10 Gigabit Ethernet — Network transmission method based on the IEEE 802.11ae and 802.11ak standards.

1GL — Acronym of first generation language.

24-bit color — Coding method that represents a color as three 8-bit numbers, one for the intensity of each additive or subtractive color.

2GL — Acronym of second-generation language .

3GL — Acronym of third-generation language .

4GL — Acronym of fourth-generation language .

5GL — Acronym of fifth-generation language .

802.11 — Early IEEE wireless network standard with a 2 Mbps maximum transmission speed in the 2.4 GHz band .

802.11a IEEE wireless network standard with a 54Mbps maximum transmission speed in the 5 GHz band using orthogonal frequency division multiplexing.

802.11b IEEE wireless network standard with an 11 Mbps maximum transmission speed in the 2.4 GHz band using direct sequence spread spectrum transmission.

802.11g IEEE wireless network standard with a 54 Mbps maximum transmission speed in the 2.4 GHz band using orthogonal frequency division multiplexing.

absolute addressing — Describes memory address operand s that refer to actual physical memory locations.

access arm — Device within a disk drive containing one or more read/write head s mounted at one end. The other end is attached to a motor that allows enables the read/write head (s) to be positioned over a single track of the disk platter .

access control list — List of users or user groups with access authority to a secured object or service.

access time — Elapsed time between the receipt and completion of a read or write command by a storage device.

acknowledge (ACK) ASCII control character sent from receiver to sender to indicate successful receipt of transmitted data.

ACK — Mnemonic of the acknowledge ASCII control character .

ACL — Acronym of access control list .

ACM — Acronym of Association for Computing Machinery .

Active Directory (AD) — Microsoft directory services software.

active matrix display — Liquid crystal or plasma display that uses one or more transistor s for every pixel .

AD — Acronym of Active Directory .

ADC — Acronym of analog-to-digital conversion.

ADD — (1) Boolean operation that computes the arithmetic sum of two numbers. (2) Central processing unit instruction that computes the arithmetic sum of two numbers and store s it in a register or memory location.

additive colors — Red, green, and blue.

address — Physical location of a data item (or the first element of a set of data items) within a storage or output device.

address bus — Portion of a bus that transmits the address of a storage location to be read from or written to.

address mapping — Synonym of address resolution .

address resolution — As performed by the control unit , converting relative or segmented address references into corresponding physical memory addresses.

addressable memory — Maximum amount of memory that can be addressed physically by the CPU .

Advanced Intelligent Tape (AIT) Magnetic tape standard developed by Sony based on Digital Audio Tape technology.

AIT — Acronym of Advanced Intelligent Tape .

AITP — Acronym of Association for Information Technology Professionals .

algorithm — (1) Series of processing steps that describes the solution to a problem. (2) Sequence of instruction s within a computer program that implements a complex processing operation.

allocation unit — Smallest unit of storage that can be allocated to an object such as a file or a program .

ALU — Acronym of arithmetic logic unit .

AM — Acronym of amplitude modulation .

American Standard Code for Information Interchange (ASCII) — Standard 7-bit coding scheme for character data and a limited set of I/O device control function s.

amplifier — Hardware device that increases the amplitude or power of a signal or waveform.

amplitude — Magnitude (highest value) of wave peaks of a waveform.

amplitude modulation (AM) — Data transmission method that en code s data values as variations in carrier wave amplitude .

amplitude shift keying (ASK) — Synonym of amplitude modulation .

analog signal — (1) Signal in which any value of an infinite set can beis encoded by modulating one or more carrier wave parameters in direct proportion to the encoded value. (2) Signal that varies continuously in one or more carrier wave parameters, such as frequency or amplitude .

analog-to-digital converter (ADC) — Processing device that generates a numerical representation of an analog waveform, see sampling .

AND — (1) Boolean operation that generates the output value false unless both input values are true. (2) Central processing unit instruction that generates the output value false unless both input values are true, and store s the result in a register or memory location.

applet Program written in the Java programming language that is executed by another program such as a Web browser.

application development software — Software tools such as compiler s and CASE tools used to develop application software .

application firewall Server that handles the service requests of external users of one or more applications, thus shielding other server s from direct access and potential security breaches.

application layer Application program s (software), as compared to systems software and computer hardware.

application program Program that addresses a single specific need of a user or a specific class of information processing tasks.

application programmer — Per son who creates or maintains application software .

application software — Software class consisting of all application program s.

architectural design — Selecting and describing the exact configuration of all hardware, network, systems software, and application development tools that will support system development and operations.

areal density — Surface area allocated to a bit on a storage medium , typically as measured in bit s, byte s, or track s per inch.

arithmetic logic unit (ALU) — Circuitry within a central processing unit that performs computation, comparison, and Boolean logic operations.

arithmetic SHIFT SHIFT operation that performs division or multiplication.

array — Set of data items stored in consecutive storage areas and identified by a common name.

ASCII — Acronym of American Standard Code for Information Interchange .

ASK — Acronym of amplitude shift keying.

assembler Program that translates assembly language source code instruction s into object code or central processing unit instruction s.

assembly language Programming language that uses mnemonics to represent central processing unit instruction s and storage address operand s.

Association for Computing Machinery (ACM) — Professional organization for computer scientists, programmer s, and engineers.

