A/UX: A/UX is Apple’s implementation of AT&T UNIX System V for the Macintosh System 7 launched in early 1988. A/UX 1.1 was released in January 1989, which provided X Window support. A/UX Version 2.0 was released in March 1990 for the Macintosh II and Macintosh SE/30. Apple released A/UX Version 3.0 in late 1991 and discontinued the product in 1995 with Version 3.1.1.
access security: In general, access security is any means to ensure that only authorized persons and devices can access data or systems. In the 1980’s access security was sometimes a feature of security modems that prevented unauthorized access via passwords and callback. The user calling into the modem enters a password, and the modem then confirms the identity and calls back to make a connection.
Today, access security is associated with identity and access management (IAM) tools, which employ multiple authentication methods including passwords, behavioral and device analytics, multi-factor authentication, and biometrics.
AC adapter: An AC (for “alternating current”) adapter is an external power supply for electronic devices that plugs into a wall outlet. They convert the AC coming from the outlet to DC (direct current), which the device requires. AC adapters are also called power adapters, plug-in pack, or simply a brick. The latter term is from earlier days when laptops and microcomputers used larger, brick-sized AC adapters.
acoustic coupler: Sometimes referred to as an acoustic modem, an acoustic coupler is a data communications device that uses the telephone’s audio to send and receive information. “Coupler” refers to how the device connects to the phone, where the phone’s headset is placed on two cups on the device.
active matrix: A type of liquid crystal display (LCD) where a matrix of thin-film transistors (TFTs) control each pixel. This provides more consistent brightness and color, and since it can change a pixel’s state much faster, it can present animation and fast-moving graphics more clearly with less ghosting.
adaptive differential pulse code modulation (ADPCM): Originally developed for speech coding in 1973 by Bell Labs, ADPCM is a technique to convert analog signals (e.g., voice over the phone) to digital. In the process, it lowers the data bandwidth required. ADPCM is used in voice-over-IP communications. In the early 1990s, the Interactive Multimedia Association used ADPCM to develop an audio codec.
ADB (Apple Desktop Bus): An interface used on most Apple Macintoshes and NeXT systems to connect low-speed devices such as the keyboard and mouse. The Apple IIGS in 1986 was the first Apple product to use the ADB, which was developed by Steve Wozniak.
ADC (analog-to-digital converter): A device that converts analog signals to digital signals. ADC input/output (I/O) boards were common add-ons in the early days of microcomputers. Hobbyists and businesses used them to interface computers with devices or machinery that output analog signals—for example, a microphone or instrumentation used to measure.
ADPCM: See “adaptive differential pulse code modulation.”
Advanced Technology Attachment (ATA): An interface standard, approved in May 1994 but developed by Western Digital in 1986, to connect hard drives, CD-ROM drives, and other storage devices to computers. The original ATA specification became known as Parallel Advanced Technology Attachment (PATA) in 2003 when the Serial Advanced Technology Attachment (SATA) specification was introduced. ATA evolved from Western Digital’s earlier Integrated Drive Electronics (IDE) interface.
adware: A shortened form of “advertising-supported software,” adware originally referred to legitimate promotional material included on digital media, primarily a CD-ROM, by the publisher. Today, the term represents a form of malware that serves unwanted ads over the web, sometimes delivering other, more malicious malware.
AI: See “artificial intelligence”
algorithm: In a computing context, an algorithm is a set of instructions designed to solve a problem or calculate a result.
all-in-one: A computer that integrates the main computing unit, keyboard, and video in one enclosure. The Radio Shack TRS-80 Model III, for example, is an all-in-one system. The term is also sometimes used to refer to software suites with a common user interface.
ALOHAnet (a.k.a. ALOHA System or ALOHA): An early computer network developed by Norman Abramson at the University of Hawaii. Operational in June 1971, ALOHAnet was the first demonstration of a public wireless packet data network.
American Standard Code for Information Interchange: See “ASCII.”
analog: Data that consists of continuously variable physical qualities such as sound, spatial position, or voltage.
animation cel: High-resolution, full-color images that can be animated, scaled, rotated, and changed in other ways.
anti-aliasing: A technique used to smooth bit-mapped graphics by removing jagged edges. It’s a common, long-time technique used to improve the look of video games.
API: See “application programming interface.”
APL (A Programming Language): A general-purpose, high-level language that Kenneth Iverson at IBM developed in the 1960s. APL had its own character set that included symbols representing functions and operators. IBM made APL available for several mainframe systems, including the 360/370 and 1130. It was also the embedded language for IBM’s first microcomputer, the 5100.
Apple DOS: Apple’s disk operating system for the Apple II line from 1978 to 1983, when ProDOS replaced it. Typically referred to as simply DOS, the first commercial version was DOS 3.1. Two more versions, DOS 3.2 and 3.3, appeared in 1979 and 1980, respectively.
AppleTalk: Released in April 1985, AppleTalk was Apple’s “personal network” designed to connect up to 32 Macintosh computers. An AppleTalk PC Card would later enable PC compatibles to join the network, and the Apple IIGS was eventually supported as well. Apple dropped support of AppleTalk in 2009.
application: A program or group of programs that provide a specific function to a user on a computer or other device. Small, simple applications might be called “applets” or just “apps,” although the latter is often used for applications of all types today.
application programming interface (API): The API is a set of tools and protocols that allows developers to more easily customize and maintain an application or integrate it with other applications, operating systems, databases, or web-based systems.
application specific integrated circuit (ASIC): A type of chip designed for a specific purpose. Computer designers sometimes combined the capabilities of several standard chips into one ASIC to reduce cost and save space. Some early microcomputers were built from a set of ASICs rather than a single CPU.
A Programming Language: See “APL.”
archival storage: In a computing context, any digital medium used to record and store data that is no longer needed on a regular basis, but must be kept for business or legal reasons. An archival storage medium must be able to maintain the integrity of the data over a long period of time. Historically, magnetic tape has been the most common form of archival storage, but CD-ROM and removable hard drives have been used as well.
ARPANET (Advanced Research Projects Agency Network): When ARPANET went live in 1969, it was the world’s first distributed communications network—the forerunner to the internet. It was also the first packet switching network to use TCP/IP. Funded by the U.S. Department of Defense, ARPANET was developed by a team of business, academic, and government researchers including Vint Cerf, Douglas Englebart, Frank Heart, Robert Kahn, Lawrence Roberts, and Robert Taylor.
artificial intelligence (AI): Definitions for AI vary depending on the school of thought or what a vendor is trying to sell. In the broadest sense, AI is a computer system that can perform a task that had required a human. For modern AI to be successful, it must use algorithms designed to analyze large volumes of relevant data to gain “insight,” which in turn it uses to make a decision or recommend an action. For example, some AI programs analyze network data in search of anomalous activity that might indicate the presence of a hacker. The program will then take action, such as blocking an IP address or sending an alert.
ASCII (American Standard Code for Information Interchange): ASCII provides a character encoding standard to convert keyboard and control characters to electronic data. The ASCII code for a lowercase “j”, for example, is 006A.
ASCII terminal: Any input/output device that can receive ASCII data.
assembler: A program that converts assembly language to the base machine code of the processor.
assembly language: A programming language tightly tied to a CPU’s internal codes.
ASIC: See “application specific integrated circuit.”
asynchronous data communications: The transmission of data over a telecommunications network intermittently rather than in a steady stream. This means that the data segments might be received in a different order than they were sent. The segments are reordered using encoded symbols within the communications.
