cryptocurrency mania. Although he intended to show how easily someone can create a worthless digital commodity, he caused a minor sensation that boosted the liquidity pool's initial $30 value to more than $100,000. The experiment actually showed how easily someone can create an intrinsically worthless but nevertheless valuable commodity. See hype coin, cryptocurrency, bitcoin.

IEEE: Institute of Electrical and Electronics Engineers. IEEE (pronounced "eye-triple-E") is an international association for engineers, scientists, programmers, doctors, and some other professionals. Founded in 1884 as the American Institute of Electrical Engineers, in 1963 it merged with the Institute of Radio Engineers, which was founded in 1912. Among other things, IEEE adopts technical standards, such as the 802.11 series for Wi-Fi wireless networking.

IEEE-1394: a high-speed serial peripheral interface for hooking up disk drives, digital-video cameras, and other devices to computers and to each other. Apple invented the technology and calls it FireWire. (Sony calls it iLink.) In 1995 it was adopted as a standard by IEEE, an industry organization. The IEEE-1394a standard allows data-transfer rates of 100, 200, and 400Mbps. The future 1394b standard will scale to 800Mbps and higher rates.

iLink: Sony's brand name for the IEEE-1394 interface, also known as FireWire.

IM: instant messaging. A service that allows people to send brief text messages that instantly appear in a small window on the recipient's computer screen.

IMAP: Internet Message Access Protocol, a worldwide standard that defines how computers can retrieve e-mail stored on mail servers. IMAP is a popular standard supported by most mail clients, including Microsoft Outlook, Netscape Messenger, and Eudora. Another standard is POP3.

IMHO: "In my humble opinion...." A brief way of introducing a remark, usually in an e-mail message or online posting. See FWIW.

INABIAF: "It's not a bug, it's a feature." This expression, which dates at least to the 1980s, is a common excuse that programmers and engineers use to explain unexpected behavior in their creations. It implies that the behavior is actually useful or at least unharmful. The expression is often delivered tongue-in-cheek.

infinite loop: a programming error that causes the computer to circle endlessly through the same sequence of program instructions. Sometimes there's no escape but to force the program or even the whole computer to shut down.

ink-jet printer: a computer peripheral that prints text and graphics by depositing tiny droplets of ink on the paper or other printing material.

instruction cache: a block of extra-fast memory on a microprocessor chip that temporarily holds instructions for a running program. The processor fetches instructions into the cache from main memory so they are immediately available when the program needs them. This saves time because cache memory (SRAM) responds much faster than main memory (DRAM). If the program cannot find the instructions it needs in the cache, it "flushes" part of the cache and reloads it with the required instructions from main memory.

instruction parallelism: performing a large task by reducing it to smaller streams of program instructions that a computer can process simultaneously. Instruction parallelism can yield huge gains in performance. However, it may require special programming, and not all tasks can be reduced in this manner. See program, data parallelism, massively parallel.

instruction set: the program instructions a microprocessor can execute. Different microprocessor architectures have different instruction sets, which is why they usually can't run the same software. See ISA.

integer: A whole number, such as 1, 2, 3, etc. Computers can manipulate integers much faster than they can manipulate floating-point numbers (fractions), but floating-point numbers have greater dynamic range.

integration: adding more functions to a chip. Over time, advances in manufacturing technology make it possible to squeeze more transistors onto a silicon chip. Engineers can use those transistors to add more functionality. Devices that used to be built as separate chips can be combined into a single chip.

interconnect layers: metal layers in a silicon chip that wire the transistors together. Chips may have several interconnect layers made of aluminum, but the most advanced processors have faster layers made of copper.

interface: a connection between two or more electronic devices, usually for transferring data. There are many different kinds of interfaces for different purposes.

Internet: a worldwide network of computer networks based on the TCP/IP standard. Originally created by the U.S. Department of Defense to link networks at government installations and universities, the Internet evolved into a worldwide commercial network in the 1990s. The World Wide Web uses the Internet to transmit hyperlinked pages of text and graphics using HTTP. See HTTP, TCP/IP, network, newsgroup, World Wide Web.

Internet of Things: Usually abbreviated IoT, it's the concept of attaching virtually any electronic device to the Internet for the purposes of remote control, firmware updates, or data collection. Examples: sensors, thermostats, light switches, appliances, alarms, webcams, vehicles, etc. Some IoT devices may not interact directly with people—they may perform machine-to-machine (M2M) interactions.

interrupt: a signal or instruction that causes a microprocessor to respond to new input, usually by executing a different instruction stream. See context switch, determinism.

intranet: a restricted-access network based on the TCP/IP standard. Users access the network with a web browser, as they do with the World Wide Web, but access usually requires a password available only to the employees of a company or some other group of people.

I/O: input/output. Sending and receiving electrical signals, which usually carry data.

IoT: see Internet of Things.

IP: (1) Internet Protocol; (2) intellectual property. Internet Protocol is a low-level standard for transferring packets of data over the Internet. Intellectual property is proprietary hardware, software, or content that may be protected by patents or copyrights.

IP address: Internet Protocol address. A 32-bit (IPv4) or 128-bit (IPv6) number that identifies a computer on a TCP/IP network, such as the Internet. Computers use IP addresses to exchange data; for example, the address tells a web server which PC on the Internet requested a web page. Every computer attached to the Internet needs a unique IP address, although it's common for computers on a local-area network (LAN) to share external IP addresses through a router or proxy server. See Internet, LAN, DNS, proxy server, router, TCP/IP.

IPC: instructions per cycle. A measure of efficiency for microprocessors; the higher the IPC, the better.

IRC: Internet relay chat. A protocol that uses the Internet for real-time text-only chat sessions between users.

IRL: in real life. An abbreviation often used online to describe offline life.

ISA: (1) instruction-set architecture; (2) Industry Standard Architecture. The first term refers to the distinguishing characteristics of a microprocessor architecture, such as the instruction set, register file, and byte ordering. The second term refers to an internal system bus for PCs that IBM introduced in 1981. It was also known as the XT bus or AT bus (named after early IBM PCs). The ISA bus was upgraded to EISA (Extended ISA) and later supplanted by PCI. See EISA, PCI, PCI Express.

ISDN: integrated services digital network. A telephony service that allows a computer to access the Internet over ordinary phone lines at higher speeds than regular analog modems. ISDN modems transmit and receive middleband digital signals over phone lines without interfering with voice communications. Transmission speeds are usually 56Kbps to 128Kbps.

iSIM: integrated subscriber identity module. The virtual equivalent of a SIM card built into a mobile phone or other electronic device instead of using a removable SIM card in a slot. Future mobile phones will probably use iSIMs instead of SIMs. They are also useful in small devices, such as smartwatches. See SIM.

ISP: Internet service provider. A company that provides access to the Internet. In the U.S., a monthly fee of $20-$25 usually buys unlimited dial-up access over ordinary telephone lines. See ADSL, broadband, cable modem, DSL, Internet, modem.

Itanic: derogatory name for Intel's Itanium processor, code-named Merced. Derived from "Itanium" and "Titanic." (Coined in 1999 by Kraig Finstad)

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j-mail: unwanted e-mail, usually mass-mailed advertising. "J-mail" is derived from "junk mail" and is more commonly known as spam. ("J-mail" was coined in the 1980s by Arlan Levitan)

jaggies: the visibly jagged edges of pixels in a digital image, especially apparent when viewing the square or rectangular pixels along the edge of a curved line. Smaller pixels (higher resolution) is the cure; anti-aliasing helps, too. The jaggy effect is also called "staircasing." See anti-aliasing, pixel.

jailbreak, jailbreaking: to unlock a smartphone so it can download and run apps from sources other than the vendor's official app store. The security risk is greater because the unofficial apps may contain malware or spyware, but the user has more freedom to install software. The unlocked phone is said to be jailbroken.

Java: an object-oriented programming language introduced in 1995 by Sun Microsystems. It has strong support for networking. It's also unusual in that it's a virtual platform as well as a language—programs written in Java can run on many different computers without porting or recompiling.

JavaScript: a web-page scripting language invented by Netscape Communications. Originally called LiveScript, it bears only a superficial resemblance to the Java programming language. JavaScript mainly adds functionality to HTML forms and other types of web pages. See AJAX, HTML.

JIT: just-in-time compiler. Often used with Java, it's a compiler that converts some form of intermediate program code into object code that a native platform can execute. The JIT compiler translates the code when the program runs—in contrast to a regular compiler, which programmers use during development.

JPEG: Joint Photographic Experts Group. An international organization that defines standards for digital photography. In general usage, JPEG refers not to the organization but to a popular file format for digital images. Almost all digital cameras use JPEG. It's a lossy compression format, meaning it sacrifices some image quality to reduce the file size. See lossy, lossless, codec.

jumper: an electrical connection that closes a circuit, usually to enable some function in a computer device. It's really a crude on/off switch. Some motherboards and disk drives in PCs have jumpers for adjusting configuration settings.

********** K **********

K7: AMD's code name for the Athlon x86-compatible microprocessor. See Athlon.

Katmai: Intel's code name for Pentium III, a P6-series x86 microprocessor chip introduced in March 1999. Pentium III was the first chip to include SSE (Streaming SIMD Extensions), 70 new instructions for speeding up 3D graphics and other operations.

KBps: kilobytes per second. Don't confuse with Kbps.

Kbps: kilobits per second. Don't confuse with KBps.

KDE: K Desktop Environment. (The "K" doesn't stand for anything.) A graphical user interface (GUI) for Linux that provides a Windows-like desktop for file management, system maintenance, and other common tasks.

kernel: a low-level component of an operating system that's primarily responsible for allocating the computer's resources, such as memory. An example of a kernel is Linux.

killer app: an application so compelling that it alone justifies the purchase of a computer or establishes a new computer platform. Spreadsheet programs were the killer app for early IBM-compatible PCs; desktop publishing was the killer app for the Macintosh.

kilobit: 1,024 (2^10) bits. Abbreviated Kb. See bit, byte.

kilobyte: 1,024 (2^10) bytes. Abbreviated K, KB, or kB. See byte.

kludge: (pronounced "klooj") a poor or overcomplicated design. Among geeks, to say that a program or a hardware device is a kludge or kludgy is an insult. Antonym: elegant.

KNI: Katmai new instructions, the prerelease code name for SSE. These are the 70 new instructions introduced by Intel in the Pentium III processor that was known as Katmai before its release in March 1999. The new instructions accelerate 3D graphics and other multimedia tasks. KNI also adds eight new registers to the x86 architecture.

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L1 cache: see Level 1 cache.

L2 cache: see Level 2 cache.

L3 cache: see Level 3 cache.

LAN: local-area network. A private computer network within a building or group of buildings. Most LANs are wired with cables hidden in walls and ceilings, although wireless connections are also available.

LAN party: a social gathering in which everyone brings a computer and hooks the machines together in a temporary network, usually to run a multiplayer computer game.

laser printer: a computer peripheral that prints text and graphics by using the heat of a laser to bond finely ground powder with the paper or other printing material.

LCD: liquid-crystal display. This technology uses the liquid state of some crystalline structures to form monochrome or color images on a flat-panel screen. There are many variations of LCD technology.

legacy code: existing computer software that's important enough for programmers to maintain or that new computer hardware must run, despite the software's age and shortcomings. Often viewed as a burden for new technology. See dusty deck.

Level 0 cache: a small prefetch cache preceding the Level 1 cache of a microprocessor. Historically, registers were considered L0 cache, but lately, some engineers refer to a supplemental L1 cache as "L0 cache."

Level 1 cache: the fastest cache memory available to a microprocessor. It consists of on-chip SRAM cells. Also known as primary cache.

Level 2 cache: the second-fastest memory available to a microprocessor (second only to the Level 1 cache). It may consist of SRAM chips near the processor, although many recent processors have on-chip L2 caches. Also known as secondary cache.

Level 3 cache: the third-fastest memory available to a microprocessor (following the Level 1 and Level 2 caches). L3 cache is less common, but when it's present, it usually consists of SRAM chips near the processor. However, some processors have integrated on-chip L3 caches. See LLC.

LIFO: last in, first out. Usually refers to the order in which data enters and leaves a buffer. See FIFO and FILO.

link rot: the expiration of World Wide Web hyperlinks. Links to web pages never really expire due to age but often lead nowhere when a website manager changes a target page's address without updating all the links to that page.

Linux: (pronounced "LIN-icks") a kernel for the GNU/Linux operating system that looks and runs much like the historic Unix operating system but is written in free open-source program code. It was created in 1991 by Finnish college student Linus Torvalds (now an American citizen), who continues to supervise its development. Linux runs on many different microprocessor architectures. The Linux kernel has spawned numerous versions ("distributions" or "distros") of the operating system, such as Debian, Ubuntu, Mint, Red Hat Enterprise, SUSE, Slackware, Arch, Fedora, Chromium OS, and Chrome OS. See GNU, kernel, Unix.

Lisa: a personal computer introduced by Apple in 1983 that was the first attempt to popularize the graphical user interface (GUI). Although the Lisa was a groundbreaking computer, it was expensive and underpowered, and it never achieved widespread success. A year later, Apple introduced the Macintosh, which was somewhat less powerful than the Lisa but much less expensive. The Mac improved on the Lisa's GUI and succeeded in establishing the GUI as the dominant user interface for personal computers.

listicle: an attention-grabbing "news story" consisting mainly or solely of a list of superficial items. Listicles usually lure readers to a website that has lots of advertising. Example listicle: "The 10 Ugliest Celebrities." See clickbait.

little endian, little-endian: a multibyte value that begins with the least significant byte (LSB) stored at the lowest memory address. The opposite is big endian. Microprocessors are either big endian or little endian, depending on how they store multibyte values. For example, the Intel x86 architecture is little endian. Some architectures can handle both formats and are bi-endian.

LLC or LL cache: last-level cache. The highest-level cache in the memory hierarchy of a microprocessor. The lowest-level cache is closest to the processor core and is usually called Level 1 cache; many modern processors also have Level 2 and Level 3 caches. In this case, the L3 cache would be the LLC. See cache, Level 1, Level 2, Level 3.

LOL: "laughing out loud." A brief response to a humorous e-mail message or online posting. See ROFL.

LON: LAN-on-motherboard. A motherboard with an integrated network interface, so a network interface card (NIC) isn't required. See LAN, motherboard, network, NIC.

LongHaul: a power-saving feature of some VIA x86 microprocessors. LongHaul saves power by automatically reducing the chip's supply voltage and clock frequency when the demand for processing power is low. LongHaul automatically raises the voltage and frequency when the demand for performance is higher. See LongRun, PowerNow, SpeedStep.

LongRun: an innovative power-saving feature pioneered by Transmeta's microprocessors. LongRun saves power by automatically reducing the chip's supply voltage and clock frequency when the demand for processing power is low. LongRun automatically raises the voltage and frequency when the demand for performance is higher. See LongHaul, PowerNow, SpeedStep.

look and feel: the visual appearance and operation of a graphical user interface (GUI). There are several styles of GUIs, such as Microsoft Windows, the Macintosh, Motif (for Unix), etc.

loop: a programming structure that repeatedly executes one or more program statements a specified number of times or until a certain condition is met. Almost all programming languages have multiple ways of creating loops.

loot box: a virtual container in an electronic game that may contain objects for use in the game. The objects may be tools, weapons, garments, or even magic spells. Usually, the contents are unknown until the player opens the box. In some games, players must pay virtual cash or real money before discovering the contents; critics say it's like online gambling.

lossless: describes a method of compressing digital data (usually audio, video, or graphics) that preserves the original quality of the data. Examples of popular lossless compression methods are GIF and TIFF (for graphics) and FLAC (for audio). See lossy, codec, GIF, JPEG, AAC, MP3.

lossy: describes a method of compressing digital data (usually audio, video, or graphics) that sacrifices some quality to achieve greater compression. Examples of popular lossy compression methods are AAC and MP3 (for audio) and JPEG (for graphics). See lossless, codec, AAC, MP3, JPEG.

LSB: least significant byte or bit. In a multibyte value, it's the byte that has less value than the next most significant byte (MSB). The position of the LSB depends on whether the architecture is little endian or big endian. Within a byte, the least significant bit is the rightmost bit.

LTE: Long-Term Evolution. A fourth-generation (4G) cellular telephony standard.

lurker: someone who reads messages posted in an online forum, but who never posts.

luser: (pronounced "loser") derogatory term for computer users, sometimes used by programmers who have a low opinion of the people who use their software.

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M2M: machine-to-machine. Interactions between two network-attached devices without human intervention. See Internet of Things.

MAC: (1) Macintosh; (2) multiply-accummulate; (3) media-access controller; (4) message-authentication code. (1) is an incorrect abbreviation of "Macintosh," which more properly should be lowercase. (2) refers to the MAC instructions that digital-signal processors and some microprocessors use to multiply and add numbers together in a single operation. (3) is a chip (or part of a chip) that allows a computer to communicate over an interface with a peripheral or network. (4) is a secure method of indicating that an encrypted message originated from an authorized sender. See HMAC, SHA.

Mac: abbreviation of "Macintosh."

Mac OS X: Macintosh Operating System Ten. It is the current version of the Apple Macintosh operating system, which was originally shipped with the first Macintosh in January 1984. Mac OS has undergone significant changes over the years, including ports from the Motorola 68000 microprocessor architecture to the PowerPC architecture to the Intel x86 architecture. Mac OS X made its debut on servers in 1999 and on desktop and notebook computers in 2001. Recent versions of Mac OS X were nicknamed "Tiger" (10.4), "Leopard" (10.5), "Snow Leopard" (10.6), "Lion" (10.7), "Mountain Lion" (10.8), "Mavericks" (10.9), "Yosemite" (10.10), and "El Capitan" (10.11). The latest version is "Sierra" (10.12), released in September 2016.

machine code: the actual program code a computer executes. Programmers write in source code, which a compiler converts into machine code (also called object code, executable code, or binary code). Machine code is specific to a particular microprocessor architecture, so a program compiled for an x86 processor won't run on a PowerPC processor or vice versa.