Association for Information Technology Professionals (AITP) — Professional organization for information system professionals.

asynchronous transfer mode (ATM) — Protocol for high-speed data transmission that uses hardware-based packet switching and routing and provides quality of service guarantees.

asynchronous transmission — Any transmission method in which sender and receiver do not continually synchronize their clocks.

ATM — Acronym of asynchronous transfer mode .

attenuation — Reduction in signal amplitude or power that occurs as the signal travels through a transmission medium .

audio response unit — Device that provides natural language instruction s or responses to input from the keypad of a telephone or other device.

auditing Process of creating and managing record s of user activity or resource access.

authentication Process of determining or verifying the identity of a user or process owner.

authorization Process of determining whether an authenticated user or process has sufficient rights to access a particular resource.

average access time — Statistical average (or mean) elapsed time required by a storage device to respond to a read or write command.

back-end CASE tool — Software tool that creates source code instruction s from a system model.

band — Portion of the message-carrying capacity of a carrier wave or transmission medium , typically expressed as a range of frequencies, such as the band between 200 and 1,0002.4 and 2.5 gigahertz .

bandwidth — Range of carrier wave frequencies that can be transmitted over a transmission medium .

bar code — Set of dark vertical bars or a two-dimensional pattern of dark squares that en code s numerical data and can be read by a bar code scanner or other optical scanning device.

bar code scanner — Device that optically scans surfaces for numbers encoded in bar code s.

base — Multiplier that describes the difference between one position and the next in a numbering system.

baseband — (1) Transmission method that uses the entire bandwidth of a communication channel to carry one signal or data stream. (2) Local area network transmission method in which multiple digital signal s are carried over a single communication channel through time-division multiplexing.

BCC — Acronym of block check character .

BCD — Acronym of Binary Coded Decimal .

benchmark Program , program fragment, or set of program s and related data inputs that test the performance of a hardware component , a group of hardware or software component s, or an entire computer system or network when executing one or more specific tasks.

big endian — Describes a CPU architecture that store s a multibyte data item with the most significant byte in the storage location with the lowest-numbered address .

Binary Coded Decimal (BCD) — Antiquated 6‑bit cha character ding met method ed by early IBM computer systems.

binary number — Number in which each digit can have only one of two possible values (0 or 1).

binary signal Signal in which one of two values is encoded by modulating a carrier wave parameter.

biometric authentication Authentication based on physical characteristics such as fingerprint or retinal scanning.

bit — (1) Value represented in a one position of a binary number. (2) Number that can have a value of zero or one. (3) Abbreviation of binary digit.

bit map — Image representation in which each pixel is represented by one or more bit s.

bit string — Sequence of bit s that describes a single data value.

bit time — Time interval during which the value of a single bit is present within a transmitted signal .

blade — Circuit board that contains most of a server computer.

block — (1) Series of logical record s grouped on a storage device for efficient processing, storage, or trans port . (2) Unit of data transfer to and from a storage device. (3) Portion of a program that is always executed as a unit.

block check character (BCC) — Extra 8-bit value containing error-detection information that is appended to the end of a set, or block , of transmitted data items.

block checking — Synonym of longitudinal redundancy checking .

block size — Number of bit s, byte s, or record s within a single storage block or allocation unit .

blocked state — State of a process or thread that is waiting for an event such as completion of another process or thread , arrival of data input, or correction of an error condition .

blocking — Storage of multiple data items or data item fragments within a single storage block or allocation unit .

blocking factor — The number of bit s, byte s, or logical record s grouped within a single physical record , storage block , or allocation unit .

Bluetooth — Wireless networking standard that forms ad-hoc networks using radio frequency transmission over distances up to 10 meters.

Boolean data type — Data item class that can store only the value true or false.

Boolean logic — Formal logic system in which data inputs and outputs can have only the values of true or false.

BRANCH — (1) Processor operation that causes an instruction other than the next sequential instruction to be fetched and executed. (2) Processor instruction that implements a BRANCHbranch operation by overwriting the current value of the instruction pointer .

branch prediction — Technique to increase the benefits of pipelining in which the CPU guesses whether a branch condition will be true or false based on past experience.

bridge — Device that copies or repeats packet s from one network segment to another.

broadband — (1) Communication channel with a wide frequency range and high data-transmission capacity. (2) Transmission method in which multiple digital signal s are carried over a single channel through frequency division multiplexing.

broadcast mode — Transmission method that sends a message from a sender to all devices on a communication channel .

brownout — Reduction in voltage by an electrical power provider, usually because of temporary excess of power demand over available supply.

buffer Primary storage that temporarily store s data in transit from a sender to a receiver.

buffer overflow — Receipt of more data than can be stored in a buffer .

bus Communication channel shared by multiple devices within a computer system or network.

bus arbitration unit Processor that mediates competing demands for control of or access to a bus .

bus clock — Clock circuit that generates timing pulses, which are transmitted to all devices attached to a bus .

bus cycle — (1) Period of time required to perform one data transfer operation on a bus . (2) Elapsed time between two consecutive pulses of a bus clock.

bus master — (1) Any device attached to a bus that can initiate a data-transfer operation or send a command to another device. (2) Device that controls a data-transfer operation during a specific bus clock cycle .

bus protocol Communication protocol used by all devices attached to a bus .

bus slave —Device that is incapable of acting as a bus master.

bus topology — With respect to data communication networks, a topology that uses a bus as the communication channel .

business logic layer — Software layer or component that implements the rules and procedure s of business processing.

business modeling discipline — Activities of the Unified Process that develop models of an organization and the system environment.

byte String of eight bit s.

cache — Area of high-speed memory that holds portions of data also held within another storage device. A cache improves the average speed of read and write operations to or from its associated storage device.

cache controller Processor or software that manages cache content.

cache hit — Access to data in a storage device also stored in a cache .

cache miss — Access to data in a storage device that is not also stored in cache .

cache swap — Operation that copies data from a cache to its associated storage device and then overwrites the cache copy with new data.

call Instruction that execute s a function , subroutine , or procedure .

capital expenditure — Funds expended to obtain a capital resource .

capital resource — A resource expected to provide benefits beyond the current operating period.