ATA: See “AT Attachment.”
AT bus: The 16-bit version of the ISA bus used on the IBM PC AT and compatibles, which often provided both 8- and 16-bit bus slots.
audio CD: A compact disc designed to play only audio, although some have limited graphics capability.
audit trail: In computing, an audit trail is the electronic or paper logs used to track activity such as when someone logs into a system or who accesses certain data. Those logs can also help IT administrators troubleshoot technical problems.
authoring software: Software that lets you pull different elements together—text, graphics, video, audio—into an integrated multimedia application. Authoring software became popular in the early 1990s with the rise of multimedia PCs and CD-ROM, and then adapted for the web.
auxiliary data: Checksum data stored in each Mode 1 sector of a CD-ROM that the error detection code/error correction code (EDC/ECC) uses to locate and repair errors.
bandwidth: The capacity of a bus, a network, or internet connection to carry data.
baseband: The frequency range of a transmitted signal before it is converted to a different range. This conversion, or modulation, occurs during cell phone and satellite communications and other telecommunications types. Dial-up modems modulate and demodulate (hence the term ”modem”) signals when they sent and received, respectively.
BASIC (Beginner’s All-purpose Symbolic Instruction Code): An easy-to-learn programming language commonly installed on microcomputers as standard. Developed at Dartmouth in 1964 by John Kemeny and Thomas Kurtz, BASIC comes in many varieties, and vendors sometimes created their own versions to bundle with their computers. Microsoft’s BASIC is sometimes referred to as MBASIC, and the BASIC frequently bundled with MS-DOS is called GW-BASIC.
Even before the PC, BASIC was the popular choice for a programming language on early microcomputers from the MITS Altair to the TRS-80.
basic input/output system (BIOS): Code imbedded in every MS-DOS/Windows PC that tells it how to handle various system components.
battery pack: A self-contained power source usually used in portable computers. Unlike household batteries, most battery packs are often designed for specific models and are not interchangeable with other types of computers, although some battery packs were wrapped bundles of standard C or D-cell batteries. Other common battery types used are alkaline (most notably the original Macintosh Portable), nickel cadmium (NiCad), nickel metal hydride (NiMH), and lithium ion (Li-ion). Li-ion is the most common type used today.
Beginner’s All-purpose Symbolic Instruction Code: See “BASIC.”
benchmark: Any baseline performance measurement, whether its CPU speed, data transfer rates, or data load times.
binary 0 and binary 1: Binary 0 represents a “no transmission” state during a read of a CD-ROM, and binary 1 indicates that a transmission has occurred during a read of a CD-ROM.
BIOS: See “basic input/output system (BIOS)
birefringence: The refraction of light in two slightly different directions, creating two rays. Birefringence can be a problem with optical media like CD-ROM and DVDs when the plastic substrate becomes stressed.
bit: A binary digit, the basic unit of data. Eight bits equals a byte.
bit block transfer (bitblt): A method of copying graphics from one location to another on a video screen.
bits per second (bps): A measure of data transmission speed: the number of bits sent or received per second.
block error rate (BLER): The number of disc read errors that occur per second on a CD-ROM or CD-I drive.
Boolean logic: A method used to formulate search terms to locate and retrieve information from a database, the internet, or other source. Boolean logic uses the operators AND, NOT, and OR to form relationships among keywords, thereby narrowing the parameters of the search. The term gets its name from George Boole, who developed the concept in 1847.
boot: A computer’s startup process to load the operating system and files/preset configurations needed for use.
boot disk: A removable medium used to load and run an operating system or utility. A boot disk originally referred to a floppy disk, but now can be a USB device, external hard drive, or other storage device separate from the computer.
bps: See “bits per second.”
bridge: A network device that connects two similar networks.
bridge disc: A type of CD-ROM disc that works with more than one format standard.
broadband: The wide bandwidth transmission of data that sends multiple signals and data types over a telecommunications network.
bubble memory: A type of non-volatile computer memory developed in the late 1960s, early 1970s and saw some commercial use in the late 1970s and 1980s. It uses a thin film of material that holds small magnetized areas, called bubbles or domains, that store a single bit. Bubble memory at first seemed to offer a promise of greater memory density, but RAM technologies developed more quickly and made bubble memory obsolete by the end of the 1980s. It was developed by Andrew Bobeck at Bell Labs.
buffer: A temporary storage area in physical memory to keep place data while it is being moved. For example, on a CD-ROM drive, the buffer is a 64Kb to 256Kb area of memory that temporarily stores data read off the disc that the computer is not yet ready for.
bump height: On a CD-ROM or CD-I disc, the bump height is the depth of the pits that have been burned into the disc.
bus: The connection between a computers components and its CPU and memory. Many computers have internal or external open bus slots that are used to expand the system’s capabilities through add-on hardware. Some computers use proprietary buses, while others take advantage of standardized bus architectures.
bus mastering: The taking control of a process or task from the computer’s main processor through the system bus. Bus mastering controllers, including many caching controllers used with CD-ROM and other drives, usually have their own processor.
byte: Eight bits–a common unit of measure for electronic data.
C: Created by Dennis Ritchie at Bell Labs in 1972 and 1973, C is a procedural, structured programming language. It became a popular choice for commercial software development in the 1980s and 1990s, and variants such as C++ are still commonly used today.
cache: A storage area in memory or a storage device such as a hard drive that holds frequently accessed data for faster display (e.g., a website) or processing.
cache memory: Fast static random-access memory (SRAM) that a computer’s CPU can access more quickly than regular RAM. It is used to speed processing time.
caching: The use of high-speed memory to hold data read from a storage device until the computer is ready to use it.
caddy: The removable case used by some CD-ROM drives to hold a disc while it is being read.
card frame: A metal frame or cage with bus slots used for system expansion.
carrier-sense multiple access (CSMA): A media access control (MAC) protocol that allows a network node to verify no traffic before transmitting data on a shared transmission medium.
cassette recorder: A standard audio cassette recorder configured for use as a computer storage device.
cathode ray tube (CRT): A now obsolete video display that was the standard monitor technology for use with microcomputers and PCs. A CRT display employs an electron gun to excite phosphers on a glass screen.
CD: See “compact disc.”
CD+G: See “compact disc plus graphics.”
CD-I: See “Compact Disc-Interactive.”
CD-I Bridge: Part of the White Book standard that defines how CD-I data is recorded on CD-ROM XA discs.
CD-I Ready: A bridge format between the audio CD (Red Book) and CD-I standards.
CD-quality audio: Sound produced at a sampling rate of 44.1KHz.
CD-R: See “Compact Disc Recordable.”
CD-ROM: See “Compact Disc Read-Only Memory.”
CD-ROM XA: See “Compact Disc Read-Only Memory Extended Architecture.”