Macintosh: a personal-computer platform introduced by Apple in 1984. The Mac was the first popular platform with a graphical operating system. Although based on Apple's earlier Lisa and some computers built at Xerox PARC (Palo Alto Research Center), the Mac was a highly original design that pioneered many new features. The first Macs used Motorola 68000-family processors; in 1994, Apple introduced the first Power Macs using IBM/Motorola PowerPC processors, while retaining backward compatibility with 68000 software. Apple tried licensing the Mac platform to other companies in the 1990s, but later discontinued the licenses and is once again the only supplier of Macs. In 2006, Apple switched microprocessor architectures again, this time to the Intel x86.

macro: a script of commands that automatically carries out a series of tasks. Macros typically automate repetitive tasks in spreadsheet programs, database programs, word processors, and other types of software. They are really small programs.

macrocell: see base station.

mainboard: another term for motherboard. Mainboard seems to be the more popular term outside the USA. Apple refers to Macintosh motherboards as the "main logic board."

mainframe: a large computer designed for running a sizable business or organization. Traditional mainframes filled entire rooms and were built with expensive custom components. Today's mainframes are usually smaller and built with off-the-shelf chips, including microprocessors. Often, modern mainframes are called enterprise servers. Larger machines designed for heavy-duty number crunching are called supercomputers. See microprocessor, minicomputer, supercomputer.

malware: malicious software. See APT, cracker, hacker, phishing, spear phishing, virus, worm, Trojan horse, spoof, zombie.

manycore: a chip design that integrates many microprocessor cores on a single chip. A manycore chip has more processor cores than a multicore chip, but fewer cores than a massively parallel chip. There is no hard rule, but a chip with 16 or more cores may be described as a manycore design. See multicore, microprocessor, massively parallel.

massively parallel: a type of computer design that coordinates numerous microprocessors to perform a single task. The task must be reducible to pieces that can execute independently (or nearly so) on the microprocessors. There is no hard rule, but a system with at least 64 microprocessors operating in parallel may be called a massively parallel computer. Sometimes, the microprocessor cores are integrated on a single chip to create a massively parallel processor. See multicore, manycore, supercomputer, microprocessor, data parallelism, instruction parallelism.

matrix multiplication: A mathematical process, commonly used by 3D graphics programs, in which the computer multiplies and adds two sets of numbers together. One set is the coordinate matrix and the other set is the transform matrix. The result of matrix multiplication is a new coordinate matrix.

MBps: megabytes per second. Don't confuse with Mbps.

Mbps: megabits per second. Don't confuse with MBps.

meatspace: slang term for the real world, as opposed to cyberspace.

megabit: 1,024 kilobits, or 2^20 bits. Abbreviated Mb. See bit, byte.

megabyte: 1,024 kilobytes, or 2^20 bytes. Abbreviated M, MB, or mB. See bit, byte.

megaflops: one million floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called MFLOPS. See FLOPS, floating point, FPU.

megapixel: one million pixels. It's commonly used to describe the resolution of digital cameras. If the camera's sensor can resolve at least one million pixels (for example, 1280 x 1024), then it's a megapixel camera. The more pixels, the more detailed the image.

memory: in the broad sense this term can describe any data-storage device for a computer system, but usually it refers to the memory chips that temporarily store programs and data while the computer is running. Most memory is volatile, so the system needs some form of mass storage to permanently store programs and data files, which are copied into memory on demand. See RAM, DRAM, SRAM, RDRAM, volatile.

metadata: data that describes data. For example, digital cameras automatically save data about the pictures they take—exposure information, the camera type, lens focal length, date/time, etc. This metadata describes the image data.

metalanguage: A language for designing other languages. XML is an example of a metalanguage for designing document markup languages. It's derived from SGML, a more complete metalanguage.

metaverse: an online community or virtual world in which graphical avatars represent the participants. Usually, people choose their avatars, which may depict full-body humans, just faces, or even animals and other nonhuman objects. Avatars may be able to communicate with other avatars by text or voice messages. Some metaverses allow the avatars to roam the virtual world and interact with its elements, much as people do in the real world. The term "metaverse" originates from Neal Stephenson's 1992 science-fiction novel Snow Crash, but the concept first appeared in Habitat, a massively multiplayer online role-playing game developed in 1985. LucasFilm Games tested the program in 1986–1988 on Quantum Link, an online service that later became America Online (AOL); a downsized version called Club Caribe followed. In October 2021, Facebook CEO Mark Zuckerberg announced that the company was changing its name to Meta and would soon launch a new metaverse social-media platform. See avatar.

method: a subroutine in object-oriented languages. Objects have methods that perform tasks. An object named Circle might have methods named draw (which draws a circle on the screen) and fill (which fills the circle with color). The instruction Circle.draw() would call the Circle object's draw method. See function, procedure.

metrocell: see base station.

MFLOPS: one million floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called megaflops. See FLOPS, floating point, FPU.

MFP: multifunction printer. A computer printer that can additionally serve as a flatbed scanner, photocopier, and fax machine. Also known as an AIO printer.

memory controller: a chip (or part of a chip) that manages the interface between a microprocessor and main memory.

Micro-ATX: an industry-standard motherboard (main circuit board) for personal computers. Measuring 9.6 x 9.6 inches, Micro-ATX motherboards are typically found in desktop computers smaller than full-size PCs, which typically have ATX motherboards. See ATX, Mini-ITX, motherboard, mainboard.

micro-op: short for micro-operation. Some microprocessors internally convert their complex instructions into simpler ones that execute more efficiently. For example, an instruction that adds two numbers and stores the result in main memory is typically broken into a pair of micro-ops—one for the addition and another for the store. Memory operations are slower, so the processor may be able to execute other instructions while waiting for the store to complete. Processors that have a complex instruction-set computing (CISC) architecture are the most likely to use micro-ops. Almost all x86 processors since the late 1990s employ them. See microprocessor, architecture, CISC, RISC, x86.

microarchitecture: the internal design of a microprocessor. Not to be confused with the processor's architecture, which defines its compatibility. Two chips with different microarchitectures but the same architecture can run the same software.

microcell: see base station.

microcomputer: a computer based on a microprocessor chip; usually a personal computer. "Microcomputer" was a popular term in the 1970s and early 1980s because it distinguished microprocessor-based computers from their larger minicomputer and mainframe-computer brethren. By the late 1980s, the term gave way to "personal computer" (or simply "PC") and is rarely used today. See microprocessor, PC, minicomputer, mainframe.

microcontroller: a microprocessor for embedded systems that typically has on-chip memory and peripherals. It some cases a microcontroller can function as a self-contained system without additional chips. Microcontrollers are commonly found in non-PC devices, such as appliances, industrial machines, and vehicles. Often, they are based on older CPUs no longer considered powerful enough for PCs.

microprocessor: the primary chip that performs arithmetic and logical functions in a computer. It executes program instructions and stores results in memory. All other chips basically assist the microprocessor; for instance, memory chips store the program instructions and data that the processor manipulates. See architecture, CPU, microarchitecture, microcontroller.

microprocessor core: (1) the central part of a microprocessor chip that carries out program instructions; (2) a microprocessor design ready for integration on a chip, usually in combination with other components, such as peripherals and memory. The first term generally refers to a CPU's microarchitecture; the second term refers to licensable IP (intellectual property).

microSD: micro Secure Digital. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. MicroSD is a physically smaller version of the SD card standard (11mm x 15mm x 2.1mm instead of 24mm x 32mm x 2.1mm). It's designed for cellphones and other small devices. MicroSD cards are slower and usually have less capacity than full-size SD cards, although their theoretical maximum capacity is the same. MicroSD cards have been surpassed by the faster microSDHC and microSDXC cards.

microSDHC: micro Secure Digital High Capacity. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. MicroSDHC is a physically smaller version of the SDHC card standard. It's designed for cellphones and other small devices. MicroSDHC cards are slower and usually have less capacity than full-size SDHC cards, although their theoretical maximum capacity is the same. MicroSDHC cards have been surpassed by the faster microSDXC cards.

microSDXC: micro Secure Digital eXtra Capacity. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. MicroSDXC is a physically smaller version of the SDXC card standard. It's designed for cellphones and other small devices. MicroSDXC cards are slower and usually have less capacity than full-size SDXC cards, although their theoretical maximum capacity is the same.

middleband: in computer terminology, an Internet connection that's faster than an ordinary analog telephone modem but slower than a broadband connection. An ISDN connection (up to 128Kbps per second) is considered middleband. Cable modems, DSL modems, and T1 lines all provide broadband speeds (about 1Mbps or faster). An analog modem (up to 56Kbps) is considered a narrowband connection. See broadband, cable modem, modem, narrowband.

mindshare: desirable public awareness or recognition. Example: "Yahoo has incredible mindshare among web surfers." Derived from "market share."

miner: someone who uses computers to create cryptocurrency (digital money). Also called a cryptominer.

Mini-ITX: an industry-standard motherboard (main circuit board) for personal computers. Measuring 6.7 x 6.7 inches, Mini-ITX motherboards are typically found in very small PCs. See ATX, Micro-ATX, motherboard, mainboard.

minicomputer: obsolete term for a computer that was smaller and less expensive than a mainframe computer, but larger and more expensive than a desktop computer. Whereas older mainframes often filled whole rooms, minicomputers were about the size of refrigerators. Minicomputers have been supplanted by smaller mainframes and especially by microprocessor-based servers. See mainframe, microcomputer, server, microprocessor, PC.

Mint: a popular version of the GNU/Linux operating system for computers. Created in 2006, it includes a graphical desktop and all of the system software and application software to make a complete ready-to-use system, also known as a "distribution" or distro. Mint is a derivative ("fork") of Ubuntu, another distro that itself is a fork of Debian. See also Linux, GNU, kernel, Unix.

MIS: management information systems. It's the department that installs and maintains computers at medium- to large-sized companies. Also known as the IT (information technology) department.

mispredict penalty: the penalty in wasted clock cycles that a microprocessor pays for wrongly guessing the outcome of a conditional branch. The processor must discard the results of any speculatively executed instructions and flush its pipelines of speculatively fetched instructions.

MITM: man in the middle. A method of intercepting secure communications by tapping into the computer network somewhere between the sender and the recipient. Often it works by presenting false credentials that impersonate one of those parties.

ML: (1) machine learning; (2) machine language. The first term is lately more common and describes computer programs that can "learn" by analyzing data and recognizing patterns. The second term is older and describes the lowest level of computer programming, sometimes called assembly language. Machine-language programmers write their code using the microprocessor's native instruction set instead of a higher-level abstract language. See AI, DL, GPT, neural network, assembler, assembly language.

MMA: mixed martial arts. An electronic game in which the player engages in simulated hand-to-hand combat. See FPS, MMO, MOBA.

MMO: massively multiplayer online game. An electronic game in which many players compete simultaneously over a local network or the Internet. See FPS, MMA, MOBA.

MMX: multimedia extensions, though Intel insists it's just a brand name. Introduced in early 1997, MMX consists of 57 new instructions that speed up multimedia tasks in x86-compatible microprocessors. It's also supported by chipmakers AMD, Transmeta, and VIA.

mo jo: mobile journalist. This slang term defines a modern journalist adept in multiple skills, such as writing (for print or web), still photography, and videography.

MOBA: multiplayer online battle arena. An electronic game in which two teams of players compete over a local network or the Internet. See FPS, MMA, MMO.

mobe: slang term for a mobile phone (cell phone).

mobo: slang term for a motherboard.

modem: modulator/demodulator. A device that allows computers to link over a telecommunications channel by converting digital data into electrical or radio signals and reconverting those signals back into digital data. Modems may operate over land lines (telephone wires or television cables) or wirelessly by radio. Modems operate at a variety of speeds, depending on the bandwidth of the telecommunications channel and their efficiency. See broadband, cable modem, middleband, narrowband.

Moore's law: a general principle, first expressed by engineer Gordon Moore, that the number of components integrated on affordable semiconductor chips increases at a relatively steady rate. When Moore initially described this principle in 1965, he predicted that component counts would double every 12 months. In 1975, he amended his prediction to a doubling every 24 months. Other people have split the difference to predict a doubling every 18 months. Moore's law isn't a true scientific law; it's an observation that traces the general progress of integrated circuits. Actual progress has fallen far short of Moore's predictions, but few people understand Moore's law, so it is widely misquoted and misinterpreted. See Epstein's amendment, Moron's law.

Moron's law: the number of ignorant references to Moore's law doubles every 12 months. Defined by Tom R. Halfhill in a Microprocessor Report article in 2004. See Moore's law, Epstein's amendment.

Morris Worm: a self-replicating program that infected and disabled thousands of computers on the Internet in November 1988. Named for its creator, Cornell University graduate student Robert Morris, it was the first "computer worm" to cause widespread network disruption. Morris wasn't malicious, however; he was experimenting with self-replicating code and didn't intend to cause harm. Nevertheless, he became the first person convicted of a felony under the Computer Fraud and Abuse Act of 1986. He atoned for his mishap and later became a professor at M.I.T. See worm.

motherboard: the main system board inside a computer. Usually, all the major components are attached to the motherboard, including the microprocessor chip, the core-logic system chipset, RAM chips, expansion slots, power supply, etc. Also known as a mainboard or mobo.

mouse: an input device for controlling an on-screen cursor. It's usually a separate peripheral with a roller ball and one or more buttons, but its functions may be carried out by a pressure-sensitive pad, a trackball, a light pen, or some other contrivance.

MP3: MPEG-2 Layer-3, a digital-audio standard that's part of the MPEG-2 audio/video standard. It defines a way to compress and decompress digital audio data to save memory, disk space, and bandwidth. Popular music is often stored in MP3 format for distribution over the Internet. See AAC, FLAC, codec, lossy.

MPEG: Moving Pictures Experts Group, an industry organization that devises standards for audio and video compression. Often mistaken as "Motion Pictures Experts Group."

MPEG-2, MPEG-3, MPEG-4: (also MPEG2, MPEG3, MPEG4) audio/video standards formulated by the Moving Pictures Expert Group and widely supported throughout the industry. They define methods for compressing and decompressing audio and video data to conserve resources in computers, digital TVs, and other multimedia devices.

MR: mixed reality. Synonymous with XR (extended reality), it describes glasses or goggles that can switch between AR (augmented reality) and VR (virtual reality). These devices may superimpose text or images on a real-world view or display a completely artificial view.

mSATA: Mini Serial Advanced Technology Attachment. A compact version of the SATA industry standard for attaching disk drives to computers. The mSATA version is for mobile computers, such as laptops, notebooks, and tablets. Bandwidth is the same as regular SATA. See ATA, Serial ATA, SATA.

MSB: most significant byte or bit. In a multibyte value, it's the byte that has greater value than the least significant byte (LSB). The position of the MSB depends on whether the architecture is little endian or big endian. Within a byte, the most significant bit is the leftmost bit.

multicore: two or more microprocessor cores on one chip. Until recently, almost all microprocessor chips contained a single processor core; designs with multiple cores are becoming commonplace. See core, microprocessor, manycore, massively parallel.

multidrop bus: a data-transfer interface that connects two or more devices. Technically, all buses are multidrop buses if they support more than two devices. A "bus" that supports only two devices is a point-to-point channel.

multiprocessing: running software on multiple computers, microprocessors, or processor cores. If the workload is divided evenly, it's symmetric multiprocessing; otherwise, it's asymmetric multiprocessing. See multicore, affinity.

multithreading: multiple threads of execution running through a program at the same time. For each thread, the computer carries out a different sequence of program instructions. For example, a word-processing program might use one thread to check the text for grammatical errors while using another thread to look for spelling errors. Also called concurrent execution or concurrency. See concurrency, thread, threadlock, deadlock.

munge: (pronounced "muhnj") to scramble or damage some data. Example: "When my computer crashed, it munged my spreadsheet."

MVP: minimum viable product. Slang term for a product in development that has just enough function to be minimally useful or worthy of further investment. It's often used to describe prototype products (including software) that the developers pitch to investors to attract funding.

********** N **********

n00b: see newbie.

NAN: neighborhood-area network. Usually a wireless Wi-Fi network for sharing Internet access among several households. See 802.11, LAN, WAN, Wi-Fi, WLAN.

narrowband: in computer terminology, an Internet connection that's slower than middleband or broadband connections. An analog modem (up to 56Kbps) is considered a narrowband connection. An ISDN connection (up to 128Kbps) is considered middleband. Cable modems, DSL modems, and T1 lines all provide broadband speeds (about 1Mbps or faster). See broadband, cable modem, middleband, modem.

NAS: network-attached storage. A stand-alone mass-storage device (disk drive, tape drive, or CD-ROM jukebox) attached to a computer network without being part of a server. NAS can be more economical and reliable than file servers for network storage and backups. See SAN.

native code: program code written to run on a specific platform. Nonnative code may be able to run on the same platform with help from an emulator. See code, emulator, object code, source code.

native platform: the combination of an operating system and a microprocessor architecture that determines what kind of software can run on a particular computer. An example of a platform is Windows XP on an Intel x86-compatible processor. The Macintosh is a different platform because it runs Mac OS on a PowerPC processor. Each is a native platform to itself but is nonnative to other platforms.