Carrier Sense Multiple Access/Collision Detection (CSMA/CD) Media access control protocol that allows message collision s to occur but defines a recovery method .

carrier wave — Energy wave such as electricity or light that carries encoded message s within a communication channel .

CASE — Acronym of computer assisted software engineering.

Category 5 — Widely implemented twisted pair wiring standard that consists of four twisted pairs that transmit at speeds of up to 1 Gbps.

Category 6 — Twisted pair wiring standard with the same construction as Category 5 but higher qualitywire and insulators to reduce transmission errors.

cathode ray tube (CRT) — Video display device that uses electron beams to excite phosphor(s) on the inner surface of a vacuum tube.

CD-DA — Acronym of compact disc–digital audio .

CD-R — Acronym of compact disc–recordable .

CD-ROM — Acronym of compact disc read-only memory .

CD-RW — Acronym of compact disc–read/write .

central processing unit (CPU) — Computer system hardware component that fetches and execute s instruction s.

channel — (1) Synonym of input/output channel . (2) Shortened form of communication channel .

character — (1) Primitive and indivisible component of a written language. (2) One byte of ASCII-encoded data or two byte s of Unicode-encoded data.

character framing — Serial data communication technique that surrounds encoded character s with specific bit patterns for purposes of clock synchronization and error detection.

chief information officer (CIO) — Manager charged with responsibility for planning, maintaining, and operating all information-processing resources within an organization.

child process Process created and controlled by another executing process (the parent process ).

chromatic depth — Synonym of chromatic resolution .

chromatic resolution — (1) Number of bit s used to describe the color of each pixel in a graphic display. (2) Number of different colors that may be assigned as the value of any single pixel .

CIO — Acronym of chief information officer .

circuit switching — Technique for allocating transmission lines or circuits to senders and receivers whereby a sender and receiver are granted exclusive use of a communication channel for the duration of a communication session.

CISC — Acronym of Complex Instruction Set Computing .

class Data structure that contains both traditional data elements and the software that manipulates the data elements.

client Program or computer that requests and receives services from another program or computer.

client-server architecture — Organization of software and hardware component s as client s and server s.

clock cycle — Time interval between two adjacent clock timing pulses.

clock rate — (1) Rate at which clock pulses are generated by a clock, stated in hertz . (2) With respect to a central processing unit , the time required to fetch and execute the simplest instruction .

cluster — A group of similar or identical computers, connected by a high-speed network, that cooperate to provide services or execute a common application.

CMY — Acronym of cyan, magenta, yellow.

CMYK — Acronym of cyan, magenta, yellow, black.

coaxial cable Transmission medium composed of a single strand of wire surrounded by an insulator, a braided return wire , and a tough outer coating.

code — (1) Act of creating program instruction s. (2) A program or set of related source or machine code instruction s.

code generator — Synonym of back-end CASE tool .

coercivity — Ability of an element or compound to accept and hold a magnetic charge.

collating sequence — Order of symbols produced by sorting them according to a numeric interpretation of their coded values.

collision — Result of simultaneous transmission by two senders on a shared communication channel .

COM+ — Acronym of Component Object Model Plus.

command language — A language that directs an operating system’s actions.

command layer System software component that accepts and processes user commands to manipulate software, stored data, and hardware resources.

Common Object Request Broker Architecture (CORBA) — Nonproprietary standard that enables software component s to locate and communicate with one another.

communication channel — Combination of a transmission medium and communication protocol .

communication protocol — Set of communication rules and conventions encompassing data and command representation, bit encoding and transmission, transmission media access, clock synchronization, error detection and correction, and message routing.

compact disc–digital audio (CD-DA) — Standard format for storing and distributing music on compact disc.

compact disc–read only memory (CD-ROM) — Standard 120 millimeter read only optical disc.

compact disc–read/write (CD-RW) — Standard phase-change optical storage method and medium.

compact disc–recordable (CD-R) — Compact disc containing a laser-sensitive dye that can be written with a laser switched between high and low power.

compaction Process of reallocating storage locations assigned to one or more files or program sa file[SB2] to eliminate empty storage locations.

competitive advantage — Use of resources to provide better or cheaper services than others can provide with those same resources.

compiler Program that translates high-level programming language source code instruction s into object code .

compiler library — Set of object-code modules intended to be linked with object-code modules produced by a compiler .

complete path — Named path from the root node of a storage volume or name space to a specific file or object through intervening layers of a hierarchical directory structure .

complex instruction Instruction that combines primitive processing operations.

Complex Instruction Set Computing (CISC) Processor architecture that uses complex instruction s that embed many primitive processing operations, in contrast to reduced instruction set computing.

component — Executable software module or object with a well-known interface and a unique identifier.