CD-WO: See “Compact Disc Recordable.”
central processing unit (CPU): The main chip that powers a computer. CPUs are classified in part by the number of bits that it can process at one time. Some CPUs can process more bits at a time internally, but fewer through its external data bus. Specific CPUs are shown in the table below:
| CPU | Manufacturer | Type | Notes |
| 2901 | AMD | 8-bit | |
| 6502 | MOS Technology | 8-bit | Faster versions had letter suffixes, e.g., 6502A. |
| 65C02 | MOS Technology | 8-bit | CMOS version of the 6502 |
| 6800 | Motorola | 8-bit | |
| 6809 | Motorola | 8-bit | |
| 8080 | Intel | 8-bit | |
| 8085 | Intel | ||
| 8086 | Intel | 16-bit | |
| 8088 | Intel | 16-bit | |
| 32016 | National Semiconductor | 32/16-bit | |
| 68000 | Motorola | 32/16-bit | Subsequent, faster versions were labeled 68010, 68020, 68030, and 68040 |
| 80186 | Intel | 16-bit | |
| 80286 | Intel | 16-bit | |
| 80386 | Intel | 16-bit | |
| ARM 2 | Acorn | 32-bit | RISC-based processor |
| D780C | NEC | 8-bit | Z80 equivalent |
| MN1613 | Fujitsu | 16-bit | |
| NSC-800 | National Semiconductor | 8-bit | low-power Z80 equivalent |
| Z80 | Zilog | 8-bit | Faster versions had letter suffixes, e.g., Z80A |
| WD16 | Western Digital | 16-bit | |
CGA: See “Color Graphics Adapter.”
channel bit: The bits formed by the conversion of 8-bit bytes to 14-bit bytes.
checksum: A number generated by a special algorithm that is used to ensure data integrity.
CIRC: See “cross-interleave Reed-Solomon code.”
circular buffer read-ahead: A technique used to read data continuously into a CD-ROM drive’s buffer, thereby keeping the buffer full and speeding throughput.
client: On a network, any attached device that serves as an endpoint.
client-server computing: Extends distributed process to the desktop by splitting an application into a front-end client application that resides on a user’s workstation and a back end that runs on computing resources anywhere on the corporate network. The client application presents and manipulates data on the workstation. The server processes, stores, and protects the data.
CLV: See “constant linear velocity.”
CMIP: See “Common Management Information Protocol.”
CMOS: See “Complementary Metal Oxide Semiconductor.”
CMOT: See “Common Management Information Protocol.”
coaxial cable: A cable with a conductor at its center with a tubular insulating layer. Also called coax. Coax is used as a low-loss transmission line for broadband internet, high-speed computer data buses, and other applications.
collision detection: The detection of when two or more objects intersect. Collision detection is used in the development of video games and simulations as well as robotics and self-driving vehicles.
Color Graphics Adapter (CGA): A video mode that was commonly used on PCs that provides 320- by 200-dot resolution. IBM developed it in 1981 and sold a CGA card for its PC to provide color graphics.
command: An instruction for a computer to execute a specific task, such as “print” or “goto.”
command syntax: The rules for composing a series of commands on a computer.
Common Management Information Protocol (CMIP): A network management protocol defined by the X.700 recommendations of the ITU Telecommunication Standardization Sector (ITU-T). It is the protocol specified by the Open System Interconnection (OSI) network management model. CMIP can also be used over TCP/IP and is referred to as CMOT.
communications software: This is a general term that has evolved over time. Broadly, communications software allows people or devices to communicate and exchange data over the cloud or a network. Originally, communications software was used with modems to connect with other modems or online services.
compact disc (CD): An optical storage medium and format developed by Sony and Philips, originally to store and play audio only. It was released in 1982.
compact disc plus graphics (CD+G): The part of the Red Book audio CD specification that allows the incorporation of limited graphics.
Compact Disc-Interactive (CD-I): A CD format developed by Philips that better enables the playback of multimedia, interactive software. Released in 1990, CD-I is defined by the Green Book specification.
Compact Disc Read-Only Memory (CD-ROM): A 4.72-inch diameter plastic and aluminum disc designed to optically store audio, text, video, and graphics data. See also “Yellow Book” and “Compact Disc Read-Only Memory Extended Architecture (CD-ROM XA).”
Compact Disc Read-Only Memory Extended Architecture (CD-ROM XA): An enhanced CD-ROM format standard that allows for multimedia playback and better synchronization of multimedia data types.
Compact Disc Recordable (CD-R): A recordable compact disc. It uses a gold reflective surface rather than aluminum and adds a dye-based layer to enable the recording of data. Also referred to as CD-WO (compact disc write-once).
Complementary Metal Oxide Semiconductor (CMSO): A type of semiconductor that requires less power. CMOS-based processors are commonly used in battery-powered computers for that reason.
comparator: The circuitry in a CD-ROM drive that measures the outputs produced by the laser focusing circuitry.
composite: A single video signal that contains information for chroma, luminance, and sync. A composite monitor is capable of decoding a composite signal.
computer trainer: Typically a bare single-board computer with a hexadecimal keyboard and calculator-like readout designed to teach the internals of a given CPU or system design. Trainers were most common in the 1970s.
condenser lens: A lens that increases the intensity of the laser light in CD-R drives.
configuration: From a hardware perspective, configuration refers to a system’s or network’s arrangement of components and the hardware, software and firmware used. From a software perspective, configuration refers to choices made for pre-programmed settings.
constant linear velocity (CLV): The data on a compact disc or other optical media is stored in one long spiral track. A drive must maintain a constant speed (linear velocity) as it scans the track. Therefore, the disc must spin slower to read the inner tracks and faster to read the outer tracks.
consumer electronics: A broad category of electronics for everyday personal use, such as a TV or smartphone. Consumer electronics might be used for entertainment, communications, lifestyle, or home office applications.
controller: A device, usually an add-in card in older systems, that controls a specific device or component of a computer. A SCSI controller is often referred to as a host adapter.
Control Program for Microcomputers (CP/M): The dominant microcomputer operating system before MS-DOS, developed by Digital Research. Many versions of CP/M were available, including CP/M-86 for 16-bit Intel-based systems and the multitasking Concurrent CP/M. System vendors often licensed CP/M to create their own versions of the operating system.
coprocessor: A second or third CPU that works either in parallel to or in conjunction with the main CPU.
CP/M: See “Control Program for Microcomputers.”
CPU: See “central processing unit.”
cross-coding: An error-detection and correction algorithm used to generate checksums.
cross-interleaved Reed-Solomon code (CIRC): Error correction code developed specifically for CD-ROM.
cross-platform development: The act of developing one application for more than one platform, or the conversion of an application from one platform to another.
CRT: See “cathode ray tube.”
CSMA: See “carrier-sense multiple access.”
DAC: See “digital-to-analog converter.”
daisy-chain: The act of connecting multiple devices using one host adapter or controller.
database: A structured or unstructured collection of data that is stored and accessed from a computer, server, internet, or the cloud.
data integrity: The assurance of the accuracy and consistency of stored and processed data.
data interchange format (DIF): A text file format that enables the import and export of spreadsheet files among different spreadsheet programs.
data replication: The copying of important information from one server to other servers on the network.
dB: See “decibel.”
decibel (dB): a measure of the amplitude or intensity of sound.
density: In terms of storage media, density refers to the amount of data that can be placed in a given area of the media.
device driver: Software that tells a computer’s operating system how to communicate with a peripheral such as a printer, CD-ROM drive, or scanner.
DIF: See “data interchange format”
digital signal processor (DSP): A specialized processor for one task such as video or audio. A DSP takes processing load off the main system CPU.
digital-to-analog converter (DAC): A device that converts digital signals to analog signals.