NDA: nondisclosure agreement. A contract in which the signer promises not to divulge certain information about a company, product, or service. Companies often require journalists, analysts, and business partners to sign NDAs before disclosing advance information about something the company is working on. Usually, NDAs expire on the date of the public announcement.

nerd: someone who is technically adept but socially inept. Synonym: geek.

net neutrality (network neutrality): enforcing equal delivery priority for all data packets traversing the Internet, regardless of the nature of the packets or the effect on network traffic. Under this policy, government regulations would require Internet routers to always deliver packets in the order in which the routers receive them, no matter what the contents, sources, or destinations of the packets. Example: earlier-arriving packets carrying e-mail would get higher priority than later-arriving packets carrying live audio/video streams or online gaming traffic, even if this priority degrades the audio/video or gaming experience. Likewise, government regulations would prohibit Internet providers from charging their customers higher rates for higher-priority delivery. The alternative to net neutrality is traffic shaping or traffic management, which allows Internet providers to optimize network traffic by handling packets differently. See Internet, network, packet, packet switching, traffic shaping.

netizen: network citizen. Someone who participates in virtual communities on the Internet. The original meaning implied that everyone who uses the Internet shares some common interests, such as concern for online privacy and open access to information—a concept now largely discredited.

network: two or more computers linked together for mutual communication. The link can be wired or wireless. See Ethernet, LAN, NIC.

neural network, neural net: a crude computer simulation of the human brain's synapses and pathways. Because it's not a true brain simulation, sometimes it's called an artificial neural network (ANN). Neural nets are commonly used in machine-learning and artificial-intelligence programs. There are variations, including a convolutional neural network (CNN), deconvolutional neural network (DNN), deep neural network (also DNN), and spiking neural network (SNN). See AI, ML.

newbie: a new, usually clueless, user. Often derogatory, but not always. (Variations: newb, n00b.)

newsgroup: an online "bulletin board" where people can post and read text messages, organized by topic. There are thousands of topical newsgroups. They operate on Internet servers and are one of the oldest applications of the Internet, predating the web. In the 1990s, newsgroups largely supplanted the similar bulletin-board systems operated on individual computers, which were accessed directly by dial-up connections instead of on the Internet. In the 2000s, newsgroups were largely supplanted by blogs and social networks. See Internet, BBS, blog, social network, World Wide Web, Web 2.0.

NFT: non-fungible token. An encrypted digital code that verifies exclusive ownership of some specific digital property. It's like the deed or title to a house or car, except both the document and the property exist only in digital form. The property can be a song, video, visual artwork, or anything else stored in a digital format. Buyers can purchase NFTs using conventional money or a digital currency such as Bitcoin.

NIC: network interface card (pronounced "nick"). An expansion card that plugs into a motherboard slot and allows connection to a network. See Ethernet, interface, LAN, motherboard, network.

NIH: "not invented here." An attitude biased against ideas, products, or technologies from an outside source. Example: "Even though it's better, our engineers won't use that technology because it's NIH."

node: (1) a client device attached to a computer network, or (2) a generation of chip-fabrication technology. In the latter usage, "node+1" means the next-generation technology, and "node–1" means the previous generation.

nomophobia: the fear of being without a mobile phone ("No Mo-bile").

nonvolatile: see volatile.

n00b: see newbie.

north bridge: the part of a PC system chipset that connects directly to the microprocessor on the system I/O or frontside bus. The north bridge may have interfaces that connect to main memory (RAM), the AGP graphics channel, PCI bus, and south-bridge part of the system chipset. The north bridge may also connect to the microprocessor's Level 2 cache if the processor doesn't have a separate backside bus or integrated on-chip L2 cache.

NSFW: not safe for work. A web page or email message that contains content (such as porn) that may get an employee in trouble if viewed at a workplace.

NUMA: nonuniform memory access or nonuniform memory architecture. It describes a multiprocessing system in which the processors can access nearby memory more quickly than they can access more-distant memory. NUMA is unavoidable in large multiprocessing systems. See multiprocessing, memory.

NVDIMM: Nonvolatile dual inline memory module. A plug-in memory stick or card containing nonvolatile solid-state memory instead of conventional DRAM memory. Unlike DRAM, nonvolatile memory retains data even when powered off. Examples are flash memory and 3D XPoint memory. Intel and Micron plan to introduce NVDIMMs using 3D XPoint memory in 2017. Although not quite as fast as DRAM DIMMs, NVDIMMs will be nonvolatile and much faster than flash memory. See DRAM, DIMM, volatile, 3D XPoint.

NVM: nonvolatile memory. Solid-state memory that retains data even when powered off. Examples are flash memory and 3D XPoint memory. See 3D XPoint, flash memory, volatile.

NVMe: Nonvolatile Memory Express. An interface for attaching solid-state storage drives to computers and other devices. Introduced in 2011, NVMe is designed specifically for SSDs (solid-state drives) built with flash memory, 3D XPoint memory, or other types of nonvolatile memory. It's faster than previous interfaces designed for spinning-metal hard disk drives (HDDs), such as Serial ATA (SATA) or Serial-Attached SCSI (SAS). See NVM, flash memory, 3D XPoint, SSD, SATA, SAS.

nybble: half a byte, or four bits. Also spelled "nibble." Programmers sometimes manipulate these small quantities, though not often these days. See byte and bit.

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object: a structure in an object-oriented program that consists of variables and methods. Analogous to a subroutine in procedural languages.

object code: the actual program code a computer executes. Programmers write in source code, which a compiler converts into object code (also called executable code, binary code, or machine code). Object code is specific to a particular microprocessor architecture, so a program compiled for an x86 processor won't run on a PowerPC processor or vice versa.

OC-1, OC-3, OC-12, OC-48, OC-192: Optical Carrier transmission standards for fiber-optic networks. See SONET.

OCR: optical character recognition, the process of converting the digitized image of text into editable text. OCR software usually starts with a digitized image of text captured by a scanner, then analyzes the image to identify individual characters, and finally converts those characters into their ASCII equivalents.

octal: a base-8 number system used in computer programming. There are eight digits, 0 through 7. Octal 10 equals decimal 8. Programmers use octal numbers to represent binary numbers in a more compact form. Hexadecimal is more popular than octal for this purpose.

ODF: Open Document Format. A proposed standard for defining the file formats of electronic documents, such as those created by word processors and spreadsheets. ODF allows different programs on any computers to easily share documents. ODF is based on XML and is supported by the Open Office software suite. Not to be confused with Microsoft's rival format, OOXML, implemented in Microsoft Office 2007. See OOXML, XML.

OEM: original equipment manufacturer. A manufacturer that sells equipment to another company, which in turn resells the equipment after repackaging or rebranding it.

OLPC: One Laptop Per Child. A nonprofit project sponsored by the faculty of the Massachusetts Institute of Technology (MIT) Media Lab. OLPC's goal is to manufacture sturdy laptop computers that can sell for about $100 in emerging markets for use by schoolchildren. The vision is to spread education and Internet access throughout the world.

OOO: out of order (sometimes written O-O-O). To increase performance, some microprocessors can execute program instructions out of their original order in the instruction stream before retiring the results in order. See out-of-order execution.

OOP: object-oriented programming. OOP is not a programming language, but rather an approach to designing languages and programs. Object-oriented programs consist of independent modules that interact with each other in carefully defined ways. OOP is intended to speed development and improve reliability by encouraging code reuse.

OOXML: Office Open eXtensible Markup Language. A standard way of defining electronic documents, such as those created by word processors and spreadsheets, that allows different programs to share the documents while preserving the formatting. Microsoft created OOXML by extending XML. The Microsoft Office 2007 software suite supports OOXML. Not to be confused with Open Document Format (ODF), a rival formatting standard proposed by other companies and supported in the Open Office software suite. See ODF, XML.

open source: software whose source code is freely distributable and cannot be copyrighted or owned by anyone. See source code.

operand: a numeric value or register address used by a program instruction. For example, an instruction that adds 2 + 3 might have two immediate operands (2 and 3) or the addresses of two registers that hold those values; those are input operands. A third operand might be the address of a register in which the CPU stores the result, sometimes called the output operand.

operating system: the main program on a computer that manages system resources so other programs can run. Windows, Linux, Unix, Mac OS, iOS, Android, and MS-DOS are examples of operating systems. The OS handles low-level tasks, such as memory management, peripheral I/O, and interrupt processing. See kernel, Windows.

opt-in: to sign up for something, such as an e-mail list; the opposite of opt-out.

opt-out: to decline an offer; the opposite of opt-in.

OS/2 Warp: an IBM operating system, now defunct. It ran on x86-compatible microprocessors in PCs and servers. IBM and Microsoft announced OS/2 in 1987 and worked together on it, but later they split and Microsoft created Windows NT (now Windows XP) instead.

Osborne 1: a landmark personal computer introduced by Osborne Computer in 1981. It was the first popular transportable computer; "transportable" means it was designed to be carried from place to place, but it didn't run on batteries. Although quite heavy (24 pounds) and the size of a suitcase, the Osborne 1 had a built-in video screen (5 inches, monochrome), twin 5.25-inch floppy disk drives, a hard case, and a carrying handle, so it was self-contained. It also had a 4MHz Zilog Z80 microprocessor and 64KB of RAM, and it came with the CP/M operating system and some business software. It was designed by Adam Osborne (1939–2003) and Lee Felsenstein. Later, the Osborne 1 was superseded by transportable IBM-compatible PCs and laptop computers. See Osborne effect.

Osborne effect: when the announcement of an upcoming product kills sales of the product it will replace. Named for Adam Osborne, charismatic founder of Osborne Computer, who inadvertently stalled sales of his Osborne 1 by preannouncing two new models in 1983. See Osborne 1.

OTA: over the air. Usually, this term describes remote software updates for computing devices deployed in the field. The device may download the updates through a wired or wireless (literally, over-the-air) network. See Internet of Things (IoT).

out-of-order execution: the ability of a microprocessor to rearrange the order of program instructions and execute them out of order while the program runs. It's a technique for using the processor's internal resources more efficiently. However, the processor always saves the instruction results in their original program order. Abbreviated OOO or O-O-O.

overclocking: boosting a microprocessor's performance by raising its clock frequency beyond the nominal rating. Normally it's done by changing jumper settings on the motherboard or by changing BIOS settings. Overclocking may lower reliability.

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P2P: peer to peer. (1) A network that allows clients (the peers) to communicate directly with each other without going through a central server; (2) a method of sharing files over the Internet that works directly from one client to another without storing the files on a server. MP3 music-sharing applications are examples of P2P.

P6: Intel's code name for a sixth-generation x86 microprocessor chip. The Pentium Pro was the first P6-series processor, followed by the Pentium II, Celeron, Xeon, and Pentium III.

packet: a bundle of data that travels over a network from one computer to another. The sending computer divides the data to be transmitted into packets rather than sending the data as a continuous stream; if something interferes with the transmission, only the dropped packets have to be sent again. Each packet has a header that identifies its position in the sequence and its destination. Packets also carry information that helps the receiving computer detect and correct some transmission errors.

packet storm: a network problem caused by a faulty device that won't stop broadcasting useless data over the network. (Packets are bundles of data.) Packet storms can slow down or paralyze network traffic until someone shuts off the faulty device and corrects the problem. Sometimes a malicious hacker tries to paralyze a computer server or network by deliberately aiming a packet storm at it—a crime known as a denial-of-service attack. See DoS, DDoS.

packet switching: a method of sending data over a network in packets or bundles of data instead of transmitting the data as a continuous stream. Different packets may arrive at their destination by different routes; each packet has a header that identifies its position in the sequence so the receiving computer can reassemble the packets in their original order.

page miss: when a microprocessor can't find the instructions or data it needs in any of its caches or main memory. As a last resort, it looks in the operating system's swap file or in a DLL on the hard disk. This wastes millions of processor cycles. See cache, DLL.

PAN: personal-area network. A computer network that operates on a single person, or within the immediate vicinity of a person or a small group of people. Usually it is wireless, using something like Bluetooth technology to link two or more devices so they can exchange data. IBM has demonstrated a PAN that can pass data between two people who touch hands.

paradigm shift: a radical change that upsets the status quo and forces adaptation. It rarely happens as often as claimed or as quickly as predicted. See disruptive technology.

parallel interface: a connection between two electronic devices (usually a computer and a peripheral, such as a printer or disk drive) that carries data on numerous wires running side by side. Examples of parallel interfaces include IDE (ATA), SCSI, and the Centronics printer interface (IEEE-1284). Antonym: serial interface.

parallelism: the ability to perform multiple tasks at the same time. Parallelism speeds up processing, but some tasks rely on the result of another task, so they must be executed serially. See embarrassingly parallel.

parameter: In programming, a value passed from one program to another, from one part of a program to another part of the same program, or from a program to an operating system. The parameter may be a number, a text string, or some other value that passes information to the receiver. Parameters are often required when calling an API.

PARC: Palo Alto Research Center. Xerox established this fertile laboratory in Palo Alto, California in the 1970s. It was the birthplace or proving ground of many important technologies, including the laser printer, Ethernet, the graphical user interface (GUI), desktop publishing, and to some degree, the personal computer. It was on a tour of PARC in the early 1980s that Apple co-founder Steve Jobs was inspired to bring the GUI to the Lisa and Macintosh computers. Unfortunately, stodgy executive management and internal politics kept Xerox from taking commercial advantage of all these innovations.

Pascal: a programming language devised in the 1970s for teaching structured programming. It was a reaction against earlier languages such as BASIC that were loosely structured. Although Pascal became a powerful language for professional software development, it has lost popularity.

passkey: a safer alternative to log-in passwords, invented by a computer-industry consortium called the FIDO Alliance. If adopted, passkeys will use several security methods to authenticate a user's identity when logging into a device, website, or service. See FIDO Alliance.

patch: a modification to a software program, usually to fix a bug, and usually distributed after the program is already in the hands of users.

paywall: a password screen on a website that blocks entry to visitors who haven't paid to access content on the site. Paywalls are typically used by publications and porn sites.

PC: personal computer. Usually it refers to Windows-compatible computers, but it's also used generically to refer to all personal computers, including Macintoshes. The first IBM PC that led to today's Windows-compatible PCs appeared in 1981. However, ready-to-run personal computers from other companies became available in 1977 and kit-built personal computers date to around 1975.

PC Card: a PCMCIA expansion-card standard for memory cards and peripherals that is particularly popular on mobile computers. See PCMCIA, ExpressCard.

PCB: printed circuit board. A computer motherboard is an example of a PCB.

PCI: Peripheral Component Interface, an industry standard for attaching peripheral devices to PCs. It was introduced by Intel in 1992. Most PC motherboards have three or more PCI expansion slots. The basic PCI standard has a 32-bit-wide bus that runs at 33.3MHz, yielding 133MB per second of maximum bandwidth. Higher-performance versions of PCI may have a 64-bit bus and/or run at 66.6MHz, yielding up to 533MB per second. It has been supplanted by PCI Express.

PCI Express: a peripheral interface created by Intel and introduced in 2003. PCIe was formerly known as 3GIO (Third-Generation Input/Output). Unlike its predecessors, PCI and PCI-X, PCIe uses serial instead of parallel connections, although multiple serial lanes can work together for greater throughput. The initial PCIe 1.0 speed was 250MB/sec per lane in each direction, almost twice as fast as classic 32-bit/33.3MHz PCI. Speeds increased to 500MB/sec in v2.0 and to 985MB/sec in v3.0. The newest v4.0 standard provides 1,969MB/sec.

PCIe: see PCI Express.

PCMCIA: (1) Personal Computer Memory Card International Association; (2) "people can't memorize computer industry acronyms." Term 1 usually refers to a compact expansion-slot standard created by the PCMCIA; it's also known as a PC Card slot. Term 2 is a popular definition that makes fun of technical abbreviations. See PC Card, ExpressCard.

peer-to-peer networking: a simple way of connecting multiple computers or other devices together without a central server or hub. Each computer or device on the network is "equal" or a peer to every other computer or device. It's a convenient way to share files, printers, and other resources. Abbreviated P2P.

pen tester: someone who penetrates computers and networks to test their security. Pen testing usually aims to strengthen security, not to exploit vulnerabilities. Pen testers are also known as white-hat hackers.

peripheral: an accessory device that plugs into a computer. Printers, modems, disk drives, scanners, keyboards, and mice are peripherals.

permatemp: a temporary contract worker who stays on the job so long that it's tantamount to regular employment, except without all the fringe benefits. In a landmark class-action lawsuit, Microsoft was successfully sued by permatemps who demanded better treatment.

PET: Personal Electronic Transactor. This rather contrived acronym, rarely spelled out, was the brand name of a series of personal computers first introduced by Commodore in 1977. The original Commodore PET was among the first three personal computers introduced that year that were available off the shelf and didn't require assembly. Together with the Apple II and TRS-80 Model 1, the PET helped move computing beyond the electronics-hobbyist era toward mass popularity. See Apple II, TRS-80.

petabit: 1,024 terabits, or 2^50 bits. Abbreviated Pb. See bit, byte.

petabyte: 1,024 terabytes, or 2^50 bytes. Abbreviated P, PB, or pB. See bit, byte.

petaflops: 1,000 trillion floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called PFLOPS. See FLOPS, floating point, FPU.

PETG: polyethylene terephthalate glycol is a type of plastic filament that feeds a 3D printer.

PFLOPS: 1,000 trillion floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called petaflops. See FLOPS, floating point, FPU.

phablet: (phone + tablet). Slang term for a smartphone large enough to be a small tablet.

phishing: the malicious use of emails, text messages, or web pages that seem legitimate but that try to fool users into divulging private information. A typical example is an email message claiming to be from eBay that leads the victim to a fake eBay web page requesting the user's eBay username, password, and credit card number. See spear phishing, vishing.

phubbing: ignoring someone while using a smartphone (phubbing = phone + snubbing).