Component Object Model Plus (COM+) — Microsoft proprietary standard that enables software component s to locate and communicate with one another.

compression — Reduction in data size using a compression algorithm .

compression algorithm Algorithm by which data inputs may be translated into equivalent outputs of smaller size.

compression ratio — Ratio of data size before and after applying a compression algorithm .

computer assisted software engineering (CASE) tool Program or integrated set of program s used to analyze, design, and develop computer software.

computer network — Hardware and software that enables multiple users and computer systems to share information, software, and other resources.

computer operations manager — Manager responsible for the operation and maintenance of a large data-processing center or information system.

computer science — Study of the implementation, organization, and application of computer software and hardware resources.

concurrent execution — Execution of multiple processes or thread s within the same immediate time frame through interleaved execution on a single processor .

condition — A comparison or other logical operation that produces a Boolean result.

conditional BRANCH — (1) BRANCH operation that is performed only if a Boolean variable is true. (2) Processor instruction that implements a conditional BRANCH operation.

conductivity — Ability of a transmission medium to allow an energy wave such as electricity or light to pass through a conductor or transmission medium .

conductor — Element, compound, wire , or cable that exhibits conductivity .

connection-oriented protocol Communication protocol that requires sender and receiver to establish a connection prior to transmitting any data.

connectionless protocol Communication protocol that does not require sender and receiver to establish a connection prior to transmitting any data.

contiguous — Storage of a set of data elements in sequential physical storage locations with no intervening empty or unallocated locations.

control bus — Portion of a bus that transmits command and status signal s.

control structure — High-level programming or job control language statement that describes the selection or repetition of other program statements, such as an If-Then or While-Do statement.

control unit — Subset of a central processing unit responsible for moving data, accessing instruction s, and controlling the arithmetic logic unit .

CORBA — Acronym of Common Object Request Broker Architecture .

core memory — Antiquated form of primary storage implemented as a lattice of wire s with iron rings wrapped around each wire junction point .

CPU — Acronym of central processing unit .

CRC — Acronym of cyclical redundancy checking .

crosstalk Noise added to the signal in a wire from EMI generated by adjacent wire s.

CRT — Acronym of cathode ray tube .

CSMA/CD — Acronym of Carrier Sense Multiple Access/Collision Detection .

current directory Directory that serves as the origin for file and directory search operations.

cursor — Visual symbol on a video display, such as a colored box or underline, that indicates the current input or output position.

cycle — Single operation, function , or transfer within a series of similar operations, function s, or transfers, as performed by a processor , storage device, or communication channel .

cycle time — Duration of one cycle .

cyclical redundancy checking (CRC) — Technique for detecting errors in data transmission based on redundant data computed with a complex algorithm and appended to the original message .

cylinder — In a disk storage device, the set of all track s at an equivalent distance from the edge or spindle on all recording surfaces.

DAC — Acronym of digital-to-analog converter .

DAS — Acronym of direct-attached storage .

DAT — Acronym of Digital Audio Tape .

data bus — Portion of a bus that transmits data.

data declaration Programming language statement that declares the existence, name, type, and other characteristics of a data item or structure.

data layer — Software layer or component that manages and interacts with a permanent data store such as a database.

data link layer — Layer of network system software responsible for media access and bit transmission.

data operation — Any processing operation that uses or alters data content.

data striping — Data storage method that improves read/write performance by dividing data into smaller segments and storing the segments on multiple disks.

data structure — A data item, such as an array or linked list , that contains multiple primitive data elements or other data structure s.

data transfer rate — Rate at which data is transmitted through a medium or communication channel , as measured in data units per time interval.

database administrator — Manager responsible for ensuring data integrity, reliability, security, and availability.

datagram — Smallest unit of data transfer defined by the Transmission Control Protocol .

DCE — Acronym of Distributed Computing Environment .

DDS — Acronym of Digital Data Storage .

debugging tools — Type of application development software that simulates program execution and trace s errors.

debugging version Program that contains data and instruction s to aid in locating and correcting errors.

decimal point — Period or comma in the decimal numbering system that separates the whole and fractional parts of a numeric value.

decoding Process within the central processing unit of extracting the op code and operand s, routing data and control signal s, and signaling the ALU .

decompression algorithm Algorithm that return s compressed data to its original state.

deployment discipline — Activities of the Unified Process that install and configure infrastructure and application software component s and bring them into operation.

design discipline — Activities of the Unified Process that determine the structure of a specific information system that fulfills the system requirements.

design model — Architectural blueprint for system implementation that is an output of the design phase .

detailed design — Design activities that specify system details including databases, application software , user and system interfaces, and backup and recovery mechanisms.

device controller Processor that controls the physical actions of one or more storage devices.

Digital Audio Tape (DAT) — Early magnetic tape technology on which Digital Data Storage standards are based.

Digital Data Storage (DDS) — Family of magnetic tape standards developed by Hewlett-Packard and Sony, and based on Digital Audio Tape .