Digital Video Interative (DVI): Introduced by Intel in 1987, DVI was the first multimedia video standard for PC-compatibles. Built around a compression chipset, the standard incudes a file format, a digital container format, and video and audio compression formats.
digitize: The act of converting images, sound, text, and other types of data to a binary numerical form understandable by a computer.
direct memory access (DMA): A technique for moving data directly between main memory and a peripheral.
directory: A hierarchical file system catalog structure.
disk or diskette: See “floppy disk.”
disk format: Each type of hard drive, floppy disk, USB device, or solid state drive must be formatted so that it is partitioned and set up with a file system that is compatible with the operating system.
disk I/O: The read/write operations of any physical disk drive.
diskless workstation: A stripped down computer used as a network terminal with no internal storage.
disk mirroring: The replication of logical disk volumes to another physical drive in real time to ensure data availability.
disk operating system (DOS): The generic term for an operating system designed for disk-based systems. Some vendors, however, unimaginatively used “DOS” as their product name.
display: Any video output device that visually presents information in human-understandable form.
distributed application: Software designed to run on multiple devices connected to a network.
DMA: See “direct memory access.”
docking station: An expansion unit for portable computers that provides additional storage, I/O ports, or slots for add-in cards.
DOS: See “disk operating system”
dot pitch: The measurement used to indicate the proximity of pixels to one another on a video display.
double-speed CD-ROM drive: A drive that reads data at 300Kbps, twice the single-speed rate.
drive: The basic storage hardware unit that reads/writes data. Examples include floppy, CD-ROM, CD-I, hard, Winchester, and solid state drives.
DSP: See “digital signal processor.”
DVI: See “Digital Video Interactive.”
dye-recording layer: A chemical layer found in CD-R discs that reacts with the recording laser to form the pits that represent data.
Dynabook: A Xerox PARC project to design a book-sized computer, proposed by Alan Kay.
ebook: An “electronic book” is a print book that has been converted to a digital medium such as CD-ROM, or a book that has been created for digital publication.
Ecma International: See “European Computer Manufacturers Association.”
EDC/ECC: See “error detection code/error correction code.”
editor: A software tool that allows you to modify individual elements. Examples include text editors, audio editors, and image editors.
EGA: See “Enhanced Graphics Adapter.”
eight-to-fourteen modulation (EFM): The process of converting 8-bit bytes to 14-bit bytes.
EISA: See “Extended Industry Standard Architecture.”
email: “Electronic mail” is the digital transmission of messages to one or more recipients. Invented in the 1960s by Ray Tomlinson, email was not used commercially until the 1970s.
EMS: See “Expanded Memory Specification.”
emulation: Through emulation, software, a computer, or an electronic device that can imitate another program or device. Software that enables emulation is called an emulator, and emulators are commonly used to allow older video games to run on modern computers.
encryption: The cryptographic encoding of data for security reasons. The data is decoded using a decryption key.
Enhanced Graphics Adapter (EGA): An IBM graphics standard for PCs that supports 640 x 350 graphics and 16 colors. Released in 1984, it superseded CGA.
error detection code/error correction code (EDC/ECC): The software that resides within firmware that identifies and corrects read errors from a CD-ROM disc or other storage media.
EPROM: See “erasable programmable read-only memory.”
erasable programmable read-only memory (EPROM): A memory chip that retains its contents until exposed to ultraviolet light. New content may be rewritten to the EPROM using an EPROM programmer, also called an EPROM burner.
Ethernet: A network protocol developed in 1973 at Xerox PARC as a means to network Xerox Alto computers. Robert Metcalfe was the principle inventor. It got its name from the 19th Century concept of ether, in which electromagnetic waves can travel. It became a standard in 1980 when Metcalfe brokered an agreement among Intel, Digital Equipment Corp., and Xerox. That resulted in a set of specifications and design information for Ethernet.
Ethernet was further solidified as a standard in 1982 when the IEEE 802 committee and the European Computer Manufacturer Association proposed standards nearly identical to Ethernet.
Eurocard bus: A European bus standard used by Acorn and other vendors. Eurocard’s mechanical specifications were used for the VMEbus.
European Computer Manufacturers Association: A non-profit organization dedicated to creating standards for computer hardware, programming languages, and communications. The organization changed its name to Ecma International in 1994.
Expanded Memory Specification (EMS): A standard technique that allows MS-DOS-based PCs to use more than 1MB of memory. Often referred to as simply “expanded memory.”
expander board: An add-on board that provides additional expansion slots.
Extended Industry Standard Architecture (EISA): An enhanced bus standard for PCs that allows for expansion slots with greater bandwidth. Released in September 1988, EISA was developed by a consortium of nine PC clone vendors known as the “Gang of Nine” to compete with Micro Channel architecture, IBM’s proprietary bus standard.
FAT: See “file allocation table.”
father: The metal die created from the glass master during the compact disc manufacturing process.
file allocation table (FAT): The part of a disk’s file system architecture that keeps track of where all the clusters of a given file are located on the disk. FAT dates back to 1977 and was created for floppy disks, but is still commonly used today.
file attribute: A piece of information or metadata about a particular file, such as a timestamp of when it was recorded.
file format: A given system’s standard method for how it encodes data for storage.
file transfer: The transmission of a digital file from one device to another, either through a communications network or directly device-to-device.
File Transfer Protocol (FTP): A communications protocol used to transfer files across or between networks.
firmware: Software that is hard-coded within a chip on a device. Originally, this was typically done using an EPROM.
floppy disk: A magnetic, removable storage medium encased in a flexible or rigid sleeve that comes in several different physical and logical formats. The most common physical formats are 5.25 inches, 3.5 inches, and 8 inches. Floppy disks may be single- or double-sided (meaning they store data on one or both sides) and single- or double-density. A double-density disk stores twice as much data in the same surface area as a single-density disk.
FMV: See “full-motion video.”
focus coil: Part of a CD-ROM’s focusing mechanism.
focus servo: The motor that adjusts the focus of the laser in a CD-ROM drive.
format: The act of preparing a storage devices such as a floppy drive, flash drive, or hard disk drive for the partitioning the operating system expects. This includes deleting all existing data and setting up a file system.
formatting software: Software used to write and format data to a drive.
forward sense diode: A diode found in CD-R drives that measures the intensity of laser light.
fragmentation: The phenomenon where file clusters become widely dispersed on a hard disk or other storage media because frequent reads and writes have limited the number of contiguous free space.
frame: A single image within a video sequence.
Frankfurt Group: An industry consortium that devised a CD-ROM file format standard to replace ISO 9660. It became ISO 13490.
frequency response: The range of sound a computer’s sound board can generate.
front panel: Contains the control switches, LEDs, and associated circuits found on early micros.
FTP: See “File Transfer Protocol.”
full-motion video (FMV): The ability to play video sequences at 30 frames per second.
game paddles: Controllers that typically use dials and buttons for game play.
game port: An external connection for joysticks, game paddles, and other types of controller/pointing devices.
gas plasma display: A thin-panel display that uses neon gas sandwiched between two plates coated with a conductive print. Passing a current through a single point on the plate lights the area beneath it.
gateway: A network device that allows the transmission of data from one network to another.
GB: See “gigabyte.”
GEM: See “Graphics Environment Manager.”
General Purpose Interface Bus (GPIB): See “IEEE-488.”
ghosting: The effect seen when a moving image on a video screen leaves a “trail.” This trail is the result of the persistence of the phosphers on a CRT display or LCD crystals that fade rather than immediately turn off.
gigabyte (GB): 1,024 megabytes.
glass master: A glass disc used in the compact disc manufacturing process to create a die to stamp out copies.
GPIB: See “IEEE-488.”
graphical user interface (GUI): A software-generated shell or abstraction between the user and the operating system or an application that makes it easier to use through the use of graphic icons and other visual aids.
graphics: The display of or ability to display images on a computer.