PHY: physical-layer chip. A chip (or part of a chip) that implements the interface to a peripheral device or another chip.

pi: (1) a transcendental number (3.141592653...) describing the ratio of a circle's circumference to its diameter, or (2) part of the brand name of inexpensive single-board computers. See Raspberry Pi.

Pi-Hole: software that automatically removes online advertisements from incoming Internet traffic on a home or office network. Pi-Hole is open-source software for the Linux operating system. Although virtually any computer can host Pi-Hole, it's overkill to dedicate a PC, so typically the software runs on a Raspberry Pi microcomputer costing as little as $10. The software acts as a domain-name server (DNS) sinkhole for the local network and can strip the ads from any networked devices, including PCs, tablets, smart TVs, and phones. Users can define exceptions in a whitelist if they want ads from certain vendors. See DNS, Linux, Raspberry Pi, open source, whitelist.

picocell: see base station.

PIM: personal information manager. A program or device that keeps track of appointments and schedules.

PIN: personal identification number—a password.

ping: (1) (noun or verb) a program that sends a short packet to a network address to see if a computer or device at that address is present and responding; (2) slang for any query intended to elicit a response from a machine or person. Example: "Is Jerry back from his business trip yet? Ping him to find out."

pipeline: a microprocessor's "assembly line" for executing program instructions. A pipelined function unit in a processor separates the execution of an instruction into multiple stages. Instructions flow through the pipeline like cars on a factory assembly line; at any moment, multiple instructions are in various states of completion.

pixel: a dot on a video screen. Everything on the screen is formed of pixels. More pixels are better, because the screen can display more detailed images. Screen resolution is often expressed in pixels—1024 x 768 means a screen displays 1024 pixels horizontally by 768 pixels vertically, for a total of 786,432 pixels.

pixel peeping: critically examining digital images at 100% magnification on a video screen. Pixel peeping can reveal lens aberrations, digital noise, and other image flaws normally visible only in very large prints. For some pixel peepers, it becomes an obsession, driving them to buy increasingly expensive cameras and lenses. (Variations: pixel-peeping, pixel-peeper, pixelpeeping, pixelpeeper.)

pixelated: the blocky look of a digital image whose individual pixels are clearly visible. Usually undesirable, pixelation occurs when a digital image is enlarged beyond the limit of its pixel resolution. See pixel, staircasing.

PLA: polylactic acid is a type of plant-based plastic filament that feeds a 3D printer.

platform: the combination of an operating system and a microprocessor architecture that determines what kind of software can run on a computer. An example of a platform is Windows XP on an Intel x86-compatible processor. The Macintosh is a different platform because it runs Mac OS on a PowerPC processor.

plug-in: a program that attaches itself to another program to add functionality. Usually the host program must be designed to accept plug-ins. If the plug-in API is public, any programmer can write a plug-in. An example of a host program is Adobe Photoshop. An example of a Photoshop plug-in is a conversion program that opens the RAW files of a specific model of digital camera. See API, RAW.

plugfest: an organized event at which engineers gather to test something, usually a new technical standard with which they must comply.

podcast: a digitized audio file, often in the format of a talk-radio program, made available for downloading or streaming over the Internet. Podcasts are usually recorded by enthusiasts of a particular topic—such as sports, politics, or popular culture—who lack access to a conventional radio station. Instead, podcasters record their program as a digital file and post it on a website. Listeners can download and listen to the recording on a computer, smartphone, or portable music player. If the podcasting website supports RSS, listeners can automatically receive new programs. See RSS, podfaster.

podcaster: someone who records and distributes podcasts.

podfaster: someone who saves time by listening to a podcast at faster than normal speed. The playback software can increase the audio speed without raising the pitch and can shorten pauses between words and sentences. Studies indicate that comprehension declines sharply when podfasting exceeds twice the normal speed. See podcast, podcaster.

polygon: A 2D figure (usually a triangle or rectangle) that's the building block of a 3D screen object. It usually takes hundreds or thousands of polygons to form the skeleton of a 3D object.

PoP: package-on-package. A space-saving technique that stacks one chip atop another, with short wires connecting their pins. Usually, one chip is memory and the other is a microprocessor. Often used in cell phones and other small devices.

POP3: Post Office Protocol 3, an Internet standard that defines how computers can retrieve e-mail stored on mail servers. POP3 is a popular worldwide standard supported by most mail clients, including Microsoft Outlook, Netscape Messenger, and Eudora. Another standard is IMAP.

port: a connector for transferring data into or out of a computer or peripheral. Most ports allow two-way transfers, but some older ports (such as parallel printer ports and PS/2-standard keyboard/mouse ports) support one-way transfers only. Internally, a port connects to a bus or datapath. There are many different physical and electrical characteristics and transfer protocols for ports, so different ports aren't compatible. See bus, datapath, I/O, protocol.

POST: power-on self-test. Computers and peripherals often have a small program that checks for problems when the power is switched on. The POST program is usually stored in ROM or flash memory. Also known as BIST (built-in self-test).

PowerNow: a power-saving feature in some AMD microprocessors designed for notebook computers (such as the K6-2+, K6-III+, and Athlon 4). It works by automatically reducing the chip's supply voltage and clock frequency when the demand for processing power is low. It automatically raises the voltage and frequency when the demand for performance is higher. See LongHaul, LongRun, SpeedStep.

PPA: power, performance, area—the criteria for evaluating chip technology. Ideally, a chip's power is low, its performance (throughput) is high, and its area is small. Each new generation (node) of chip-fabrication technology strives to improve those measures.

PPGA: plastic pin grid array, a type of packaging for microprocessors that distributes the pins in a grid over the entire bottom of the chip instead of around the periphery. Intel uses PPGA packaging for some Pentium III and Celeron processors that fit Socket 370. Other versions of those processors use FCPGA packaging, also compatible with Socket 370.

prefetching: when a microprocessor loads program instructions or data from main memory (RAM) in advance of execution. Typically, the processor prefetches the instructions into the instruction cache or the data into the data cache. When the processor needs the instructions or data, it retrieves them directly from the cache, which is faster than retrieving them from main memory because cache memory (SRAM) is much faster. See cache.

print server: a shared computer that provides printer services to client computers on a network. Print servers typically have one or more fast laser printers. They are often a more economical and efficient solution that equipping every desktop PC with a printer.

procedural language: a computer-programming language that doesn't enforce or encourage the grouping of related subroutines into independent code modules. It's the opposite of object-oriented programming (OOP). Programs written in procedural languages tend to be monolithic, while OOP encourages the division of a program into modules that are reusable in future programs. However, the latest versions of procedural languages such as C, BASIC, and Pascal have adopted some concepts of OOP. See function, method, procedure, OOP.

procedure: a subroutine in a computer program that generally does not return a value when called. A procedure named SaveFile might save a file on disk, then return control to the calling program or routine without returning a value. See function, method.

process technology: a manufacturing process for chips. Chips have layers of semiconductors, insulators, and conducting interconnects; a particular process technology determines what kinds of chips can be fabricated. Process technologies are usually described by the minimum size of the semiconductor elements: 0.25 micron, 0.18 micron, etc. Smaller is better, because the transistors can be packed more densely and the chip can run at a lower voltage and higher clock speed while consuming less power.

processor: see microprocessor.

program: a list of instructions for a computer. Most instructions are executed by the CPU (microprocessor).

protocol: a formally defined way to perform an action. Diplomatic protocols specify how to greet foreign dignitaries; computer protocols specify interactions between computing devices and programs. For example, HTTP (hypertext transfer protocol) defines how web servers and browsers should exchange data over the Internet.

proxy server: a server (networked computer) that controls the network access of other computers on the network. Usually, businesses use proxy servers to filter Internet traffic to and from PCs on the company's internal local-area network (LAN). Proxy servers provide security and also conserve Internet Protocol (IP) addresses. An enterprise may have a relatively small number of IP addresses shared among a larger number of PCs; the proxy server routes Internet traffic to the appropriate PC. See network, LAN, server, IP, IP address.

PS/2 port: a connector on IBM-compatible PCs typically used for a keyboard or mouse. It was introduced on IBM PS/2 computers in the late 1980s to replace the older PC/AT keyboard connector. In the future, PS/2 ports will probably be superseded by USB ports.

public-key cryptography: a software method that protects data by using encryption and digital "keys" for unlocking the data. It commonly protects sensitive communications (such as email) and secure log-ins to websites. Each participant must create a public key and a private key. The public key encrypts the data and can be freely shared. The private key, which must be kept secret, decrypts the data. The most popular public-key system is RSA. See RSA, passkey, FIDO Alliance.

PUF: physical unclonable function. A unique identifier embedded in a microprocessor or other integrated circuit. To derive a unique identifier for each otherwise identical chip, the PUF typically uses some physical characteristic that randomly varies slightly as a result of normal manufacturing processes. The PUF is used to create a unique identifier for security purposes and is often described as a digital fingerprint.

pwn, pwned: to compromise the security of someone else's computer, or to fool someone into disclosing secure information. This term has additional meanings, not all of them malicious, especially among gamers. Origin is disputed. Some say it's derived from owned, as in "I own you." Others say it's derived from pawned, a term sometimes used in chess. It may be pronounced to rhyme with "own" or with "pawn."

pundits: experts who frequently offer (presumably knowledgeable) opinions on their special subjects. Many pundits are analysts who make a full-time living by studying, writing, and talking about a specific subject.

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QA: quality assurance. The process of testing hardware or software for bugs that need fixing. Also known as quality control.

QC: (1) quality control or (2) quantum computing. Quality control is the process of testing hardware or software for bugs that need fixing; also known as quality assurance. Quantum computing is a major departure from conventional digital computing (also known as classical computing). Instead of using digital electronics to calculate numbers in binary format, QC employs atomic-level quantum behavior to perform many simultaneous calculations. The basic element is a quantum bit or qubit. QC is still experimental but has the potential to vastly outperform classical computers, at least for some types of calculations.

Qi: (pronounced "chee") is a proposed industry standard for wirelessly recharging batteries in consumer electronics. Its backer is the Wireless Power Consortium (WPC).

QoS: quality of service. Usually it describes network switching or routing that assigns different levels of priority to different data packets, depending on their source, destination, or contents. For example, a business might pay higher network-access fees to ensure that its packets get higher priority than those carrying gossip from a teenage chat room on AOL.

QPI: see QuickPath Interconnect.

quadrilateral texturing: a method of applying lifelike surfaces to 3D objects rendered in computer graphics. See textures, texture mapping.

quantum computing: a new technology that departs significantly from conventional digital computing (also known as classical computing). Instead of using digital electronics to calculate numbers in binary format, QC employs the quantum behavior of atoms to perform many simultaneous calculations. The basic element is a quantum bit or qubit. QC is still experimental but has the potential to vastly outperform classical computers, at least for some types of calculations.

qubit: a quantum bit, the basic element of quantum computing. In a major departure from conventional digital computing that represents numbers as binary digits or bits, a qubit can represent multiple numbers simultaneously by exploiting the quantum behavior of atoms. A quantum computer can potentially outperform a conventional computer, at least for some types of calculations.

query engine: a program that allows users to retrieve specific information from a database. Usually it supports structured queries using Boolean logic. See database, database engine, Boolean logic, SQL.

QuickPath Interconnect (QPI): Intel's answer to HyperTransport—a high-speed point-to-point serial connection between multiple processors or between a processor and a memory controller. Formerly known as CSI (Common System Interface). QuickPath first appeared in 2008 and replaces the front-side bus on some Intel processors. See CSI, frontside bus, HyperTransport, microprocessor.

QWERTY: the most common keyboard layout. Named for the first six keys in the top row of letters, it was created in the 19th Century for manual typewriters. It's deliberately inefficient to prevent a typewriter's mechanical strikers from colliding during rapid typing. A more efficient layout is named Dvorak after its inventor but is much less popular.

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R&D: research and development. R&D is a company's investment in better technology and new products.

RAID: redundant array of inexpensive disks. RAIDs are multiple hard disk drives usually found in servers. They protect important information by redundantly storing it on multiple drives, so the failure of a single drive won't lose any data.

RAM: random-access memory. RAM is the most common type of memory found in computers. Main memory is DRAM and caches are SRAM, both forms of RAM. All RAM is volatile.

Rambus: a company that designs and licenses memory interfaces based on its proprietary RDRAM and DRDRAM specifications. These interfaces are very fast and have narrower buses than standard memory interfaces.

ransomware: malicious software that secretly encrypts data on a victim's computer or network and then demands a ransom to unlock it. To avoid detection, the attacker usually operates remotely over the Internet and demands payment in a cryptocurrency such as bitcoin. Victims have included hospitals, police departments, and local governments as well as individuals. The ploy assumes the victim lacks an offline backup of the encrypted data. Also known as cryptojacking.

RAS: row address strobe. A signal that together with the CAS locates a memory address in a RAM chip. See CAS, RAM, DRAM, CL1.

Raspberry Pi: brand name for a series of inexpensive single-board computers designed mainly for hardware hobbyists. Created by a United Kingdom nonprofit (Pi Foundation), the first model debuted in 2012. Later models are more powerful and capable, although a very low-cost version serves smaller projects. Typically they are sold as caseless boards, although the Pi 400 is packaged in a compact QWERTY keyboard. Other companies offer many accessories, including cases, peripherals, development tools, and software. All Pi boards use 32- or 64-bit ARM processors and run a special version of the GNU/Linux operating system or (less commonly) the ARM version of Microsoft Windows 10. The high-end Pi is usable as a personal computer. Robotics are a common application. See GNU, Linux, QWERTY, Windows.

RAW: a file format for digital photographs consisting of raw data from a digital camera's image sensor. "RAW" is not an acronym, but is often capitalized like an acronym for consistency with other file formats (JPEG, TIFF, etc.). RAW files usually preserve more bits of color depth than other formats and therefore allow greater manipulation in image editors. RAW files are usually specific to a camera model and require special software to open.

RCE: remote code execution. The ability to run a program on another computer attached to the same network or over the Internet. RCE can be used for legitimate purposes but is often exploited by malicious hackers who penetrate vulnerable computers.

RDRAM: Rambus dynamic random-access memory. A proprietary but widely licensed memory standard controlled by Rambus. RDRAM usually offers higher performance than other types of DRAM.

read/write head: the electromagnetic component in a disk drive or tape drive that reads and records data on a magnetic surface.

reality distortion field: a mythical "field" said to surround the late Steve Jobs, Apple's cofounder and CEO. Jobs was so mesmerizing at public product introductions, and so aggressive when asserting his viewpoints in private meetings, that Apple employees coined this term to describe how reality seemed to warp in his presence. A weird side effect of the distortion field is that the term itself is simultaneously derogatory and complimentary.

reality media: pretentious term for blogs attempting to compete with traditional print and broadcast media. See blog, blogosphere, weblog.

register: a small storage cell in a microprocessor that temporarily holds values needed by a running program. Usually the general-purpose registers are 16, 32, or 64 bits wide. Program instructions put values in the registers, perform operations on the values, and copy the results back to memory.

register file: see register set.

register set: the registers common to a particular microprocessor architecture; one of the distinguishing factors of an architecture. See architecture, microprocessor, register.

release candidate: programmer's term for a version of software that may be ready for shipment as a product. If the release candidate passes final testing, it becomes the gold master. See alpha, beta, gold master.

render farm: a collection of powerful computers for rendering 3D graphics too complex to be drawn in real time. Movie studios use render farms to generate professional-quality animation for output to film. The networked computers often run day and night to create a few frames of high-quality graphics.

resolution: an expression of detail in an image or the accuracy of a representation. In digital imaging, resolution refers to the number of pixels in an image or a portion of the image; the more pixels, the higher the resolution, and the greater the detail. Resolution also describes the accuracy of a representation, such as the fidelity of digitally sampled sound or radio signals; again, higher resolution means higher quality.

retrocomputing: running software emulators of old computers on today's computers. See emulator.

return-oriented programming: see gadget.

rev: techie slang for "revise" or "revision." Examples: "We're going to rev our software to fix the bugs" and "We'll fix those bugs in the next rev."

revenge porn: the unsavory practice of distributing lewd photos or videos of a former lover. The jilted partner may post the images on a website or attach them to emails sent to the victim's friends, family, or coworkers.

reverse engineering: the process of creating something by analyzing somebody else's finished example. Engineers using this technique might examine a competitor's product to see how it works and then design a similar product. See clone.

RFID: radio-frequency identification. Usually refers to a tiny chip that responds to a specific radio-frequency query by broadcasting some preprogrammed data within a very limited range. Often the RFID chip is implanted in a product or container for identification and tracking purposes. The chip is so small that it derives its power from the incoming radio signal.

Rickroll: an Internet prank in which a hyperlink leads not to the indicated web page but instead to an audio clip of Rick Astley's 1987 hit song "Never Gonna Give You Up." Rickrolling or Rick-rolling started around 2007.

RISC: reduced instruction-set computing. RISC is an architectural design style for microprocessors that was invented to supersede CISC. It strives to improve performance by encoding program instructions in a fixed-length format and by using simpler instructions that execute in fewer clock cycles. RISC also performs arithmetic and logical operations on operands in registers instead of in memory. Examples of RISC architectures include ARM, MIPS, ARC, PowerPC, SPARC, Alpha, and PA-RISC. See microprocessor, architecture, CISC, x86.