Digital Linear Tape (DLT) Magnetic tape standard developed by Quantum.

digital signal — (1) Signal in which one of a discrete, or countable, set of values can be encoded by modulating one or more carrier wave parameters. (2) Synonym of binary signal .

digital signal processor (DSP) Processor that manipulates continuous streams of digital data, such as audio or motion video.

digital-to-analog converter (DAC) — Processing device that generates an analog signal from a numerical representation of the signal .

digital versatile disc (DVD) — Synonym of digital video disc .

digital video disc (DVD) — Standard optical disc format for distributing movies and other audio-visual content.

digital video disc random access memory (DVD‑RAM) — Standard for rewriteable digital video disc s with a capacity of 2.4 GB for single-sided discs and 4.8 GB for double-sided discs.

digital video disc read-only memory (DVD‑ROM) — Standard format for general-purpose read-only data storage on digital video disc .

digitizer — (1) Device that captures the position of a pointing device as input data. (2) Synonym of optical scanner .

DIMM — Acronym of double in-line memory module .

DIP — Acronym of dual in-line package .

direct access — Synonym of random access .

direct-attached storage (DAS) — Architecture in which software executing on a CPU accesses secondary storage devices within the same computer system.

direct memory access (DMA) Method of data transfer that allows enables direct data movement between main memory and a storage or I/O device, bypassing the central processing unit .

directory Data structure that contains information about files and other directories.

directory services System software ( middleware ) that enables users and component s to locate and access remote resources.

discipline — Related group of system development activities within the Unified Process .

discrete signal — Synonym of digital signal .

disk defragmentation — Reorganization of data on a disk drive so that all portions of an individual file are stored in contiguous sequential sector s.

disk mirroring — Storage technique that enhances reliability by storing a redundant copy of all data on a second disk drive.

diskette — Synonym of floppy disk .

dispatching — (1) Act of giving a process or thread control of the central processing unit . (2) Act of moving a process or thread into the running state .

distortion — Undesirable alteration of one or more carrier wave characteristics resulting from interaction between signal energy and the transmission-medium or signal-propagation equipment.

distributed computing — Synonym of distributed processing .

Distributed Computing Environment (DCE) — Standard for distributed processing that covers network directory services, file sharing services, remote procedure call s, remote thread execution, system security, and distributed resource management.

distributed processing — Distribution and execution of processes or thread s over multiple nodes of a computer network .

distribution version — Synonym of production version .

dithering — Simulating continuous color tones using patterns of dots containing a finite set of colors.

DLL — Acronym of dynamically linked library.

DLT — Acronym of Digital Linear Tape .

DMA — Acronym of direct memory access .

DMA controller — Dedicated processor that handles the processing of manages data transfers during direct memory access operations.

dot matrix printer — Impact printer that generates printed character s using a matrix of pins and an inked ribbon.

dots per inch (dpi) — Measure of print or display resolution ( pixel density).

double in-line memory module (DIMM) — Small standard printed circuit board containing one or more random access memory chips with electrical contacts on both sides.

double precision — Representing a numeric value with twice the usual number of bit positions for greater accuracy or numeric range .

doubly linked list — Set of stored data items in which each element contains pointer s to both the previous and next list elements.

dpi —Acronym of dots per inch .

DRAM — Acronym of dynamic random access memory .

drive array — Set of disk drives managed and accessed as if they were a single storage device.

DSP — Acronym of digital signal processor .

dual in-line package (DIP) — Early form of packaging for processor or memory circuits with two rows of electrical contact pins

dual porting — With respect to random access memory , the ability to be read and written at the same time by two different devices.

DVD — Acronym of both digital video disc and digital versatile disc .

DVD-RAM — Acronym of digital video disc random access memory .

DVD-ROM — Acronym of digital video disc read-only memory .

DVD-RW — (1) Acronym of digital video disc read-write. (2) Rewritable DVD standard supported by the DVD Forum.

DVD+RW — (1) Acronym of digital video disc read-write. (2) Rewritable DVD standard supported by Hewlett-Packard, Philips, and Sony.

dynamic connection — Connection between a client and a server or remote resource that is not established until the client accesses the server or resource.

dynamic linking — Linking performed during program loading or execution.

dynamic random access memory (DRAM) — Type of electronic memory circuit that implements bit storage with transistor s and capacitors.

dynamically-linked library (DLL) — (1) A library of reusable software modules organized for dynamic linking . (2) A specific Microsoft Windows file format for storing reusable software modules.

early binding — Synonym of static linking .

EBCDIC — Acronym of Extended Binary Coded Decimal Interchange Code .

EDRAM — Acronym of enhanced dynamic random access memory .

EEPROM — Acronym of electronically erasable programmable read-only memory .

effective data transfer rate — Error-free throughput of a communication channel under normal condition s with a specific communication protocol .

EJB — Acronym of enterprise Java bean[SB3] .

electromagnetic interference (EMI) — Alteration of electrical carrier wave characteristics caused by external electrical or magnetic phenomena, such as electric motors or sun spots.

electronically erasable programmable read-only memory (EEPROM) Read-only memory device that can be erased and written by sending appropriate control signal s.

enterprise Java bean (EJB) [SB4] —Java program that execute s within a business container on a server .

EMI — Acronym of electromagnetic interference .

enhanced dynamic random access memory (EDRAM) — Type of electronic memory circuit primarily composed of DRAM but supplemented with a small SRAM cache .

EPROM — Acronym of erasable programmable read-only memory .

erasable programmable read-only memory (EPROM) Read-only memory device that is manufactured blank, is written (programmed) with a special EPROM writer, and erased by exposure to ultraviolet light.