Graphics Environment Manager (GEM): A graphical user interface developed by Digital Research in 1985 and sometimes used with CP/M, MS-DOS, and other operating systems.
Green Book: The CD-I format standard established by Philips.
GUI: See “graphical user interface.”
hard disk drive (HDD): An enclosed, rigid, electro-mechanical, high-capacity storage device. Also called a fixed disk, it uses magnetic, spinning platters and a read/write mechanism to record and retrieve data.
hardware: Generally refers to any physical components of a computer system.
hardware handshaking: The communication between two devices or systems through the use of a common protocol.
HDD: See “hard disk drive.”
header bytes: The bytes within each sector on a CD-ROM drive that provide address and mode information.
Hewlett-Packard Interface Bus (HP-IB): see “IEEE-488.”
HFS: See “Hierarchical File System.”
hierarchical directory tree: A file structure that uses a root directory with one or more levels of subdirectories.
Hierarchical File System (HFS): The Mac OS file system used by the Macintosh computer originally for floppy and hard disks, but later for other media such as CD-ROMs. “Hierarchical file system” is also a generic term used to describe any file system that presents files in a hierarchy.
High Sierra: The unofficial CD-ROM file format standard that was eventually modified and accepted as ISO 9660.
hit rate: The rate at which the computer finds information it requires in cache memory and not on the storage device.
home computer: A low-cost, single-user computer designed for use in the home.
host: A network-connected device or computer that provides resources or services to the network or users.
host adapter: A type of controller.
hybrid disc: A CD-ROM that uses more than one type of file format.
Hybrid Disc Standard: The format standard on which Kodak’s Photo CD is based.
hypertext: On-screen data that is linked to other, related data, such as a link in a web article to another web page.
IC: See “integrated circuit.”
IDE: See “Integrated Drive Electronics.”
IEEE: See “Institute of Electrical and Electronic Engineers.”
IEEE-488: A bus standard developed by Hewlett-Packard as the HP-IB (Hewlett-Packard Interface Bus) and adopted as the IEEE-488 standard. It is also referred to as the GPIB (General Purpose Interface Bus).
IEEE-802: A set of local area network (LAN) standards that addresses the physical layer specifications of a range of networking technologies including Ethernet and wireless.
independent software vendor (ISV): Any organization that develops or sells software.
Industry Standard Architecture (ISA): The 8-bit bus used in the IBM PC, PC XT, and PC AT.
Integrated Drive Electronics (IDE): A bus standard for connecting a computer to a storage device such as a hard or CD-ROM drive.
interrupt: A specific instruction that tells the computer to stop what it’s doing and run a particular routine.
Institute of Electrical and Electronic Engineers (IEEE): A professional organization for electrical and electronic engineers. It also serves as a standards body.
integrated circuit (IC): A set of electronic circuits mounted on a flat semiconductor material.
intelligent terminal: A terminal connected to a network or mainframe that contains memory and processing capability, as opposed to a dumb terminal that relies entirely on the server or another connected computer.
interactive television (ITV): Television programming that has been modified or created using hardware and software to be interactive with viewers. In the 1990s, this was often done through settop boxes, which might have used a CD-ROM drive. Today, most smart TVs have interactive features built in.
interface: A connection or adapter between the computer and an external device.
International Organization for Standardization (ISO): An international industrial and commerical standards-setting body
internetworking: The connecting of different networks through devices such as routers or gateways.
IRQ: Interrupts used for the COM (communications) ports on Intel-based PCs. COM1 and COM3 usually share IRQ4; COM2 and COM4 usually share IRQ3. You can’t have two devices using the same IRQ at the same time.
ISA: See “Industry Standard Architecture.”
ISO: See “International Organization for Standardization.”
ISO 9660: A file format standard for CD-ROMs established by the International Organization for Standardization. Most types of CD-ROMs use ISO 9660.
ISO 10149: The official ISO designation for the Yellow Book CD-ROM standard.
ISO 13490: See “Frankfurt Group.”
isochronous: Two events that happen at the same time.
ISV: See “independent software vendor.”
ITV: See “interactive television.”
jaggies: The rough edges often found on bit-mapped graphics.
jewel case: The plastic cases used to store CD-ROMs.
Joint Photographic Experts Group (JPEG): A common compression standard for photographic and other images.
joystick: A type of game controller that uses buttons and a lever that moves in all directions.
JPEG: See “Joing Photographic Experts Group.”
jukebox: A term sometimes used to describe a multiple-drive CD-ROM server.
karaoke CD: See “Video CD.”
KB: See “kilobyte”
Kb: See “kilobit”
Kilobit: A unit of measure for computer memory or data. A kilobit equals 1,024 bits.
kilobyte (KB): A unit of measure representing 1,024 bytes of data.
kiosk: A booth-like system, typically set up for public use, that uses a computer and perhaps an internet connection to allow people to perform specific tasks or gather information without human assistance.
LAN: See “local area network.”
land: the flat area between pits on a compact disc track. The transitions between the pits and lands represent data.
laser diode: See “semiconductor diode.”
laser videodisc: A 12-inch ancestor to the compact disc that is used primarily to play back movies.
latency: The time spent retrieving, presenting, or processing data before it is accessible to a user or device.
layered error-correction code (LECC): The scheme by which errors that CIRC cannot correct are processed again by EDC and ECC.
LCD: See “liquid crystal display.”
lead-in area: The place on a CD-R disc where the final table of contents is written.
lead-out area: The place on a CD-R disk that tells the drive that there is no more data to be read.
LECC: See “layered error-correction code.”
LED: See “light-emitting diode.”
light-emitting diode (LED): A low-power light used often used for status displays.
liquid crystal display (LCD): A low-power video display often used in battery-powered devices. LCDs are constructed with a layer of a liquid crystal between two transparent electrodes. An electric current is used to alter the alignment of molecules in a small area and make it opaque and visible.
load balancing: The process of distributing workloads across multiple computing resources and components to avoid bottlenecks and improve performance.
local bus: A system bus that provides a direct connection to the main processor.
local area network (LAN): A network of computers and other devices that’s confined to a specific location.
logical file format: The way in which the directories and files are organized on a storage medium.
logical sector structure: The way in which sectors are organized on a storage medium.
log in: The act of entering credentials for access to a system or service.
Logo: A simple programming language often used for educational purposes.
machine language or code: A low-level language directly understood by the CPU.
Machine Operating System (MOS): Acorn’s operating system for the BBC system.
magneto-optical (MO): A writable and readable optical storage technology.
mainframe: In the days of “big iron,” the mainframe was the primary processing unit of a computer system. When minicomputers and then business-class microcomputers arrived, mainframe became a designation for the most powerful computer category. Today, the term represents large-scale, high performance, high reliability systems.
markup: To insert code into electronic text or design layouts to indicate structure.
MB: See “megabyte.”
Mb: See “megabit.”
MBTF: See “mean time between failure.”
MCI: See “Media Control Interface.”
MDA: See “Monochrome Display Adapter.”
MD Data: A proprietary data format used by Sony’s 3.5-inch MiniDisc player. MD-ROM is the read-only version of the disc.
mean time between failure (MBTF): The expected amount of time a type of hardware unit will operate before it fails.
media clipart: Collections of images, videos, sound clips, and other media elements distributed using a digital medium.