RISC-V: an open-source microprocessor architecture. This freely licensed instruction-set architecture (ISA) was created in 2010 at the University of California at Berkeley by graduate students Yunsup Lee and Andrew Waterman and their professors Krste Asanovic and David Patterson. They began promoting it widely in 2014. Major companies such as Alibaba, Nvidia, NXP, Qualcomm, and Western Digital have designed RISC-V processors. See microprocessor, ISA, RISC.

road warrior: a business traveler who works while on the road, especially by using a mobile computer and/or mobile communication device. A typical example of how modern businesspeople use military and sports terminology to dramatize paper-pushing. See windshield warrior.

robopocalypse: (robot + apocalypse) a hypothetical future event in which artificially intelligent machines seize control of the world, enslaving or exterminating humans. See artificial intelligence, singularity, Turing test, foom.

ROFL: "rolling on the floor laughing." A brief response to a humorous e-mail message or online posting. See LOL.

ROM: read-only memory. Computer memory that permanently retains data, which can't be erased or changed even if electrical power shuts off. The data is imprinted during manufacturing. For example, a videogame cartridge typically stores the game program in ROM.

RoT: root of trust. A trusted security module in a computer or other electronic device. The RoT typically verifies that the computer's startup or boot software hasn't been corrupted or altered by a malicious hacker.

ROT13, ROT 13: a simple cipher in which the characters in a message are alphabetically shifted 13 positions to the right. Shifts beyond "Z" wrap around to the beginning of the alphabet. For example, "cat" becomes "png". In the early days of the Internet, users often encoded publicly posted messages in ROT 13 if the text was deemed too offensive.

router: a highly specialized computer for networking. Routers receive the packets of data that travel over networks (such as e-mail messages and web pages) and forward them toward their destinations. All Internet traffic goes through routers.

RPG: role-playing game. A game (electronic or otherwise) in which the player assumes the role of a character in the game's simulated world.

RPN: reverse Polish notation. An arithmetic format in which the mathematical operator follows the numbers. Instead of "2 + 2" it's "2 2 +." RPN has been used in Hewlett-Packard calculators and the Forth programming language.

RS-232: a serial interface for attaching peripherals to computers, or for attaching computers to each other. The COM ports on PCs are RS-232 ports. RS-232 is a relatively slow interface; the maximum data transfer rate is less than 1Mbps.

RSA: Rivest-Shamir-Adelman. The surnames of three people who developed a public-key cryptography system in 1977. Their RSA algorithm is widely used in cryptography, usually for sending secret keys and digital signatures. Key lengths of 1,024 bits were considered secure, but the U.S. government now recommends using 2,048-bit keys as computer power continues to grow. See cryptography, AES, DES, 3DES, ECC, HMAC, SHA.

RSN: "real soon now," an optimistic estimate of when a new product will debut.

RSS: "really simple syndication." A software specification (actually a collection of specifications, not wholly compatible with each other) for automatically downloading data over the Internet. The data usually consists of frequently updated web pages, such as blogs. Users can subscribe to a website that supports RSS and automatically receive updates as they become available. See blog.

RTFM: "read the f**king manual," an admonition to users who can't figure out what to do. See BOFH, newbie.

RTL: register transfer level. Source code that represents an electronic circuit design and is used by EDA tools to generate a gate-level netlist, which in turn is used by other tools to create the masks for chip manufacturing.

RTOS: real-time operating system. A small operating system for embedded systems that runs fast enough to respond to real-time events. For example, an RTOS in an automobile must respond quickly enough to keep the engine from stalling or the antilock brakes from working.

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SaaS: software as a service. Subscription-based software, in which users pay a monthly or annual fee and receive periodic software updates over a network.


SAN: storage-area network. A subnetwork of stand-alone mass-storage devices (disk drives, tape drives, or CD-ROM jukeboxes) attached to a computer network without being part of a server. SANs can be more economical and reliable than file servers for central storage and backups. See NAS.

SAS: serial-attached SCSI (Small Computer System Interface). An interface for attaching mass-storage drives to computers. Introduced in 2005, the initial standard (SAS-1) operated at 3Gbps. Later versions have increased performance: SAS-2 (2009, 6Gbps) and SAS-3 (2013, 12Gbps). The future SAS-4 standard is targeting 22.5Gbps. See SCSI.

SATA: Serial Advanced Technology Attachment. An industry standard for disk drives adopted in 2001 that supersedes the older IDE bus and replaces bulky parallel cables with thinner serial cables. The SATA 1.0 (or SATA-I) standard delivers peak bandwidth of 1.5 gigabits per second (Gbps); SATA 2.0 (or SATA-II) delivers 3.0Gbps; SATA 3.0 (or SATA-III) delivers 6.0Gbps; and SATA 3.2 delivers 16Gbps. See ATA, IDE, EIDE, hard drive, mSATA, serial interface.

scanner: a computer peripheral that converts images into digital data. Flatbed scanners usually work with reflective images or objects, although some have transparency adapters. Film scanners work with photographic negatives or positives (slides).

scareware: a malicious computer program or false error message that tries to scare a user into thinking the computer is infected with malware or has suffered some other serious problem. Typically, the false warning intimidates the user into purchasing software that claims to fix the problem. But the problem is usually nonexistent, and the "repair" software is itself malicious. See malware, spyware.

scrape, scraper: see screen scraper.

screen scraper: a computer program that "reads" text screens displayed by other computer programs to collect data from them. Also known simply as a "scraper." Scraping has legitimate and illegitimate uses. Spammers often use scrapers to collect e-mail addresses posted on web pages. See spider, web crawler.

script kiddies: malicious hackers who have few computer skills but are able to attack computers and networks by following step-by-step instructions posted on mischievous websites. The "scripts" take advantage of well-known vulnerabilities in popular operating systems and rely on the ignorance or laziness of some system administrators. Script kiddies are also known as s'kiddies.

SCSI: Small Computer System Interface. Pronounced "scuzzy," SCSI is an interface for attaching mass-storage drives and other devices (such as scanners) to computers. It was popular in the 1980s and 1990s but has been largely replaced by Serial Attached SCSI (SAS) and SATA. See SAS, SATA, NVMe.

SD: Secure Digital. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. Maximum capacity is 2GB. Many cards describe their transfer speed using an "x" factor, in which 1x equals the transfer speed of the first CD-ROM standard (150KB per second). Example: 200x is 30MB per second. SD cards have been surpassed by the faster SDHC and SDXC cards. A physically smaller version of SD is the microSD standard.

SDHC: Secure Digital High Capacity. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. It extends the capacity of the previous SD standard to a maximum of 32GB. Many cards describe their transfer speed using an "x" factor, in which 1x equals the transfer speed of the first CD-ROM standard (150KB per second). Example: 300x is 45MB per second. SDHC cards have been surpassed by the faster SDXC cards. A physically smaller version of SDHC is the microSDHC standard.

SDK: software development kit. Software tools that help programmers write software for a specific system.

SDN: software-defined networking. The use of programmable hardware to perform networking functions previously performed by dedicated hardware. SDN allows more flexibility when allocating resources in data centers.

SDP: scenario design power. Intel's term for the typical power consumption of a microprocessor, based on an average software workload. Other chip vendors quote the equally vague "typical power" rating. See TDP.

SDXC: Secure Digital eXtra Capacity. A memory-card standard for digital cameras and other devices that need removable flash-memory storage. It extends the capacity of the previous SDHC standard to a maximum of 2TB. Many cards describe their transfer speed using an "x" factor, in which 1x equals the transfer speed of the first CD-ROM standard (150KB per second). Example: 600x is 90MB per second. A physically smaller version of SDXC is the microSDXC standard.

search engine: a program that helps users find information on the Internet. Users type a search word or phrase into the search engine, which then searches for the terms in a precompiled index of information. Google is a popular search engine. See spider.

Section 230: part of the Communications Decency Act of 1996 (47 U.S. Code § 230). This controversial section of U.S. Internet law grants legal immunity to website operators for libelous contributed content. Example: Facebook isn't liable for posts by its users that spread false or damaging information. In addition, Section 230 grants legal immunity to website operators who edit or delete contributed content. Example: users can't hold Twitter liable for removing their messages ("tweets") or for revoking their accounts. Contrary to widespread misinterpretation, Section 230 grants these immunities without distinguishing between "publishers" that moderate their content and "platforms" that don't. Also, Section 230 applies only to contributed Internet content, not to the website operator's own content, nor to print or broadcast content.

secure boot: a procedure that starts up a computer or other electronic device while verifying that the startup software hasn't been corrupted or compromised by a malicious hacker. ("Boot" is computer jargon for a startup procedure.) To be effective, secure boot requires special hardware built into the system's microprocessor. This hardware includes a digital key signature that verifies the authenticity of the startup software. Typically, the secure boot procedure runs a bootloader that in turn begins loading the operating system.

seek time: the time it takes for a disk drive to find a particular piece of data on the disk. Lower seek times are better, but it's only one factor in overall disk speed. The data-transfer rate—how fast the drive can retrieve the data—is also important.

selfie: a self-portrait made with a cell phone, tablet, or camera.

selficide: an accidental death while taking a selfie. Most selficides are caused by drownings, falls from high places, or transportation mishaps.

semiconductor: a material that can be either an electrical conductor or insulator, depending on the amount of current applied. Silicon is a semiconductor. Semiconductors are the basis for integrated circuits, such as microprocessors. See fabrication.

SEO: search-engine optimization. The craft of designing web pages that achieve higher rankings when search engines such as Google and Yahoo index the page and return search results. Because the search-engine companies reveal little about their ranking methods, SEO is largely educated guesswork.

Serial ATA: Serial Advanced Technology Attachment. An industry standard for disk drives adopted in 2001 that supersedes the older IDE bus and replaces bulky parallel cables with thinner serial cables. The SATA 1.0 (or SATA-I) standard delivers peak bandwidth of 1.5 gigabits per second (Gbps); SATA 2.0 (or SATA-II) delivers 3.0Gbps; SATA 3.0 (or SATA-III) delivers 6.0Gbps; and SATA 3.2 delivers 16Gbps. See ATA, IDE, EIDE, hard drive, mSATA, serial interface.

serial interface: an electrical connection between computers and peripherals that exchanges data by sending a bit-stream over a single wire, although additional wires are required for error correction and other purposes. Examples of serial interfaces in PCs are the RS-232 COM ports, USB, and Serial ATA. Antonym: parallel interface.

server: A computer that provides resources to client computers over a network. Usually a server stores applications and data files for access by clients. Some servers run large programs (such as database managers) and send results of queries to the clients. Web servers store web pages for access over the Internet.

server closet: a room that contains one or more servers.

server farm: a large group of servers, often dedicated to a specific application. For example, Google uses server farms to index the Internet for its online search engine.

servlet: a Java program that runs on a web server, usually for the purpose of adding functionality to a website. Technically, it's the opposite of a Java applet, which downloads from the server to the client computer and runs on the client.

set-top box: a device that provides additional functions with a TV. The simplest set-top boxes receive cable TV channels. More sophisticated boxes may decode digital TV signals, connect to satellite dishes, record TV shows, and even provide some computerlike functions, such as e-mail, web browsing, and videogames.

SETI@home is a program that runs on thousands of computers worldwide, sending results over the Internet to a remote server. A free download, the program runs in the background when a computer is idle, analyzing signals collected by radio telescopes. SETI means Search for Extraterrestrial Intelligence, a project started in 1999. This project looks for clues of intelligent radio broadcasts in the random background noise of the universe. Volunteers install the SETI@home program on their PCs to contribute processing time to this project. The general technique is called distributed computing, and similar programs are available for performing other tasks. See distributed computing, folding@home.

sexting: sending sexually oriented text messages via cellphone or instant messaging. The messages may or may not be welcomed by the recipient. The message is sometimes called a sext.

SGML: Standard Generalized Markup Language. A metalanguage for designing document markup languages. Markup languages describe the format of a document. XML and HTML are both derived from SGML, which is an international standard first adopted in 1986. SGML descends from Generalized Markup Language (GML), invented by IBM in 1969.

SHA: Secure Hash Algorithm. A method for digitally signing encrypted messages. Variations are SHA-1 (now considered vulnerable to attacks) and the SHA-2 family (SHA-224, SHA-256, SHA-384, and SHA-512, in ascending order of security). See HMAC, MAC.

shadowban: a method of censoring posts on social media without actually removing them or canceling the poster's account. A content moderator or automated algorithm may prevent the shadowbanned post from appearing in scrolling feeds or in search results. Technically, the post isn't censored, because it still exists in the system, but it's difficult to find. Shadowbanning is reportedly prevalent on TikTok and Facebook.

shallowfake: a poorly done fake video, the opposite of a deepfake. Example: In 2022, Russia altered a video address by Ukrainian President Volodymyr Zelenskyy to make it appear he was using cocaine. After much ridicule, Russia withdrew the fake video.

shareware: copyrighted software that is usually distributed freely but isn't fully functional until the user pays a fee to the owner. Shareware is not the same as freeware (which doesn't require a fee) or public-domain software (which isn't copyrighted or owned by anyone).

shell: a program that presents a different user interface than what the computer normally provides. A shell's interface is often graphical, although some shells are command-line interfaces. Typically, a shell makes the computer easier to use or provides access to additional capabilities.

shitcoin: derogatory term for an unstable cryptocurrency. See cryptocurrency, bitcoin, blockchain, stablecoin, hype coin, idiot coin.

shmoo graph: nickname for an engineering graph that shows performance characteristics. Shmoo graphs plot performance on two axes, usually as a diagonal line or step function. For a microprocessor, those axes may represent core voltage and clock frequency. (For obscure reasons, "shmoo" refers to a British cartoon character called a Schmoo.)

Shor's algorithm: a mathematical formula that theoretically can break public-key encryption when executed on a quantum computer. The algorithm effectively reduces the encrypted key's security by about one order of magnitude, so a 1,024-bit key is as easy to crack as a 128-bit key. The implications are severe, because the Internet uses RSA public-key encryption to protect commercial transactions and data transfers between websites and users. However, the U.S. National Security Agency (NSA) has said that a stable quantum computer capable of executing Shor's algorithm is unlikely in the near future. See RSA, quantum computing, AES, Grover's algorithm.

shoulder surfing: spying on someone's smartphone or computer screen.

shovelware: unneeded or unwanted software and other content loaded onto a CD-ROM or PC to increase the perceived value of the package. Usually the stuff is of low quality. See craplets.

shutter lag: the amount of time between pressing the shutter-release button on a camera and the actual capture of the image. Most digital cameras have an unreasonable amount of shutter lag, making it difficult to take peak-action photos.

Silicon Valley: a general area of the San Francisco peninsula in northern California that played a major role in the birth and growth of the semiconductor and computer industries. Seminal companies such as Shockley Semiconductor, Fairchild Semiconductor, National Semiconductor, Intel, Apple Computer, Sun Microsystems, and many others were founded there. Originally defined as the geographical valley between Palo Alto and San Jose, "Silicon Valley" now generally encompasses most of the San Francisco Bay Area. (Coined by the late Don Hoeffler in a 1972 article in Electronic News.)

SIM: subscriber identity module or subscriber identification module. A small memory card usually found in a mobile phone, although some other electronic devices use SIM cards as well. The card contains encrypted unique information about the owner/subscriber. In phones, it identifies the user to the network. See iSIM.

SIMD: single instruction, multiple data. A type of program instruction that allows a microprocessor to perform an operation on more than one piece of data at the same time. SIMD is especially useful for speeding up multimedia software that handles large amounts of audio, video, and graphics data.

simulator: a program that strives to recreate the behavior of an environment as closely as possible. Often the environment is something in the real world—for example, a flight simulator recreates the experience of flying an aircraft. Sometimes the environment is more abstract—a CPU simulator recreates the behavior of running a program on a different microprocessor.

single-precision floating point: A floating-point number represented in a computer by 32 bits. Commonly used in 3D graphics. See double-precision floating point, extended-precision floating point.

single source of truth: a trusted central repository that records financial transactions. Example: a bank is the single source of truth for all transactions involving the bank's customers. Some digital currencies such as bitcoin don't rely on this method; instead, they distribute the transaction records in shared files known as a blockchain.

singularity: a hypothetical future event in which computers become intelligent and self-aware, and perhaps capable of designing increasingly intelligent computers. In this scenario, humans could quickly become irrelevant. Some experts believe the singularity could happen in this century. See artificial intelligence, robopocalypse, foom, Turing test.

s'kiddies: see script kiddies.

skin: slang term for the graphical appearance or user interface of a computer program. Some programs, especially PC media players, allow users to customize the program's appearance by downloading and installing new skins. The term has been expanded to describe slip-on plastic covers for customizing the appearance of portable music players, cell phones, calculators, and other devices. See GUI, user interface.

SLA: stereolithography is a technology that some 3D printers employ to build objects using resin instead of plastic filaments as the raw material.

sleep mode: a state in which a computer, peripheral, or component consumes less electricity. Some devices enter sleep mode automatically after a set period of inactivity; other devices can be put to sleep by the user. Conserving electricity is especially important for battery-powered devices, such as portable computers.

SLI: Scalable Link Interface. A method of linking two or more graphics cards together in the same PC. Pioneered by a company called 3DFX, SLI originally stood for scan-line interleave before Nvidia acquired 3DFX and improved the technology. It remained troublesome, however, so Nvidia began phasing it out in 2020.

Slot 1: an obsolete interface for attaching Intel microprocessors to motherboards. Introduced with the Pentium II, it's a slot that accepts a daughtercard, which in turn contains the processor and external Level 2 (L2) cache. It's electrically compatible with Socket 8. Intel did not license Slot 1 to other processor makers. It runs at 66MHz or 100MHz.