Ethernet — Widely implemented local area network standard family.

even parity — Error-detection method that appends a parity bit to each transmitted or stored character . The value of the parity bit is zero if the number of one valued bit s in a character is even; it is one otherwise.

excess notation — Coding method that represents integer values as bit string s such that the value zero (the midpoint of the numeric range ) is represented by all zero bit s except for the most significant bit (which contains a one).

exclusive OR (XOR) — (1) Boolean operation that generates the output value true if only one of the input values is true. (2) CPU instruction that generates the output value true if only one of the input values is true.

executable code Program that consists entirely of CPU instruction s that are ready to be loaded and executed.

execute Process of carrying out an instruction within the central processing unit .

execution cycle Process of carrying out an instruction in the central processing unit and completing the operation it specifies.

explicit priority Process scheduling through explicitly stated priority levels and a corresponding scheduling algorithm .

Extended Binary Coded Decimal Interchange Code (EBCDIC) — IBM mainframe Standard coding system standard for representing character data in an 8-bit format, most commonly used with older IBM mainframe computers.

extensible markup language (XML) — Standard Web format that en code s document structure and content.

external function call — Placeholder within object code for missing executable code .

FAT — Acronym of file allocation table .

father — Original version of a file, after updates have been applied to generate a new version (the son ).

fault tolerance — Characteristic of a computer system or file management system that allows enables rapid recovery from the failure of a hardware component without data loss.

FCFS — Acronym of first come, first served .

FDM — Acronym of frequency division multiplexing.

ferroelectric random access memory — Type of non volatile random access memory that store s bit values within metallic crystals.

fetch cycle — Portion of a central processing unit cycle in which an instruction is loaded into the instruction register and decoded.

fiber-optic cable Transmission medium for optical signal propagation, generally consisting of one or more plastic or glass fibers sheathed in a protective plastic coating.

field Component data item of a record .

fifth-generation language (5GL) — Nonprocedural programming language used to develop software that mimics human intelligence.

file allocation table (FAT) Data structure used in MS-DOS and early Microsoft Windows versions to record the allocation of storage device locations to files and directories.

file association — Relationship between a file type and the program or operating system utility that manipulates it.

file close operation — Operation that severs the relationship between a file and a process , flushes file I/O buffer s, and deletes operating system data structure s associated with the file.

file control layer System software layer that accepts file manipulation requests from application program s and translates them into corresponding low-level processing commands to the central processing unit and secondary storage device controller s.

file management system (FMS) — Entire collection of system software that performs file management, usually part of the operating system .

file migration — Management technique for secondary storage in which older versions of a file are moved automatically to less costly storage media or devices such as magnetic tape .

file open operation Process of associating a file with an active process by allocating buffer s and updating internal tables.

File Transfer Protocol (FTP) — Older Web protocol for copying files from one Internet host to another.

firewall — Hardware device, software, or a combination of hardware and software that prevents unauthorized users in one network from accessing resources on another network.

firmware — Software that has been permanently stored in read-only memory devices.

first come, first served (FCFS) Scheduling method that execute s processes in order of their request arrival.

first-generation language (1GL) — Synonym of machine language or central processing unit instruction set.

fixed length instruction — One member of an instruction set in which all instruction s contain the same number of bit s.

flag — Single bit within a larger data unit or the program status word that represents one data item or condition .

flash memory — Type of electronically erasable read-only memory that requires relatively little time to update memory contents.

flash RAM — Synonym of flash memory .

flat memory model Memory organization and access method in which memory locations are described by single unsigned integer s that corresponds to linear position.

flat panel display — Display device that is thin, flat, and lightweight.

floating point notation Method of encoding real number s in a bit string consisting of two parts – a mantissa and exponent.

floppy disk — Small, removable magnetic disk storage medium encased in a protective cover.

FM — Acronym of frequency modulation .

FMS — Acronym of file management system .

font — Named set of display formats for printable character s and symbols with a similar appearance or style.

formula — Processing problem that can be solved by executing a fixed sequence of instruction s.

fourth-generation language (4GL) Programming language that supports nonprocedural programming, database manipulation, and advanced I/O capabilities.

fragmented — File or storage device characteristic in which noncontiguous storage locations are allocated to one or more files are scattered in noncontiguous locations.

frequency — Number of complete waveform transitions (change from positive to negative to positive energy peak) that occur in one second.

frequency division multiplexing (FDM) — Communication channel-sharing technique in which a single broadband channel is partitioned into multiple baseband subchannels ( frequency band s), each of which can carry a separate data stream.

frequency modulation (FM) — Data transmission method that en code s data values as variations in carrier wave frequency .

frequency shift keying (FSK) — Synonym of frequency modulation .

front-end CASE tool Program that supports creating and modifying system models.

front-end processor — Synonym of I/O channel , particularly as applied to minicomputer s and mainframe s not manufactured by IBM.

FSK — Acronym of frequency shift keying.

FTP — Acronym of File Transfer Protocol .

full backup — Data store containing copies of all data in a directory or storage device.

full-duplex — Type of communication channel composed of two transmission media that allows enables simultaneous communication in both directions.

fully qualified reference — Synonym of complete path with respect to a specific file or object .

function — Named segment of a high-level language program that is always executed as a unit.

gallium arsenide — Compound with both electrical and optical properties.

gate — Processing device that implements a primitive Boolean operation or processing function by physically transforming one or more input signal s.

gateway — Computer system or hardware device that is connected to two or more network segments and forwards packet s among the segments.

general-purpose processor Processor that can be directed to perform a wide variety of specific processing tasks.