Media Control Interface (MCI): A component of Microsoft Windows that determines which device you play from the Media Player—CD-ROM, sequencers, etc.
medium: In computing, a medium is a type of physical data storage and playback such as a hard drive or CD-ROM.
megabit (Mb): A unit of measure for data storage equaling 1,048,576 bits.
megabyte (MB): A unit of measure for data storage equaling 1,048,576 bytes.
megahertz (MHz): An electronic unit of measure used to determine CPU speed. A megahertz is one million cycles per second.
menu: A set of options for a user to select within an application or operating system environment.
metal-oxide-semiconductor field-effect transistor (MOSFET): An insulated field-effect transistor fabricated using controlled oxidation of a semiconductor.
metering software: Software that keeps track of software or database usage for billing purposes.
MHz: See “megahertz.”
Micro Channel: IBM’s proprietary 16- or 32-bit system bus for some PS/2 systems. Introduced in 1987.
microcomputer: A standalone, relatively inexpensive, single-user computer.
microprocessing unit (MPU): An integrated circuit that contains different core elements of a computing system. Those elements might include a CPU, floating point unit, memory management, or a clock.
microwave: A form of electromagnetic radiation with frequencies between 300MHz and 300GHz.
MIDI: See “Musical Instrument Digital Interface.”
minichanger: A CD-ROM drive with a mechanical assembly that can hold a number of discs and automatically swap among them.
minicomputer: A mid-sized computer not as powerful as a mainframe. Minicomputers are often multiprocessor systems that support many users.
mixed-mode disc: CD-ROMs that have Red Book audio tracks (Mode 2) recorded on them along with CD-ROM (Mode 1) tracks.
MO: See “magneto-optical.”
Mode 1: The CD-ROM recording scheme that incorporates EDC/ECC.
Mode 2: The data-only CD-ROM encoding scheme (Red Book audio).
modulate: To vary or change.
modem: A term derived from “modulator-demodulator.” A modem is a device that converts data to an appropriate format for transmission to another modem, a computer, or a network.
monitor: (1) The computer’s separate video display unit such as a CRT. (2) Software that “monitors” computer activity.
monochrome: Of a single color.
Monochrome Display Adapter (MDA): A monochrome video standard used on PCs and compatibles. It was developed by IBM and released in 1981 with the original PC.
MOS: See “Machine Operating System.”
MOSFET: See “metal-oxide-semiconductor field-effect transistor.”
mother: A metal die created from the father die during the compact disc manufacturing process.
Moving Picture Expert Group (MPEG): A popular compression scheme for video.
MPEG: See “Moving Picture Expert Group.”
MPU: See “microprocessing unit.”
MS-DOS: Microsoft’s PC operating system.
MSX: A home-computer hardware and software standard based on a Z80 CPU and Microsoft BASIC. MSX was more popular in Europe and Asia than in North America. All MSX systems can share software (cassette and ROM cartridge) and peripherals. The MSX-2 standard, released in late 1985, provided support for 3.5-inch floppy drives and 512 x 512 graphics with 256 colors.
Multibus: A computer bus standard developed by Intel for industrial systems. It has been adopted as the IEEE 796 bus.
multifunction card: A computer add-in card that performs more than one function. Many sound boards, for example, also provide a SCSI bus.
multimedia: The presentation of multiple types of media—text, images, video, sound—on a computer or other device.
Multimedia PC (MPC): A recommended standard by the Multimedia PC Marketing Council (a working group of the Software Publishers Association) for configuring a PC with a CD-ROM drive used for multimedia applications. The term “multimedia PC” is also used generically to describe a PC optimized to run multimedia applications.
multiprocessor: Having more than one main processor.
multisession: The ability to record an optical disc in more than one session, or the ability to read a partially recorded disc.
multitasking: The ability for a system to run multiple programs at the same time, where the user may switch among them.
multi-user system: A computer designed to support more than one user simultaneously.
Musical Instrument Digital Interface (MIDI): A standard for connecting synthesizers, sound cards, and other music devices to the computer.
named pipes: An industry standard interface for application-to-application communications.
National Bureau of Standards (NBS): The U.S. government’s measurement and standards laboratory. Founded in 1901, it became the National Institute of Standards and Technology (NIST) in 1988.
National Institute of Standards and Technology (NIST): See “National Bureau of Standards.”
National Television Standard Committee (NTSC): The TV video format standard used in North America. Some early microcomputers were NTSC compatible so they could use a standard TV as a display.
NBS: See “National Bureau of Standards.”
NetBIOS: See “Network Basic Input/Output System.”
NetWare Loadable Module (NLM): Software that adds features to or enhances Novell NetWare.
network: A group of computers connected so they can share data and resources.
network adapter: See “network interface controller.”
network interface controller (NIC): Also called a “network adapter,” a NIC is a hardware component that connects a computer to a network.
Network Basic Input/Output System (NetBIOS): Provides services to the session layer of OSI-based networks to enable applications on separate connected computers to communicate over a network.
network operating system (NOS): An operating system designed to support multiple devices and device types over a network.
NIC: See “network interface controller.”
NIST: See “National Bureau of Standards.”
NOS: See “network operating system.”
NTSC: See “National Television Standard Committee.”
NuBus: The expansion bus used by all Macs from the Mac II to the Performa.
objective lens: The last lens that the laser light travels through before striking the surface of an optical disc.
Object Linking & Embedding (OLE): A component of Microsoft Windows that allows different applications to share data.
OEM: See “original equipment manufacturer.”
office automation: The use of computers, software, and networks to digitally create, collect, process, store, and transmit information. Office automation also can streamline business processes.
OLE: See “Object Linking & Embedding.”
one-third stroke: The accepted method to measure the performance of CD-ROM and other optical drives. It requires that a search take place over at least one-third of the disc surface, not track-to-track.
online data retrieval: The access of remote information using telecommunications.
operating system (OS): The software that coordinates the operation of the hardware components within a computing system or a network.
optical fiber: A thin fiber of glass or plastic that can transmit light over a long distance for the purpose of communications.
optical head: The laser read mechanism in an optical drive.
optical media: Storage media that uses laser light to record and read data.
optical read-only memory (O-ROM): A hybrid media that is part CD-ROM format and part magneto-optical (writable) format. Also called P-ROM (partial ROM).
Orange Book: The format standard for CD-R and MO discs.
original equipment manufacturer (OEM): A company that manufactures a product that is sold to another company, which resells the product under its own brand.
OS: See “operating system.”
P2P network: See “peer-to-peer network.”
packet switching: A method of transmitting data over a network by breaking it up into smaller bits (called packets) and then reassembling them at the receiving end. Packet switching is fast because it minimizes latency.
PAL: See “Phase Alternating Line.”
parallel I/O: The processing of input and output in parallel rather than sequentially.
parallel port: An I/O port found on most microcomputers and PCs to connect external devices such as printers or CD-ROM drives.
parameter: A factor that, with other parameters, defines a system or conditions of operation.
Pascal: A high-level, structured programming language.
passive matrix: A type of LCD that features low cost at the expense of some lost image quality.
passive network: A network where each connected device works on a predefined function or process.
password: A credential known only to the user that grants access to systems, applications, or online services.
PBX: See “private branch exchange.”
PC: See “personal computer.”
PCA: See “program calibration area.”
PC-DOS: IBM’s version of MS-DOS.
PCI bus: “See Peripheral Component Interconnect bus.”
PCM: See “pulse code modulation.”
PCMCIA Standard: See “Personal Computer Memory Card International Association Standard.”
PDA: See “personal digital assistant.”