Slot 2: an obsolete interface for attaching Intel microprocessors to motherboards. Introduced with the Xeon, it's a slot that accepts a daughtercard, which in turn contains the processor and external Level 2 (L2) cache. It's intended for servers because it's larger than Slot 1 and can hold more cache chips. Like Slot 1, it's electrically compatible with Socket 8. Intel did not license Slot 2 to other processor makers. It runs at 100MHz.

Slot A: an obsolete interface that attaches some of AMD's K7-class microprocessors to motherboards. Almost identical physically to Intel's Slot 1, it accepts a daughtercard that contains the processor and external Level 2 (L2) cache. It's not electrically compatible with Slot 1, however. AMD licensed the basic Slot A design from Digital. The initial version could run at 200MHz. It was superseded by Socket A.

SLS: selective laser sintering is a technology employed by some 3D printers to build objects by heating and fusing a powder as the raw material. Nylon is a popular material, but these printers are usually too expensive for most consumers.

SmartMedia: a standard format for flash-memory cards used in digital cameras, digital-audio players, and other electronic devices. It was popular in the early 2000s but is now obsolete. See flash memory, SD, Compact Flash.

SMP: symmetric multiprocessing. SMP systems have two or more microprocessors and an operating system that tries to distribute workloads evenly among the processors. Not to be confused with chip multiprocessing (CMP), which integrates multiple processor cores on a single chip—although CMP systems can do SMP.

SMT: simultaneous multithreading. A technique that allows a microprocessor to simultaneously execute instructions from multiple processes by mixing them together in the same execution pipeline. Normally, the processor would have to switch contexts to jump from one process to another. To the software, a single microprocessor appears as multiple microprocessors.

sneakernet: a "network" in which users exchange files among their unlinked computers by sharing removable disks.

SNN: spiking neural network. See neural network.

snow crash: a computer crash that leaves the screen filled with white static.

SoC: system on a chip. A highly integrated chip that includes almost everything needed to design an electronic product. SoCs usually include a microprocessor core, memory, and peripherals. Typical applications for SoCs are cell phones, MP3 players, and many other devices.

social engineering: the use of human psychology to circumvent security, usually by targeting a user. For instance, instead of penetrating a secure computer system or network to discover the passwords, a malicious hacker might simply phone a user, pose as someone from tech support, and ask for the user's password. See cracker, hacker, dumpster diving.

social media: websites that enable users to create personalized networks of friends or associates with whom they socialize online. Typically, users post updates of their life events and share photos and videos; other members of their network can post comments. Social media was pioneered by companies like Friendster and MySpace but now is dominated by Facebook for personal networking and LinkedIn for professional networking.

social network: a website designed for interaction among a community of people. Sometimes the participants share a common interest, but more often it's simply a network of friends, acquaintances, and colleagues. Examples are FaceBook and LinkedIn. Social networking is a key part of the Web 2.0 trend, in which websites are more interactive than the static websites of the past.

sock-puppet (also sockpuppet): a person who pretends to have an independent opinion but is fronting for someone else. The sock-puppet may be a paid or unpaid mouthpiece. Sock-puppets typically spread political propaganda on social media such as Facebook and in the comments sections of websites. U.S. intelligence agencies say the Russians and other foreigners used sock-puppets to influence U.S. public opinion and spread divisive discord before the 2016 presidential election. See bot, botnet, spam, zombie.

socket: a physical and electrical interface for a chip on a circuit board. Chips plug into sockets and communicate with other components by transmitting signals through their pins and the circuits etched onto the board. Some chips are soldered permanently in place without sockets.

Socket 370: a 370-pin CPU interface introduced by Intel in 1998. Sometimes it's called Socket 9, because Socket 8 was the Pentium Pro's interface and Socket 7 was for Pentium-class CPUs. Socket 370 superseded Slot 1. Some Pentium III and Celeron processors use Socket 370.

Socket 7: an obsolete interface for attaching x86-compatible microprocessors to PC motherboards. Originally designed by Intel for the Pentium, Socket 7 also worked with processors made by AMD, Cyrix, Centaur, and others. It was superseded by later sockets and slots because the I/O interface ran at only 66MHz.

Socket 8: an obsolete interface for attaching Intel Pentium Pro microprocessors to PC motherboards. It used a proprietary standard (known as the P6 bus protocol) shared by Intel's Slot 1 and Slot 2. It was superseded by those slots because it ran at only 66MHz.

Socket 9: unofficial term for a CPU interface introduced by Intel in 1998. It's called Socket 9 because Socket 8 was the Pentium Pro's interface and Socket 7 was for Pentium-class CPUs. More often it's called Socket 370 because it has 370 pins.

Socket A: an interface for attaching some of AMD's K7-class microprocessors (Athlon and Duron) to PC motherboards. Socket A superseded AMD's Slot A and is for K7-class processors that integrate the Level 2 (L2) cache on chip. See Slot A.

sockpuppet: see sock-puppet.

soft error: a transient error induced in a microprocessor or memory chip by an outside source, such as cosmic rays or electromagnetic emissions. Unlike software bugs or hardware-design faults, soft errors aren't deterministic (predictably repeatable), so they can be difficult to diagnose. Some critical computer systems have defenses against soft errors or even duplicate components that can take control if necessary.

SOHO: small office/home office. Often used to describe small businesses, self-employed knowledge workers, and telecommuters who use personal computer equipment.

SOI: silicon on insulator. SOI is an advanced chip-fabrication technology that enables faster transistor-switching speeds, and therefore higher-frequency (or lower-power) microprocessors. It works by adding an insulating layer to the transistor that reduces capacitance, so the transistor can change states more quickly. SOI was pioneered by IBM Microelectronics.

SON: self-organizing network. A cellular network of intelligent base stations that can communicate with each other to handle varying amounts of voice and data traffic. New base stations can be added without manually reconfiguring the network. See base station.

SONET: the Synchronous Optical NETwork standard defined by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI). Before SONET, first-generation fiber-optic networks used proprietary specifications; SONET defines industry standards for transmission methods and equipment. The SONET base signal (OC-1) is 51.84Mbps. Higher OC levels are multiples of the base signal. OC-3 is 155.52Mbps; OC-12 is 622.08Mbps; OC-48 is 2,488.32Mbps (2.43Gbps); and OC-192 is 9,953.28Mbps (9.72Gbps).

source code: the program instructions written by programmers. Programmers use a software-development tool to write, compile, test, and debug their source code. An assembler or compiler turns the source code into object code, which the computer executes. See assembler, compiler, object code.

south bridge: the part of a PC system chipset that connects the north-bridge chip to other system devices. The south bridge—which may consist of one or more chips—typically connects to the serial ports, parallel port, USB ports, keyboard/mouse ports, and other system interfaces. See core-logic chipset, north bridge.

spaghetti code: derogatory term for source code that frequently jumps from one place to another within a program, making it difficult for programmers to follow the logic. This was particularly a problem with older BASIC dialects that relied heavily on the GOTO statement, which jumped directly to a numbered or labeled line of code. Structured programming languages such as Pascal were less prone to spaghetti code, but modern object-oriented languages with their deeply nested class hierarchies seem to have resurrected the problem. See source code, BASIC, Pascal, Java, C++, OOP.

spam: unwanted e-mail, usually mass-mailed advertising. Spam is the counterpart of paper junk mail. See spammer, j-mail, spim.

spammer: someone who sends spam (unwanted mass e-mail).

spamouflage: spam disguised as legitimate e-mail to evade anti-spam filters. See j-mail, spam, spammer.

SPDIF or S/PDIF: a digital audio interface. Connecting two digital audio devices with an S/PDIF cable preserves sound quality by keeping signals in the digital domain; otherwise, signals would have to pass through a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC) at each end. There are two types of S/PDIF physical interfaces. One is electrical and uses standard RCA connectors (phono connectors). The other is optical for fiber-optic cables.

spear phishing: a phishing attack aimed at a specific person or group of people instead of the public at large. Often, employees of a particular company are the target. Russian agents used this trick to steal email messages from the Democratic National Committee in 2016. See phishing, vishing.

SPEC: Standard Performance Evaluation Corporation. An independent industry organization that measures and publishes the performance of microprocessors, workstations, web servers, mail servers, graphics, and Java virtual machines. SPEC uses both synthetic and application-level benchmark programs. See

speculative execution: the ability of a microprocessor to fetch and execute instructions beyond a conditional branch before knowing the outcome of the branch. It's a refinement of branch prediction that relies heavily on accurate predictions. Wrong predictions may incur heavy penalties in wasted clock cycles when the processor must discard the speculative results. The processor always holds the speculative results until confirming whether or not the branch was taken.

SpeedStep: a power-saving feature in some Intel x86 processors for notebook computers. The first version of SpeedStep automatically lowers the chip's supply voltage and frequency when the notebook runs on batteries. It raises the voltage and frequency to normal levels when the notebook runs on AC power. Enhanced SpeedStep, introduced in 2003 with the Pentium M, is more sophisticated; it automatically varies the chip's voltage and frequency in response to software demands. See LongHaul, LongRun, PowerNow.

SPICE: Simulation Program with Integrated Circuits Emphasis. A software tool that helps electrical engineers design circuits and chips.

spider: a program that methodically follows hyperlinks to access every page on a website and index the words it finds. Search engines use spiders to build indexes of information on the Internet, then search the index in response to user queries. Spiders are also known as web crawlers. See screen scraper.

spim: unwanted (usually commercial) messages that arrive over an instant messaging service. Derived from "spam + IM". See spam, IM, j-mail.

spintronics: the use of a quantum property of electrons (their spin) for storing data or building digital logic circuits.

spoofing: disguising e-mail messages or network packets so they appear to originate from a different source. Spoofed e-mail is usually spam or attempted fraud. A spoofed packet is like a spy carrying a fake ID; malicious hackers sometimes use this technique to attack systems and prevent network administrators from filtering out packets that are causing trouble. See cracker, hacker, j-mail, spam.

spyware: software that secretly runs on a computer to collect information. The party who planted the spyware may use the information for malicious hacking, espionage, fraud, or commerce. Often the spyware uses the computer's network connection to secretly transmit the information back to the spyware's owner. Some commercial spyware accompanies the installation of legitimate software.

SQL: Structured Query Language. A formal set of rules for submitting queries to computer databases. By formatting a request in SQL, users can retrieve specific information. See database, database engine, query engine, Boolean logic.

SRAM: static random-access memory, a very fast type of memory that's often used for caches and video memory. Unlike DRAM (dynamic random-access memory), it doesn't require a periodic refresh signal to maintain its state, although like DRAM it is volatile (all data is lost when the power shuts off). SRAM is generally too expensive to use for main memory in a computer because it needs six or more transistors per memory cell instead of the one transistor per cell in DRAM.

SSD: solid-state drive. A "disk drive" that stores data in flash memory instead of on spinning magnetic platters. SSDs are more costly than conventional disk drives but are becoming popular for systems needing high performance or ruggedness.

SSE: Streaming SIMD Extensions, the 70 new instructions and 8 new registers that Intel first added to the Pentium III processor in 1999. Most of the instructions speed up 3D graphics, but they also accelerate other operations. See MMX, SIMD, SSE2.

SSE2: Streaming SIMD Extensions 2, the 144 new instructions that Intel first added to the Pentium 4 processor in late 2000. SSE2 instructions speed up 3D graphics and other floating-point and multimedia tasks. Many are 128-bit extensions to existing SSE and MMX instructions, and they use the SSE registers. See MMX, SIMD, SSE.

SSL: Secure Socket Layer. A security protocol developed by Netscape that allows a web browser to make an encrypted connection with a web server. Commercial websites often use SSL to protect online commerce transactions. See TLS, DES.

stablecoin: generic term for a digital currency linked to a sovereign currency or hard commodity to reduce fluctuations in value. The term is now considered misleading after the catastrophic collapse of some stablecoins, such as TerraUSD in 2022. See cryptocurrency, bitcoin, blockchain, hype coin, idiot coin, shitcoin.

stack: (1) memory that a microprocessor uses to temporarily store numeric values or memory addresses; (2) a hierarchical set of software that provides various functions in a computer or other electronic device. Machine-level or assembly-language programmers generally use the first definition; the second is a common industry term. Example: the "network stack" is the low- and mid-level software that enables a high-level application (such as a web browser or email reader) to communicate over a network.

staircasing: the visibly jagged effect of pixels in a digital image, especially apparent when viewing the square or rectangular pixels along the edge of a curved line. Smaller pixels (higher resolution) is the cure; anti-aliasing helps, too. Staircasing is also called "jaggies." See pixel, pixelated.

stealth mode: the period when a start-up company remains secretive before revealing its products or technology.

steampunk: a subgenre of science fiction that reimagines the Victorian Age with new inventions, or that projects a different present or future based on such inventions. (The term derives from the steam power of Victorian technology and the cyberpunk fiction that became popular in the 1980s.) Steampunk novels draw inspiration from actual Victorian science fiction, such as The Time Machine (H.G. Wells, 1895) and Twenty Thousand Leagues Under the Sea (Jules Verne, 1870). A popular modern example is The Difference Engine (William Gibson and Bruce Sterling, 1990). Steampunk also describes an artistic style that imitates the look of Victorian machinery. See cyberpunk.

steganography: hiding data by encoding it in the least-significant bits of each byte in a data file. The hidden data may be a secret message or a copyright notice. The data file may be an image or a sound file. Also known as digital watermarking.

stego: see steganography.

STEM: science, technology, engineering, mathematics. Academic subjects that some people believe are underemphasized in our schools.

storage: also known as "mass storage," any device for recording information for use by a computer system. Some mass-storage media (such as CD-ROMs) are read-only—the recorded data is permanent and can't be deleted or changed. Write-once media (such as CD-Rs) can store data, but they cannot be erased or changed. Read/write media (such as CD-RWs and most magnetic disks) can be erased and changed many times. Common mass-storage devices are hard disk drives, floppy disk drives, and CD drives. They may store programs and data files.

streamies: people who listen to streaming audio over the Internet. See streaming.

streaming: sending continuous data over a network as a stream of packets that are interpreted individually instead of being collected and reassembled into a self-contained file. Streaming is typically used for audio and video, which can be experienced in real time as the packets arrive. Without streaming, the client system must receive the whole package as a file before using it.

submicron: less than one micron. Usually refers to chip-fabrication processes that have an L-effective gate length of less than one micron.

subroutine: a block of instructions in a program that carries out a frequently needed task. By organizing the instructions into a subroutine, programmers can call the subroutine by name whenever necessary, eliminating redundant code. Subroutines are also known as functions, procedures, subprograms, and methods.

Super 7: an obsolete refinement of the Socket 7 microprocessor interface for attaching x86-compatible processors to system motherboards. Super 7 can run at 100MHz, or 50 percent faster than Socket 7's 66MHz.

supercomputer: a very large, powerful, expensive computer designed for heavy-duty number crunching, usually for scientific applications. Supercomputers are the largest breed of computing machines, often filling huge rooms. They are typically used for medical research, astronomy, economics, weather/climate forecasting, financial modeling, simulations, cryptography, and military applications. Modern supercomputers are built with thousands of microprocessors in a massively parallel configuration. See mainframe, microprocessor, massively parallel.

superpipeline: a long instruction pipeline in a microprocessor—usually more than ten stages. Superpipelining is a way of achieving higher clock speeds, but one drawback is a greater penalty for taking or mispredicting a conditional branch. The most-superpipelined processor seen to date is Intel's Pentium 4, which has a pipeline at least 20 stages deep. See hyperpipeline.

superscalar: multiple-pipelined instruction execution in a microprocessor. A superscalar processor can execute more than one program instruction at a time (one in each pipeline), thanks to multiple function units. See function unit, pipeline, uniscalar.

swatting: the prank of summoning a police SWAT (Special Weapons and Tactics) team to a home or workplace by phoning the emergency 911 line and falsely reporting a crime in progress at that address. Often this illegal practice is retribution for a real or imagined offense against the caller, but sometimes the target is random. In December 2017, a SWAT team in Wichita, Kansas shot and killed an unarmed innocent man whose home address was reported to the Wichita police by a Los Angeles prankster who falsely claimed a murder had occurred there. The victim was a stranger apparently chosen at random by the prankster. See dox, doxxing, trolling.

switch fabric: a dense network of connections for sharing data among components. Switch fabrics may be found in computers (especially servers), routers, or even inside chips. Sometimes called a mesh.

syntax error: a spelling or grammatical error in the source code of a program. Syntax errors are usually flagged by a compiler. The compiler won't convert the source code into object code until a programmer fixes the errors.

system chipset: two or more chips on the motherboard of a PC that connect the microprocessor to other system devices. The system chipset defines many of the features of a PC: how much main memory (RAM) it can use, how many expansion slots it has, the types of system interfaces available, how much memory it can cache, and so forth. System chipsets for PCs are usually partitioned into two sections known as the north bridge and south bridge. The system chipset is also known as the core logic.

system I/O bus: the main input/output bus on a microprocessor. This interface may connect the CPU to main memory and other system devices. In PCs, the system I/O bus is known as a frontside bus and connects to the core-logic system chipset.

system on a chip: an SoC is a microprocessor chip with extra functions normally provided by auxiliary chips and components. Those functions might include memory control, peripheral interfaces, graphics, sound, and more. Such highly integrated chips are usually designed for low-cost PCs or non-PC embedded systems.

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tag RAM: memory chips that store memory addresses for use by a microprocessor's Level 2 (L2) or Level 3 (L3) cache. The memory addresses point to locations in main memory from which the data in the cache came from. Without enough tag RAM, the cache can "see" only a limited amount of the system's total memory.