GHz — Abbreviation of gigahertz .

GIF — Acronym of Graphics Interchange Format .

Gigabit Ethernet — High-speedOne gigabit per second Ethernet standard based on the 802.3z and 802.3ab standards.

gigahertz (GHz) — Unit of wave or clock frequency , one billion cycle s per second.

grandfather — Version of a file prior to the father version.

graph directory structure — (1) Directory structure in which allowable relationships between directories can be represented as a graph. (2) Directory structure in which a file or subdirectory can be contained within two or more directories.

graphics accelerator — High-performance video controller with an embedded processor and software that converts incoming image description language commands into appropriate input to a video display.

Graphics Interchange Format (GIF) — Standard format for storing compressed images.

grayscale — Describes a display device or image encoding method that can display or represent, black, white, and shades of gray, but no other colors.

grid — Group of dissimilar computer systems, connected by a high-speed network, that cooperate to provide services or execute a common application.

Grosch’s Law — Outdated mathematical relationship between computer size and cost per unit of instruction execution that states that cost per executed instruction decreases as computer system size increases.

half-duplex — Type of communication channel that uses only a single transmission medium where sender and receiver take turns transmitting data to one another.

half-toning — Simulating shades of gray with dithering using only two colors—black and white.

HALT Instruction that suspends the execution of any further instruction s by the central processing unit .

hard disk — (1) Storage medium consisting of a rigid platter coated with a metallic oxide on which data are recorded as patterns of magnetic charge. (2) Synonym of hard disk drive.

hardware independence — Independence of a program or processing method from the physical details of computer system hardware.

hardware monitor Program or device that record s and reports processing or communication activity within or between hardware devices.

HCA — Acronym of host channel adapter .

head-to-head switching time — Elapsed time required to switch shared read/write circuitry between two adjacent read/write head s.

heat dissipation — Conducting heat away from a device, thus reducing its temperature.

heat sink — Thermal mass placed in direct contact with a processor or other device to increase heat dissipation .

helical scanning — Tape recording method in which data is read and written by rotating the read/write head at an angle, moving from tape edge to tape edge.

hertz (Hz) — Unit of measure for signal frequency defined as one cycle per second.

hexadecimal notation — Numbering system with a base value of 16, which uses digit values ranging from 0 to 9 and from A to F (corresponding to decimal values 0 to 15).

hierarchical directory structure — Multilevel system of directories in which directories and files may be related to one another in a hierarchy or inverted tree.

high order bit — Synonym of most significant digit .

hit ratio — Ratio of cache hits to read accesses.

home directory — Primary directory associated with and owned by a single user.

Home Radio Frequency (HomeRF) — Home networking standard for devices connected within a 50 meter range.

HomeRF — Acronym of Home Radio Frequency .

host channel adapter (HCA) — Interface or controller that connects a device that can initiate or respond to data transfer commands to an Infiniband or Fibre Channel network.

HTML — Acronym of Hypertext Markup Language .

HTTP — Acronym of Hypertext Transport Protocol .

HTTPS — Acronym of Hypertext Transport Protocol Secure.

hub — Network interface device that serves as the network connection point for multiple computer systems.

Hypertext Markup Language (HTML) — Device-independent formatting language that describes Web documents and in which link s to other documents can be embedded.

Hypertext Transport Protocol (HTTP) — Protocol that specifies the language by which client s request HTML or XML documents and how server s respond to those requests.

Hypertext Transport Protocol Secure (HTTPS) — Encrypted version of the HTTP protocol.

Hz — Abbreviation of hertz .

H.323 — Oldest and most widely deployed VoIP protocol suite.

IA5 — Acronym of International Alphabet Number 5 .

IC — Acronym of integrated circuit .

ICMP — Acronym of Internet Control Message Protocol.

IDL — Acronym of image description language .

IEEE — Acronym of Institute for Electrical and Electronics Engineers.

IEEE 802 standards — Standard family for voice, data, and computer network s.

IIOP — Acronym of Internet Inter-ORB Protocol.

image description language — Language that symbolically describes the content of a printed or displayed image.

IMAP — Acronym of Internet Message Access Protocol.

implementation discipline — Activities of the Unified Process that build, acquire, and integrate application software component s.

inclusive OR — Synonym of OR operation.

incremental backup — Data store containing copies of data sets (files) that have been altered since the most recent incremental or full backup .

index — Stored set of paired data items. Each pair contains a key value and a pointer to the location of the data item possessing (or corresponding to) that key value.

indirect addressing — Any addressing method where a program’s memory address operand s do not necessarily correspond to physical memory storage locations.

Infiniband — Emerging sStandard for high-speed interconnect of computer network s, server s, and storage devices.

information architecture — Set of requirements and constraints that define important characteristics of information processing resources and how those resource interact with one another.

Infrared Data Association (IrDA) — Data communication standard based on infrared transmission.

infrastructure — Facilities or resources that provide services that are pervasively available and commonly used by a large numbers of users.

ink-jet printer — Printer that produces printed images by placing small drops of liquid ink onto paper.

input output (I/O) unit — Device that enables communication between a user and software or among computer systems or their component s.

input pad — Input device that converts pressure into usable computer input, such as for capturing written signatures or drawings.