PDN: See “public data network.”
peer-to-peer (P2P) network: Also called a peer-based network, it is the connection of two or more computers that share resources without going through a server.
peripheral: An external add-on device that add functionality to a computer, such as a printer.
Peripheral Component Interconnect (PCI) bus: A high-speed local bus standard.
personal computer (PC): Although the term “personal computer” has been used to describe any single-user computer, “PC” is heavily associated with the IBM PC and its many clones and compatibles.
Personal Computer Memory Card International Association (PCMCIA) Standard: A bus standard for small, credit-card-sized add-in cards used in portable devices.
personal digital assistant (PDA): A small handheld computer designed for personal information management and communications.
Phase Alternating Line (PAL): A European television standard that some early European microcomputers supported so they could use a TV as a display.
phase transition: A term used to describe transitions in states of matter between solid, liquid, and gas.
pit: A depression in the reflective layer of a compact disc that represent data.
pitch: The distance between tracks on a compact disc.
platform: The hardware and operating system on which an application runs.
player: A self-contained unit to play compact discs. It contains a drive and controlling electronics.
PMA: See “program memory area.”
port: An external connector that usually accepts only one type of device.
power supply: A device that converts AC power to DC and regulates the electrical current going to the computer. External power supplies are often referred to as AC adapters.
premastering software: Software used to prepare data for the proper format to be recorded on CD-ROM.
printer: An output device that prints digital content on paper or another physical surface.
printer management: Software and processes that allow the management and maintenance of multiple printers within an organization.
private branch exchange (PBX): An internal business telephone system that switches calls between an organization’s users on local lines while allowing all users to share external phone lines.
ProDOS: Apple’s more advanced operating system than AppleDOS for the Apple II line.
program: An set of instructions that when executed on a computer performs a task.
program calibration area (PCA): The area on a CD-R disc that the laser reads to calibrate itself to the disc.
programmable read-only memory (PROM): Solid-state storage that can be written to once.
program memory area (PMA): The part of a CD-R disc that contains the track numbers and their starting and stopping addresses.
Project MAC: See “Project on Mathematics and Computation.”
Project on Mathematics and Computation (Project MAC): A collaborative computing project funded by Department of Defense’s Advanced Research Projects Agency (ARPA) and the National Science Foundation and conduced at the Massachusetts Institute of Technology (MIT). Its goal was to enable multiple people to access a single computer from remote locations.
P-ROM: See “O-ROM.”
PROM: See “programmable read-only memory.”
proprietary: Software, hardware, and other technology that is exclusive to a specific vendor.
protocol: A set of rules for transmitting or processing data among multiple devices or networks.
public data network (PDN): A network set up for the purpose of providing data transmission services to the public.
pulse code modulation (PCM): A method of digitizing analog sound. PCM matches samples against a predetermined set of permitted values. It then codes the selected value as a series of pulses representing “on” or “off” (or the binary 0 or 1).
quad-speed drive: A CD-ROM drive that reads data at 600Kbps, four times the single-speed rate.
quantization: Measurement of how much data a sound board can accumulate per sample. A higher sampling rate provides greater accuracy of the sampled sound.
quarter wave plate: The part of a CD-R drive that rotates the beam toward the photodetector.
radio frequency (RF) modulator: A device that allows a standard TV to display video signals from a computer.
RAM: See “random access memory.”
random access: The ability to go directly to and retrieve a discrete piece of data from a storage medium.
random access memory (RAM): Temporary storage hardware in which the computer executes programs.
read-ahead: The ability to access data from a storage medium and place it in a buffer before the computer needs it.
read-only memory (ROM): Permanent solid-state storage that holds system software or user applications.
record locking: A technique to prevent people or programs from accessing the same data in a database at the same time.
Red Book: The digital audio standard, developed by Philips and Sony, for compact discs.
reduced instruction set computer (RISC): A microprocessor with a reduced number of instructions but providing high performance.
reflective layer: The middle part of a compact disc that consists of the aluminum layer containing the data.
refresh rate: The rate at which a video display updates the screen. Also referred to as the “scan rate.”
remote network management: Software that allows network administrators to monitor network endpoints and servers.
remote computer: A computer that a user does not have physical access to, but can connect to through a network, VPN, or other means.
reseller: A sales channel in the technology products industry. A reseller buys hardware, software, and services from the original provider and resells them to businesses or consumers, sometimes providing value-added services.
retail: A direct-to-consumer sales channel for the tech industry.
RF modulator: See “radio frequency modulator.”
RGB (red green blue): A type of video display that accepts red, green, and blue color signals.
RISC: See “reduced instruction set computer.
RiscOS: Acorn’s operating system for its RISC-based computers.
RLL: See “run-length limited.”
Rock Ridge Extensions: CD-ROM file format extensions to ISO 9660 that accommodate the UNIX file structure.
ROM: See “read-only memory.”
router: A hardware device that routes messages from one network to another similar one. A wireless router also serves as a wireless access point.
routing: The selection of a path for traffic within a network or across multiple networks.
RS-232: A serial computer communications standard established by the Electronic Industry Association (EIA). RS-232 stands for “recommended standard number 232.” RS-232C refers to revision C of the original standard. Other EIA serial point-to-point communications standards include RS-422 and RS-423.
RS-422/RS-423: See “RS-232.”
run-length limited (RLL): A line coding technique used to send arbitrary data over a communications channel with limited bandwidth.
runtime: A core piece of executable code that allows you to access or view data created by the fully featured version of the software.
sampling rate: The speed at which a sound board generates sound, measured in frequency.
SAP: See “Service Advertising Protocol.”
scan rate: See “refresh rate.”
scripting language: A high-level software development language where code is written using natural-language-like scripts.
SCSI: See “Small Computer System Interface.”
sector: On some storage media, a sector is the minimum unit of data that a drive can access. On a CD-ROM, a sector is 2352 bytes. Sectors are sometimes referred to as “blocks.”
semiconductor: A material such as silicon that has an electrical conductivity value somewhere between a conductor such as copper and an insulator. Because a semiconductor’s conducting properties can be manipulated, they are used in the production of integrated circuits.
semiconductor laser: The type of laser used in a CD-ROM drive. Also called a “laser diode.”
sequential access: The retrieval of data by scanning a storage medium sequentially until the data is located.
serial I/O: The processing of input and output sequentially rather than in parallel.
server: A program or device that provides functionality for other devices, or clients.
Service Advertising Protocol (SAP): A broadcast mechanism found in versions of Novell NetWare that is used to send information over a wide-area network.
servo mechanism: A small, precise motor. A typical CD-ROM drive, for example, contains four. Also referred to as a “servo.”
SGML: See “Standard Generalized Markup Language.”
shareware: Commercial software that is distributed collectively on CD-ROM or via other electronic media. You are free to try the software, but expected to pay for it if you find it worthwhile.
signal-to-noise ratio (SNR): In a computer sound board, the difference in decibels between the lowest and highest sounds a board can generate. The higher the SNR, the more realistic the sounds. CD-quality sound has an SNR of about 100dB.
single session: A CD-ROM drive that cannot read a partially recorded disc (one that has been recorded in multiple sessions).
single-speed drive: A CD-ROM drive that reads data at a rate of 150Kbps.
site license: An agreement between a software or service provider and a customer where the customer pays one fee to use the product at a particular location or within the entire company. The amount of a site license might depend on the number of people using it (seats), number of servers or systems that access or store a client, or the amount of data used.
Small Computer System Interface (SCSI): A high-level bus standard that was once the preferred method to connect storage devices to computers.