TCO: total cost of ownership, the actual cost of a product over its lifetime. Example: the TCO of an operating system includes not just the retail price of the software license, but also the labor costs of installation, ongoing maintenance, and troubleshooting.

TCP/IP: Transmission Control Protocol/Internet Protocol, international standards that govern how computers can send information over data networks. The Internet is an example of a network that uses TCP/IP. Local-area networks (LANs) may use different standards.

TDP: thermal design power. Intel's definition of near-maximum power consumption for a microprocessor or companion chip. System designers use TDP to determine how much power and cooling the system needs. In extreme cases, power consumption can exceed TDP. See SDP.

technobabble: a dismissive term for the kind of terms found in this dictionary.

telecommuter: a person who works at home by using a personal computer and network connection instead of commuting to an office. A telecommuter may be employed by a company or self-employed.

telematics: using two-way wireless communications with automatic location identification (usually via GPS) to provide some kind of remote service. Example: GM's OnStar system that allows remote door unlocking and emergency-service dispatching when the motorist contacts the OnStar operator from an automobile. See GPS.

terabit: 1,024 gigabits, or 2^40 bits. Abbreviated Tb. See bit, byte.

terabyte: 1,024 gigabytes, or 2^40 bytes. Abbreviated T, TB, or tB. See bit, byte.

teraflops: one trillion floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called TFLOPS. See FLOPS, floating point, FPU.

textures: the surface graphics on a simulated 3D object. Without textures, on-screen 3D objects look like naked skeletons of polygons. Textures add realism—a brick wall, the skin of a lizard, or the gleaming metal surface of a spaceship. A 3D program stores a texture as a graphics pattern and applies it to the structure of polygons.

texture mapping: applying textures to simulated 3D objects in computer graphics.

TFLOPS: one trillion floating-point operations per second. A measure of arithmetic performance on a microprocessor or computer. Also called teraflops. See FLOPS, floating point, FPU.

thread: a path of execution through a computer program. It's the sequence of program instructions that the computer carries out. Early, simple programs merely ran from start to finish, but modern programs jump and loop through many possible paths. A multithreaded program has multiple threads running at once. See multithreading.

threadlock: a software bug that stalls two or more threads running within a multithreaded program. A condition arises in which a thread must wait for another thread to finish a task, but the first thread is likewise waiting; neither can proceed. The computer appears to freeze. Also called a deadlock.

three-finger salute: slang term for pressing the key combination Ctrl-Alt-Del (Control-Alternate-Delete). On IBM PC-compatible computers running MS-DOS or older versions of Microsoft Windows, this key combination forces the computer to restart. Beginning with Windows NT, this key combination opens the Windows password log-on or the Windows Task Manager. Users typically resort to this emergency procedure (which takes three fingers to initiate) when a program malfunctions and freezes the computer. The key combination was invented in 1981 by Dr. Dave Bradley, an engineer developing the first IBM PC. Bradley chose these keys because they were the most widely separated keys on the original IBM PC keyboard and hence were almost impossible to press by accident.

Three Laws of Emulation: "(1) Any computer can emulate any other computer as long as speed is not a consideration; (2) Any computer can emulate any other computer as long as cost is not a consideration; (3) In general, therefore, forget about emulators." These semi-serious "laws" were proposed by Compute!'s Gazette magazine in the August 1987 issue in response to reader interest in emulating their 8-bit computers on newer 16-bit computers. In general, the 16-bit computers weren't fast enough to emulate the 8-bit machines at their full speed. To answer a skeptical reader's letter, the magazine (which covered 8-bit Commodore computers) expanded on this subject in the October 1987 issue. See emulator.

thumb drive: a small data-storage device that contains flash memory and that plugs into a USB port. The port provides electrical power and transfers data to and from the thumb drive. Despite the anachronistic word "drive"—a holdover from storage devices that use spinning disks—a thumb drive requires no moving parts. The data resides in solid-state flash memory (transistors) and is nonvolatile, which means the drive retains the data even when unplugged from the USB power source. Flash memory isn't infinitely nonvolatile, however; over time, the transistors gradually lose their charge. See flash memory, volatile, USB.

Thunderbolt: a serial interface developed by Intel and Apple for attaching peripherals to computers. It debuted in 2011 as Light Peak, then was renamed Thunderbolt. The Thunderbolt-1 specification operated at 10 gigabits per second (10Gbps) in each direction and used the same physical connector as Mini DisplayPort. Thunderbolt-2 (2013) also used that connector but could join the two channels to provide 20Gbps in either direction. Thunderbolt-3 (2015) adopted the same physical connectors as USB-C, raised the data rate to 40Gbps, and is compatible with the USB4 standard. The latest Thunderbolt-4 specification (2020) runs at the same speed as Thunderbolt-3 (40Gbps) but supports at least two 4K-resolution video displays instead of at least one and adds other features, such as 40Gbps cables up to two meters long. It also complies with the USB4 standard. See USB, serial interface, 4K.

thunking: a software operation that switches between two different memory-addressing schemes or instruction formats. For example, modern 32-bit versions of Microsoft Windows can run older 16-bit Windows software by "thunking" or translating the 16- and 32-bit program code. Thunking is also a technique used by some microprocessors that recognize multiple instruction formats, such as 16- and 32-bit instructions. Thunking usually has some overhead that slows performance.

time sink: an activity that wastes time. Derived from heat sink.

TKL: TenKeyLess—a computer keyboard that saves space by omitting the numeric keypad and associated keys. Favored especially by gamers.

TLA: three-letter acronym (like this one).

TLS: Transport Layer Security. A security protocol that allows a web browser to establish an encrypted connection with a web server. A commercial website might use TLS to protect online commerce transactions. See DES, SSL.

TOR: The Onion Router. TOR is a program that uses multiple levels of encryption to keep Internet users and their communications anonymous. If another party intercepts the network traffic, the encryption prevents eavesdropping on the content. Also, unlike conventional web browsers, TOR conceals information that could be used to identify the user or the user's physical location. TOR has legitimate applications for people who wish to remain anonymous on the Internet but also is popular with malicious hackers, criminals, and spies. The TOR Project was started by the U.S. government and still receives government funding. See darknet.

TPM: Trusted Platform Module. A chip (or part of a chip) that strengthens computer security. It can securely create and store the mathematical "keys" for cryptography. Embedding these vital functions in hardware instead of software prevents malicious tampering. PCs began implementing the TPM 1.2 standard in 2006, but many computers disable it by default. The current TPM 2.0 standard debuted in 2016 and is required to run Windows 11. See crypto.

traffic shaping: using network routers to apply delivery priorities to data packets traversing the Internet, based on the content, source, or destination of the packets. Example: packets carrying time-sensitive data for audio/video streams and online games could get higher priority than packets carrying e-mail, which can tolerate slower delivery. Traffic shaping is controversial, because it conflicts with "net neutrality," which favors government regulation to enforce equal treatment for all packets on the Internet, regardless of their nature or the effect on network traffic. See Internet, network, net neutrality, packet, packet switching.

transceiver: a transmitter/receiver. In computer terminology, it's usually a chip or part of a chip that exchanges data over an interface.

transform matrix: a set of numbers required to redraw a simulated 3D object on the screen. When an object moves, or when the user's viewpoint of the object changes, the computer must redraw the object. It starts by recalculating the coordinate matrix for every vertex, using a process called matrix multiplication. Usually the transform matrix is a 4x4 arrangement of 16 numbers and the coordinate matrix is a 1x4 set of four numbers.

transistor: the basic building block of semiconductor integrated circuits. It works as a switch to direct the flow of electrical signals or as a valve to regulate current flow.

Trash-80: derogatory term for the TRS-80 computers sold by Tandy Radio Shack in the 1970s and 1980s. See TRS-80.

TRNG: true random-number generator. Some microprocessors have special hardware for generating the random numbers essential to cryptography and other security functions. Although software programs can generate random numbers, the results are called "pseudo-random" because they usually follow a pattern and may eventually repeat. Strong security requires true randomness. To generate these numbers, the processor may use various techniques, such as sampling background noise in its circuits to obtain a random value that "seeds" the number generator.

Trojan horse: a program that disguises its true purpose, usually for malicious intent. Most Trojans pretend to be normal programs but secretly attempt to damage the computer's data in some way. Unlike a virus, a Trojan doesn't automatically replicate itself or attach itself to another program. See cracker, hacker, malware, virus, worm.

troll: slang for a posting in an Internet newsgroup or chat room deliberately intended to provoke angry responses from other participants. See trolling, flame, flame war.

trolling: harassing someone in retribution for a perceived offense. Often this practice starts by spreading the target person's email address, phone number, and home and/or work address to a group of followers who barrage the target with abusive messages and threats. It may also include spreading the target's personal information to encourage identity theft. See troll, dox, doxxing, swatting.

TRS-80: brand name for a variety of personal computers sold by Tandy at Radio Shack stores in the 1970s and 1980s. "TRS" stands for "Tandy Radio Shack" and "80" stands for "Z80," the eight-bit microprocessor used in the first TRS-80 introduced in 1977. Later models shared the TRS-80 brand name even if they used different processors and were incompatible with each other. The original TRS-80 Model 1 was among the first three personal computers introduced in 1977 that were available off the shelf and didn't require assembly. Together with the Apple II and Commodore PET, the TRS-80 Model 1 helped move computing beyond the electronics-hobbyist era toward mass popularity. See Apple II, PET, Trash-80.

Turing test: a test proposed in 1950 by Alan Turing (1912-1954) to determine if a computer has achieved humanlike intelligence. The test is a text-based conversation between a human, another person, and a computer posing as a person. If the first person can't tell which other party is the computer, the machine passes the Turing test. Today, the test is no longer considered valid, because computers have passed it without demonstrating other characteristics of true intelligence. See artificial intelligence, singularity, robopocalypse, foom.

turnkey or turn-key: something simple or automatic that requires little or no expertise to install or use. A "turnkey solution" might be a software program or hardware/software package that performs an important function and (supposedly) is as easy to implement as turning a key in a lock.

tweet: a brief public message sent via Twitter, an Internet-based messaging service.

typo squatting: the practice of reserving a second-level Internet domain name that's a slightly misspelled version of a popular domain, such as "" instead of "" The reason may be to spoof the legitimate website, perhaps for malicious purposes. See cybersquatter.

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UAC: user account control. The means by which an operating system controls the level of security access for different users on a computer. Usually, the highest access level is "administrator"; regular "user" accounts have less access. UAC prevents lower-level users (as well as guest users and malware) from changing critical files and programs. See operating system, malware.

UART: universal asynchronous receiver/transmitter, the electronic circuitry for a serial port. It converts bytes into a serial stream of bits and vice versa.

Ubuntu: a popular version of the GNU/Linux operating system for computers. It was created in 2004 by Mark Shuttleworth, a South African. ("Ubuntu" means "humanity" in Zulu.) It includes a graphical desktop and all of the system software and application software to make a complete ready-to-use system, also known as a "distribution" or distro. Ubuntu is a derivative ("fork") of Debian, an earlier distro. Ubuntu has also spawned forks, such as Kubuntu, Xubuntu, and Mint. See Linux, GNU, kernel, Unix.

UHDTV: Ultra High Definition Television. An international standard that defines the size and shape of TV and video screens and is the successor to High Definition Television (HDTV). UHDTV resolution is 3,840 x 2,160 pixels, which yields the same 16:9 aspect ratio as HDTV's highest resolution (1,920 x 1,080 pixels). In the consumer market, UHDTV has become synonymous with 4K, which technically has slightly more resolution. See HD, 4K, pixel, aspect ratio.

UI: see user interface.

UIDL: unique identity list, a POP3 command that allows a mail server to keep track of downloaded and deleted messages. Sometimes a reference to UIDL appears in error messages with e-mail clients that don't support it. See POP3.

UMPC: ultramobile personal computer. A project backed by Intel, Microsoft, and many other companies to popularize Windows-compatible PCs that are smaller and more portable than notebook PCs. A key feature is universal wireless Internet connectivity.

uncanny valley: the perceived gap between a robot built to look human and one that is indistinguishable from a human. Some people feel uneasy when a robot built to look human slightly fails that goal. Robotics experts generally believe it's better to make a robot look mechanical than to fall short of looking completely human. Others disagree, however.

uncore: support logic and memory surrounding a microprocessor core. Intel seems to have coined this odd word. When describing a microprocessor chip's silicon area, Intel sometimes refers to "core area" (the actual processor core) and "uncore area" (other components and caches attached to the processor core). See core, cache, microprocessor.

underclocking: lowering a microprocessor's performance, power consumption, and heat dissipation by running it at a lower clock frequency than its nominal rating.

uniscalar: single-pipelined instruction execution in a microprocessor. A uniscalar processor can execute only one instruction at a time. Sometimes called simply "scalar." See pipeline, superscalar.

Unix: (pronounced "YOO-niks") an operating system that runs on a wide variety of microprocessor architectures. It was originally developed by AT&T in 1969, but several independent versions now exist, with various degrees of compatibility. Examples include Solaris (Sun), IRIX (SGI), and AIX (IBM). GNU and GNU/Linux are similar to Unix.

unobtainium: engineering slang for a mythical substance that solves a difficult design problem. Example: "I could run this microprocessor at twice the clock frequency if only I could replace the aluminum interconnects with unobtainium."

UPS: uninterruptible power supply. A large backup battery that allows computers and other equipment to run after a general power failure. The UPS also protects equipment from power spikes. A typical consumer UPS may have enough battery power to run a desktop computer for only a short time, but it's long enough to save work and shut down gracefully.

uptime: the amount of time a computer spends up and running; often used as a measure of availability or reliability for servers. See downtime, five nines.

URL: uniform resource locator. The address of a computer on the Internet, as in "". Actually, URLs are aliases for numerical IP (Internet Protocol) addresses, which are more difficult to remember and type in. See DNS, IP.

USB: Universal Serial Bus. An industry-standard serial interface introduced in 1995 for computers, peripherals, and other devices. USB 1.1 reaches 12 megabits per second (12Mbps) and is suitable for low-speed peripherals (keyboards, joysticks, printers, mice), but it's less suitable for high-speed devices such as hard disk drives. The second version, USB 2.0 Hi-Speed, is 40x faster (up to 480Mbps) and is backward compatible with USB 1.1. The third version, USB 3.0, adds a SuperSpeed transfer rate that can reach 5Gbps (5 gigabits per second, or 5,000Mbps). USB 3.1 doubles the SuperSpeed rate to 10Gbps while still supporting the 5Gbps standard. It also introduced a new connector (USB-C) that's backward compatible with older USB devices and cables. USB 3.2 (2017) keeps all those standards and adds a doubled SuperSpeed+ rate of 20Gbps that requires the new connector. The current version, USB4 (2019) and doubles the speed again to 40Gbps using the same USB-C connector. The newest version, USB4 2.0 (2022) boosts the maximum speeds to 80Gbps and 120Gbps. Because USB4 can carry data, display signals, and power, it may become the only type of connector and cable most computers need. See serial interface, Thunderbolt.

user interface: the controls for operating computer software or any hardware device. User interfaces may be graphical, textual, or physical. See command-line interface, GUI, skin.

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vaporware: a hardware or software product that is announced by a company but isn't ready to ship. Sometimes it never appears on the market or is less capable than promised.

VAR: value-added reseller. A computer dealer that doesn't just sell factory-made PCs, but that also provides services (such as installation, tech support, etc.) or builds custom PCs to order.

variable: a placeholder in a computer program that represents a value stored in memory. The variable jan_sales might represent the dollar amount of company sales in January. Variables can be added, subtracted, multiplied, divided, and manipulated in numerous other ways. Variable names are chosen by programmers and are shorthand substitutes for actual memory addresses.

Verilog: an abstract language that engineers use to design electronic circuits and systems. It resembles a software programming language such as C. Another popular language of this sort is VHDL. Verilog tends to be more popular in Silicon Valley.

vertex: a corner of a polygon used to draw simulated 3D graphics on the screen. Polygons are usually triangles or rectangles, which have three or four vertices, respectively. When an object moves, or when the user's viewpoint of the object changes, the computer must recalculate the new position in virtual space of each vertex. It does this with a process called matrix multiplication.

VHDL: VHSIC hardware description language. An abstract language that engineers use to design electronic circuits and systems. It resembles a software programming language such as C. Another popular language of this sort is Verilog. VHDL tends to be more popular outside Silicon Valley.

VHSIC: very high-speed integrated circuit. See IC, VHDL.

video memory: temporary memory that a processor or coprocessor uses to display graphics on the screen. Usually this memory consists of several chips on the graphics card. It's not counted as part of a PC's main memory. Also called a frame buffer.

virtual filespace: The sum total of all mass storage devices accessible from a computer. For computers not attached to networks, the filespace consists of local devices only. Networked computers have access to remote servers (and sometimes other clients) on LANs, WANs, or the Internet.

virus: a self-replicating program that attaches itself to another program, usually for a malicious purpose. Unlike biological viruses, computer viruses don't evolve on their own; they are written by programmers. Most viruses are designed to damage a computer's data in some way. See cracker, hacker, malware, Trojan horse, worm.

vishing: voice phishing. Similar to phishing, except instead of tricking the victim with a fake email or text message, the attacker makes a phone call asking for a username, password, or other security information. Typically, the attacker (visher) poses as a legitimate authority when requesting this private info. See phishing.

Vista: a major new version of the Microsoft Windows operating system introduced in 2007. Widely derided for its bloat and disappointing performance, Vista was replaced by Windows 7 in 2009. See Windows, operating system.

VLIW: very long instruction word. It's a design approach to microprocessors that tries to increase the number of program instructions executed simultaneously while keeping the chip as simple as possible. The term refers to the instruction format—multiple instructions are bundled together into long "words."

vlog: a video blog. Vlogs are web pages offering video clips, usually brief and personal, like video diaries. Vlogging is the video equivalent of blogging. See blog, weblog.