SMP: See “symmetric multiprocessing.”
SNA: See “Systems Network Architecture.”
SNR: See “signal-to-noise ratio.”
software: Programs, operating systems, and embedded code that computers and other electronic devices use.
son: A metal die created from the mother die during the compact disc manufacturing process. Also called a “daughter.”
sprite: Small graphics pictures or a series of pictures that can be moved independently around the screen to create the effect of animation.
stamper: The metal die actually used to press compact discs.
Standard Generalized Markup Language (SGML): A scripting language used to represent the structure of an electronic document. A forerunner of the Hypertext Markup Language (HTML) used on the web today.
subcode byte: An auxiliary signal read by the CD-ROM drive’s circuitry that contains the address (same as the header value), track number, and detection symbols.
substrate: The plastic portion of a compact disc.
symmetric multiprocessing (SMP): A system architecture that permits the use of more than one main processor of an identical type where each has shared access to main memory and all I/O devices. All are controlled by a single operating system instance.
sync bytes: The identifying part of each sector on a CD-ROM.
syntax: The rules that define properly constructed code for a computer language.
synthesizer: The part of a computer sound board that reproduces specific sounds, such as a musical instrument or speech.
system: The computer or network with all its basic components (keyboard, storage, video, etc.).
Systems Network Architecture (SNA): A proprietary networking architecture that IBM developed in 1974. It establishes protocols for interconnecting computers and peripherals.
tape backup: An archival storage system that uses magnetic tape media.
TCP/IP: See “Transmission Control Protocol and Internet Protocol.”
Telenet: An early U.S.-based packet-switched network that was launched in 1974, the first to be available to the general public.
Teletype: A type of terminal made by Teletype Corp. with a keyboard and printer output.
teletypewriter (TTY): A type of terminal.
terminal: A keyboard or video unit connected to a computer that is used to input data or view output. Some terminals also have the ability to print output.
terminal emulation: The ability for one type of terminal to imitate another type for the sake of compatibility across a network.
terminate and stay resident (TSR): Software that loads into high memory and remains dormant until needed. Most drivers are TSRs.
terminator: A resistor placed at the end of a chain of SCSI devices that reduces signal noise.
text editor: A program that allows a person to edit plain text.
texture mapping: The act of wrapping an image onto other 3D objects.
THD: See “total harmonic distortion.”
thermal recalibration: A function that a hard disk drive performs to compensate for physical changes in the recording surface caused by temperature variations.
throughput: The amount of data that a system can process in a given amount of time, from input to output.
time sharing: A method that allows multiple people using remote terminals, computers, or other devices to use a specific computer at the same time.
Token Ring: A networking protocol where all the computers are connected in a ring or star topology. Developed by IBM, it became the IEEE 802.5 standard.
total harmonic distortion (THD): The amount of total distortion or background noise a computer sound board generates, measured in percent. A good THD is in the 0.5% range.
track: Both optical media and rotating magnetic media arrange data in tracks. On a CD-ROM, the tracks are arranged in a spiral and logically separated according to how the files are arranged. On rotating magnetic media, the tracks are concentric and physically discrete.
track-at-once: The process of recording an entire CD-R disc at once.
transceiver: An electronic component or device that can transmit and receive communications.
transformer: A device that sends power from one circuit to another at the same frequency but different voltage and current.
transistor-transistor logic (TTL): A type of semiconductor design that is built from bipolar junction transistors.
Transmission Control Protocol and Internet Protocol (TCP/IP): A set of communications protocols that support peer-to-peer connectivity for both local and wide-area networks. It is also the foundation of the internet.
transportable: a computer designed to be transportable, but too large or heavy to use during transit.
triple-speed drive: A CD-ROM drive that reads data at 450Kbps, three times the single-speed rate.
TSR: See “terminate and stay resident.”
TTL: See “transistor-transistor logic.”
TTY: See “teletypewriter.”
turntable controller: The circuitry in a CD-ROM drive that controls the servo that rotates the disc.
Tymnet: An international packet-switched data network used to connect host computers at large companies and public organizations.
UI: See “user interface.”
uninterruptible power supply (UPS): An external power source used to power computers and other devices in the event of a power failure.
UNIX: A multi-user, multitasking operating system developed in the 1970s but still widely used in business. The many UNIX variants include Microsoft’s Xenix and Apple’s A/UX.
UPS: See “uninterruptible power supply.”
user interface (UI): The point at which interaction between humans and computers occur.
utility: Software that is designed to maintain, troubleshoot, configure, or optimize a computer.
value-added reseller (VAR): A reseller that bundles other vendors’ products or services and adds value by adding capabilities or customizing for the customer.
VAR: See “value-added reseller”
VersaModule Eurocard bus (VMEbus): A 32-bit bus developed by Motorola and a consortium of companies and based in part on Motorola’s VersaBus and the Eurocard standard. Commonly used by 68xxx-based systems.
very large-scale integrated circuits (VLSI): Circuits that contain millions of MOS transistors on a single chip.
VESA Local Bus (VL-Bus): A local bus standard for Intel 486 systems.
VMEbus: See “VersaModule Eurocard bus.”
VGA: See “Video Graphics Array.”
VHS: See “Video Home System.”
Video CD: A format standard that covers the use of video sequences on CD-ROM. It uses the MPEG compression algorithm and is also called the “Karaoke CD” standard.
Video Graphics Array (VGA): An IBM video standard for PCs that supports 640 x 480 graphics and up to 256 colors.
Video Home System (VHS): A standard for recording consumer video on tape cassettes, developed by Victor Company of Japan (JVC) and released in 1976.
Videotext or Videotex: A standard and technology for delivering text and graphic information to a TV or video terminal.
virtual reality (VR): A 3D simulation technique that immerses the viewer into the image being viewed. Virtual reality applications usually require the use of a special optical helmet or visor.
virus: Computer code designed to clandestinely infect a computer and perform unwanted tasks. A virus can be destructive or simply annoying.
VL-Bus: See “VESA Local Bus.”
VLSI: See “very large-scale integrated circuits.”
voice: A specific synthesized sound made by a computer sound board.
volume: In computing, a volume refers to a logical drive for data storage.
volume descriptor: Data placed on a storage medium that contains information about a related set of files.
VR: See “virtual reality.”
WAN: See “wide-area network.”
wide-area network (WAN): A network that connects LANS that are in separate locations.
waveform audio: Sound that is played digitally.
wavelength: A measured distance traveled by a beam of light.
White Book: See “CD-I Bridge.”
workgroup computing: A cluster of computers and software serving individual workers who typically share a common supervisor and share the same mission or goal. A workgroup system allows those workers to share files and resources, and to connect to larger networks or workgroups.
workstation: A computer designed for a professional application such as engineering or science. The term is often used to refer to any individual computer on a network, however.
WORM: See “write once, read many.”
write once, read many (WORM): An optical storage technology used primarily for archival storage.
X.25: An ITU-T standard protocol suite for packet-switched wide area networks.
X.400: An ITU-T suite of protocols for email systems.
Xenix: Microsoft’s version of AT&T UNIX.
Xerox Network System (XNS): A set of networking protocols developed in the 1980s.
XNS: See “Xerox Networking Standard”
XON/XOFF: A protocol to control data flow between computers and other devices over an asynchronous serial connection.
Xerox PARC: A research and development company founded by Xerox in 1970.
Yellow Book: The basic format standard for CD-ROM, developed by Philips and Sony.
Classic Tech 