VoIP: voice over Internet Protocol. A method of transmitting a conversation over the Internet instead of conventional telephone lines. A computer at each end of the VoIP connection converts the audio into digital data, divides the data into IP packets, and sends the packets over the Internet to the other computer. See IP, packet, TCP/IP.

volatile: computer memory that loses its data when the electricity shuts off. DRAM and SRAM are volatile; ROM and flash memory are nonvolatile. Sometimes this term describes temporary mass storage or any temporary data that isn't saved. See DRAM, flash memory, SRAM, ROM.

VPN: virtual private network. A private computer network that may span great distances, up to global in scope, using the public Internet instead of private leased lines. VPN traffic is encrypted to prevent snooping. See WAN.

VR: virtual reality. An artificial environment created on a computer. This term often describes VR goggles or glasses, which replace the wearer's view of the real world with images of an artificial world. They allow the wearer to physically move about the artificial environment as if it were real. Videogames are a typical application. By contrast, AR goggles or glasses superimpose data on the wearer's view of the real world. See MR, XR.

VRM: voltage regulation module. An electrical component on computer circuit boards that reduces and regulates the voltage of power supplied to other components, such as the main processor.

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wafer: a crystalline disc on which semiconductor chips are fabricated. The wafers are cut into individual chips. Most wafers use silicon for the semiconductor layer and copper or aluminum for the conductor layers. The first wafers in the 1960s were the size of coins. The largest wafers today are 300mm (12 inches) in diameter. Larger is better, because more chips can fit on them, reducing manufacturing costs. See chip, fab, fabrication.

wall wart: derogatory term for the bulky AC adapters required by many portable computers and electronics products.

WAN: wide-area network. A private computer network that spans large distances, up to global in scope. Usually a WAN connects LANs in multiple locations. A large company might use a WAN to unite the LANs in all its offices. Some WANs use the public Internet for this purpose; see VPN.

WAP: Wireless Access Protocol, a standard that allows mobile phones, pagers, PDAs, and other wireless communication devices to access special content on the Internet. WAP is based on WML, which in turn is based on XML. A competing wireless data-access protocol is i-Mode.

warchalking: using chalk or other improvised means to informally mark the location of an access point for a publicly available wireless network. See 802.11, hotspot, Wi-Fi, WLAN, wardialing, wardriving.

wardialing: using an automated program to call every telephone number in a local exchange or area to find computers with auto-answer modems, usually as a prelude to penetrating the computers. It's less common nowadays because most computers set up for remote access have broadband Internet connections. The term was derived from WarGames, a 1983 movie in which a teenager uses the technique to penetrate a military computer. See warchalking, wardriving.

wardriving: cruising a neighborhood in a motor vehicle while using a mobile computer to search for openly accessible wireless networks. Often the access points are unprotected private networks, ripe for penetration. See warchalking, wardialing, 802.11, hotspot, Wi-Fi, WLAN.

warez: pirated commercial software distributed by unlawful means.

warspying: using a directional antenna and wireless video receiver to scan a neighborhood for wireless video-surveillance cameras that operate in the 2.4GHz radio-frequency band. X10-standard cameras are particularly vulnerable to this technique. Also called warviewing. See warchalking, wardialing, wardriving.

watermarking: see steganography.

web: shorthand for the World Wide Web.

Web 2.0: the second coming of the World Wide Web, following the bust of the tech bubble in 2000. This amorphous term may describe companies, business strategies, technologies, or services. Some Web 2.0 companies are actually Web 1.0 companies (Amazon, Google, Yahoo) that survived the bust. Web 2.0 strategies, technologies, and services tend to favor more user interaction with a website, instead of static web pages.

web crawler, webcrawler: see spider.

webcam: a video camera that feeds a live signal over the Internet that other people can view with a web browser.

webcast: a broadcast over the World Wide Web. A webcast may or may not include live video; some webcasts are relatively static presentations.

webinar: a seminar delivered over the World Wide Web. Usually a webinar has presentation slides and streaming audio, and sometimes animation or streaming video. It may be canned (prerecorded) or live.

weblog: an online journal, commonly known as a blog. Some blogs consist entirely of musings by the author, while others accept comments from visitors to the website. The act of posting messages is called blogging; the poster is known as a blogger. Lately, the term "blogger" is also being applied to online journalists (often amateurs, in the sense that they are unpaid) not associated with a traditional media outlet. See blogosphere, reality media, vlog, wiki.

webmaster: the person in charge of a website. He or she may also be the person who designs the web pages and writes any programs that help it run.

WebPad: a hand-held, battery-powered computer with a large LCD screen but no traditional keyboard. It connects wirelessly to the Internet. WebPads are intended to replace PCs for some mobile applications.

website: one or more web pages hosted on the Internet, usually organized by topic. Websites are typically created and maintained by companies, governments, educational institutions, nonprofit organizations, and individuals. Each website has a unique address on the Internet and resides on one or more web servers. See Internet, World Wide Web.

WFH: work from home. Also called telecommuting. It gained popularity under shelter-in-place orders during the Covid-19 pandemic of 2020.

White-Fi: unofficial name for a wireless network that uses the normally vacant "white space" radio-frequency spectrum between broadcast TV channels. "White-Fi" plays on the Wi-Fi name for existing wireless networks that use much higher radio frequencies. In the 1940s and 1950s, the white space was intentionally reserved to prevent interference between TV channels next to each other in the radio-frequency spectrum. Now some companies (such as Microsoft) claim that modern technology enables wireless networks to use that vacant spectrum without interfering with TV broadcasts. This assertion is controversial, however.

white-hat hacker: see hacker.

whitelist: a list of approved email addresses from which a user will accept messages (the opposite of a blacklist). When a mail server configured to use a whitelist receives a message from an unapproved address, the server usually asks the user whether to accept or reject the message. If the user accepts the message, he or she can add the new address to the whitelist, ensuring that future messages from that address are accepted. A whitelist may also be a list of websites from which a web browser will accept content.

white space or whitespace: unused die space in a chip design. (Also used to describe unused radio-frequency spectrum; see White-Fi.) Sometimes a chip layout leaves some space on the silicon die unused because no logic circuitry will fit there, or it will be too far away from other circuitry to work properly. Chip architects often try to fill the otherwise wasted space with additional on-chip memory, such as cache memory.

Wi-Fi: wireless-fixed networking, as in a wireless LAN. The IEEE 802.11 standards are also known as Wi-Fi (sometimes spelled WiFi). Wi-Fi is "fixed" because the wireless clients aren't designed to roam while in use, as cell phones do. Wi-Fi is sometimes misinterpreted as "wireless fidelity." See LAN, WLAN, 802.11.

Wi-Fi Standards

Wi-Fi 7
Wi-Fi 6E
Wi-Fi 6
Wi-Fi 5*
Wi-Fi 4
Wi-Fi 3
Wi-Fi 1
IEEE Designation
2024 (est)
RF Bands
Spectrum (max)
Channel Widths
Throughput (max)
Air Interface
Modulation (max)
MIMO Streams
Up to 16 up/down
Up to 8 up/down
Up to 8 up/down
Up to 8 down
Up to 4 down
Up to 16 users up/down (CMU-MIMO)
28 users up/down
28 users up/down
24 users down
Packet Fragments
Target Wake Time?
Spatial Freq Reuse?
The Wi-Fi Alliance has retroactively branded the standards preceding Wi-Fi 6. This table omits Wi-Fi 2 (802.11a), which operates exclusively in the 5GHz band but was unpopular. Some specifications vary according to government regulations in different regions. *Wi-Fi 5 includes the original Wave 1 (2013) and enhanced Wave 2 (2016) features; †per-stream throughput x MIMO streams. (Source: The Linley Group)

wiki: "What I know is...." Originally, wiki was a brief way to introduce a message or opinion posted online. Now it often describes a wiki page—a web page on which visitors can post remarks and/or edit text on the page. Some wikis are collaborative-work tools or community projects, such as Wikipedia, an online encyclopedia that allows anyone to contribute information or edit previously posted entries. See weblog.

Windows: brand name for a family of Microsoft operating systems. The company began working on Windows in the early 1980s after Microsoft founder Bill Gates saw a prototype of the Apple Macintosh, but Windows 1.0 wasn't released until 1985, two years after it was announced and one year after the Mac's debut. The first few releases of Windows weren't very useful or popular, but that changed in 1995 with the release of Windows 95. Later versions in the same line were Windows 98, Windows 98 SE (Second Edition), and Windows 98 ME (Millennium Edition).

Another version, Windows NT, was based on a rewritten kernel that was more stable. (Before Microsoft's famous split with IBM in the late 1980s, Windows NT was known for a while as OS/2 NT.) Windows NT later became the foundation for Windows 2000, Windows XP Home, and Windows XP Professional. In 2005, Microsoft introduced a version of Windows XP for the 64-bit x86 architecture. In 2007, Microsoft released Windows Vista, a major step from Windows XP. Widely derided for its bloat and poor performance, Vista was replaced by Windows 7 in 2009.

In 2012, Microsoft released Windows 8, which introduced a controversial user interface designed primarily for smartphones and tablet computers with touch screens. Responding to widespread criticism, Microsoft released the slightly improved Windows 8.1 in 2013. Critics were unimpressed, so in July 2015, Microsoft released Windows 10, which was better received. (For technical reasons, there was no Windows 9.) Although Microsoft had hinted that Windows 10 might be a permanent version receiving periodic updates, Windows 11 appeared in late 2021 with yet another revamped user interface and much stricter hardware requirements that greatly limit its compatibility with existing PCs.

Windows CE was another product line in the Windows family; it was designed for handheld computers and other non-PC computing devices. Most versions of Windows run on x86-compatible processors; older versions of NT also briefly ran on Alpha, MIPS, and PowerPC processors. Windows CE ran on a variety of embedded processors. An ARM-compatible variation of Windows 8 known as Windows RT debuted in 2012, but it was intended mainly for tablets and wasn't fully compatible with the x86 version; further development has ceased. See kernel, operating system.

windshield warrior: a person who uses a mobile computer and/or communication device to work out of a car instead of an office. See road warrior.

Wireless-G, Wireless G: another term for the 802.11g wireless LAN standard. See 802.11.

WISP: a Wi-Fi ISP (wireless-fixed Internet service provider). WISPs are usually small, local ISPs. See 802.11, ISP, Wi-Fi, WLAN.

WLAN: wireless local-area network. See LAN, 802.11, HomeRF.

WML: wireless markup language. WML is an abbreviated form of HTML that formats content for display on the small screens of wireless communication devices, such as mobile phones, pagers, and PDAs. WML is based on XML and is the underlying standard for WAP.

word: the width of the general-purpose registers and datapaths in a microprocessor. A processor that uses 32-bit words is called a "32-bit processor." The word width is not necessarily the same as the instruction length.

workstation: a powerful and expensive desktop computer used for professional design work or other demanding tasks. Most workstations have RISC processors. Leading vendors include Sun, SGI, and Hewlett-Packard.

World Wide Web (WWW): an international network of servers that transmits pages of hyperlinked text and graphics to client devices using the Internet and the hypertext-transfer protocol (HTTP). Client devices include personal computers, smartphones, and tablets. Web pages are organized into websites. The WWW first went online at 2:56 p.m. Greenwich Mean Time on August 6, 1991. It's only one application hosted by the Internet; others include Usenet newsgroups (discussion boards) and various file-transfer protocols. See Internet, HTTP, newsgroup, FTP.

worm: a malicious program that attacks computers, usually by corrupting data files or by consuming resources such as CPU cycles, memory, storage, or network bandwidth. Worms are self-contained self-replicating programs that can spread to computers through a network. See cracker, drive-by, hacker, malware, Morris Worm, Trojan horse, virus.

WPAN: wireless personal-area network. See PAN.

WSTS: World Semiconductor Trade Statistics, a nonprofit international trade organization. The WSTS "bluebooks" collect audited statistics about sales of chips worldwide.

WWW: see World Wide Web.

WYSIWYG: (pronounced "wizzy-wig") "what you see is what you get." Describes a style of software design in which documents appear on a computer screen as they will appear when printed on paper. WYSIWYG is a benefit of a GUI (graphical user interface). Earlier text-based screens couldn't easily display graphical images and multiple type fonts.

********** X **********

x86: a proprietary microprocessor architecture invented by Intel and adopted by other companies. Most Intel and AMD processors for PCs, servers, and embedded systems implement the x86 architecture. The first x86 chip was the 8086 in 1978. The x86 is considered a CISC (complex instruction-set computing) architecture because of its complex instruction encoding and some math instructions that operate directly on data in main memory instead of in the chip's registers. However, modern x86 processors downplay the most complex instructions and internally convert CISC instructions into RISC-like operations called micro-ops.

XML: eXtensible Markup Language. A metalanguage for designing document markup languages. Markup languages describe the format of a document. An example of an XML-compliant markup language is Genealogical Markup Language (GedML), which defines a file format for family trees. HTML is another example of a markup language that, like XML, was derived from SGML, the king of markup languages. See HTML, SGML, ODF, OOXML.

XP: (1) shorthand for the Microsoft Windows XP operating system; (2) extreme programming. For definition (1) see Windows. Definition (2) describes an approach to computer programming in which two people sit together and collaborate on writing the program code; the goal is to reduce errors and produce clearer code.

XQD: a standard format for flash-memory cards used in digital cameras and other electronic devices. Introduced in 2012, it's considered a replacement for the older CompactFlash standard, although the cards aren't backward compatible with CompactFlash slots. Maximum capacity can be 2GB or more. See flash memory, CompactFlash, SD, SmartMedia.

XR: extended reality. Synonymous with MR (mixed reality), it describes glasses or goggles that can switch between AR (augmented reality) and VR (virtual reality). These devices may superimpose text or images on a real-world view or display a completely artificial view.

********** Y **********

Y2K: Year 2000. Many experts predicted widespread computer failures after midnight on December 31, 1999 when thousands of programs that manipulate years as two-digit numbers (such as "99" for 1999) might confuse 2000 with 1900. A global effort to fix the "Y2K bug" largely succeeded. Except for minor glitches, the apocalyptic predictions failed to come true.

yottabit: 1,024 zettabits, or 2^80 bits. Abbreviated Yb. See bit, byte.

yottabyte: 1,024 zettabytes, or 2^80 bytes. Abbreviated Y, YB, or yB. See bit, byte.

********** Z **********

Z-buffer: a region of memory that holds numbers representing the depth position of objects in simulated 3D space. It allows an object to eclipse other objects "behind" it.

zero day: the first day that new malware "goes wild" on the Internet, without advance warning. Also known as a "zero-day virus" or "zero-day exploit," etc. Zero-day threats are considered the most dangerous because they give antivirus companies and network administrators no time to update their software to defend against them. See virus, malware, worm.

zettabit: 1,024 exabits, or 2^70 bits. Abbreviated Zb. See bit, byte.

zettabyte: 1,024 exabytes, or 2^70 bytes. Abbreviated Z, ZB, or zB. See bit, byte.

ZIF: zero insertion force. It usually describes a chip socket that allows a chip to drop into place without forcing the pins into holes (and possibly bending or breaking the pins). The ZIF socket may have a lever that locks the chip in place.

ZigBee: an extension of the IEEE 802.15.4 PAN standard for wireless networking. ZigBee (named after the ZigBee Principle, which describes the zigzag dance by which honeybees communicate) is a packet-based standard like Ethernet intended for low data rates (20-250Kbps) and low power consumption. It is suitable for a range of industrial and consumer applications, such as wireless light switches and remote controllers. ZigBee may fill applications for which another PAN standard, Bluetooth, has been too costly. See Bluetooth, Ethernet, PAN, packet.

ZIP: a popular file-compression format. Created in 1989 by Phil Katz, the ZIP format is a single-file archive that may contain one or more compressed files and directories. The compressed files may be of any type (i.e., text documents, spreadsheets, slide presentations, photos, audio, etc). Decompressing the ZIP archive re-creates the original files and directory structure. ZIP archives are useful for reducing the size of email attachments, for downloading software installers, and for saving space when archiving files. See zip bomb.

zip bomb: a malicious compressed file that expands to huge dimensions, sometimes overwhelming the computer's file system or disk drive. Intended to cause trouble, the file is usually disguised as something innocuous, such as music, video, or a document. "Zip" refers to a popular data-compression format (see ZIP), although a booby-trapped file may use any compression format.

Zip drive: a now-obsolete proprietary data-recording device for computers. Created and licensed by Iomega, Zip drives used removable hard disks or cartridges, which had a magnetic recording surface on a fast-spinning metal platter. The Zip drive recorded information (programs and data) on the disk. The first Zip drives stored 100MB or 250MB per disk; later drives stored 750MB. Zip drives were popular in the 1990s but have been replaced by removable flash-memory drives that plug into a USB port. Not to be confused with the ZIP file-compression format, which is unrelated. See flash memory, USB.

zombie: a computer secretly commandeered by a malicious hacker for the purpose of attacking another computer or network. The hacker usually plants a program on the zombie computer that barrages the target with packets—all without the user of the zombie suspecting a thing. Dozens or even hundreds of innocent computers may be transformed into zombies to overwhelm the target. See bot, botnet, DDoS, DoS, packet storm.

zoo virus: a computer virus that exists only in an antivirus-software lab or the creator's own computer. Usually, a programmer creates a zoo virus to prove the existence of a particular vulnerability, then keeps the virus captive to devise a solution. Viruses that escape captivity are said to be "in the wild." See virus, worm, hacker.

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