Institute for Electrical and Electronics Engineers (IEEE) Computer Society — Subgroup of the IEEE that specializes in computer and data communication technology.

instruction Bit string containing an operation code and zero or more operand s that cause a processor to perform a processing operation.

instruction cycle — Synonym of fetch cycle .

instruction explosion — Correspondence of a single high-level programming language statement to multiple central processing unit instruction s.

instruction format — Length and order of the operation code and operand s within a machine language instruction .

instruction pointer Register that store s the address of the next instruction to be fetched from primary storage .

instruction register Register that holds an instruction prior to decoding .

instruction set — Set of all machine language instruction s that can be executed by a central processing unit .

integer — Whole number, or a value that does not have a fractional part.

integrated circuit (IC) Semiconductor device, manufactured as a single unit, that incorporates multiple gate s.

interleaved execution Scheduling technique by which a processor allocates CPU cycle s to multiple active processes in very small time slices.

International Alphabet Number 5 (IA5) — International equivalent of ASCII .

International Organization for Standardizations Organization (ISO) — International body with function s similar to those of the American National Standards Institute.

Internet — Global collection of networks interconnected using TCP/IP .

Internet Control Message Protocol (ICMP) Internet protocol for message exchange among gateway s and router s.

Internet Inter-ORB Protocol (IIOP) Component message passing protocol in CORBA .

Internet Message Access Protocol version 4 (IMAP4) — Protocol that extends Post Office Protocol 3 to enable management and permanent storage and management of e-mail message s on a server .

Internet Protocol (IP) Internet protocol for packet switching and routing.

interpretation Process for translating and executing source code instruction s that interleaves instruction translation and execution.

interpreter Program that performs interpretation .

interrupt Signal to the CPU that some event requires its attention.

interrupt code — Numerically coded value of an interrupt , indicating the type of event that has occurred.

interrupt handler Program or subroutine that is executed in response to an interrupt .

interrupt register Register in the control unit that store s an interrupt code received over the bus or generated by the central processing unit .

intranet — Internal, private network that uses Internet protocols but is only accessible to a limited set of internal users.

I/O — Acronym of input/output.

I/O channel — (1) Device controller dedicated to a mainframe bus port that allows enables many devices to share access to (and the capacity of) the port . (2) Specific hardware component of an IBM mainframe computer system.

I/O port — (1) Communication pathway from the CPU to a peripheral device . (2) Memory address , or a set of contiguous memory addresses, that can be read or written by the CPU and a single peripheral device .

I/O wait state — Idle processor cycle consumed while waiting for data transmission from a secondary storage or input/output ( I/O ) device.

IP — Acronym of Internet Protocol.

IPv6 Internet Protocol standard version 6 that uses 128-bit addresses.

IrDA — Acronym of Infrared Data Association .

ISO — Acronym of International Standards Organization.

iteration — Four to six week period of a system development project that produces a specific set of deliverables including a prototype or the final system.

J2EE — Acronym of Java2 Enterprise Edition .

Java2 Enterprise Edition (J2EE) — Family of standards for developing and deploying component-based distributed applications written in Java .

Java Object-oriented programming language used to construct program s that can be executed on different hardware and system software platforms.

Java server page (JSP) — Server-side component s that generate formatted Web page s using embedded scripts.

Java servlet — Server-side Java program s that can perform complex operations and interact with EJB s and databases.

Java Virtual Machine (JVM) Interpreter that translates and execute s Java program s.

JCL — Acronym of job control language .

job control language (JCL) — Control language used to direct the batch execution of program s or groups of program s.

Joint Photographic Experts Group (JPEG) — (1) Organization that promulgates image representation standards. (2) Standard method of compressed image representation for single images.

journaling — Synonym of transaction logging.

JPEG — Acronym of Joint Photographic Experts Group .

JSP — Acronym of Java server page .

JUMP — Synonym of BRANCH operation.

JVM — Acronym of Java Virtual Machine.

keyboard controller Microprocessor , integrated within a keyboard, that converts keystrokes to coded computer inputs or scan code s.

Kerberos — Security model that defines standard interactions between client s, services, and a security service.

kernel — Portion of the operating system that manages resources and directly interacts with computer hardware.

L1 — Acronym of level one.

L2 — Acronym of level two.

L3 — Acronym of level three.

label — Mnemonic that represents the memory address of a program instruction .

LAN — Acronym of local area network .

large format printer — A printer, typically using inkjet technology, that prints large images such a posters and blueprints.

laser printer — Printer that uses a laser to charge areas of a photoconductive drum and paper.

late binding — Synonym of dynamic linking .

Latin-1 — Standard character coding table containing the ASCII character set in the first 128 table entries and most of the additional character s used by Western European languages in the second 128 table entries.

LCD — Acronym of liquid crystal display .

LDAP — Acronym of Lightweight Directory Access Protocol .

least significant byte Byte within a multiple byte data item that contains the digits of least, or smallest, magnitude.

least significant digit Bit position within a bit string that represents the least, or smallest, magnitude.

level one (L1) cache — Within-CPU cache when all three cache types are used.

level two (L2) cache Primary storage cache implemented within the same chip as a processor .

level three (L3) cache — When three levels of primary storage cache are used, the cache implemented outside the microprocessor .

Lightweight Directory Access Protocol (LDAP) —Internet standard formed from the X.500 standard and adopted by the Internet Engineering Task Force.

line turnaround Signal sent between a sender and receiver that causes them to reverse roles (the sender becomes the receiver and vice versa).

linear address space — Logical view of a secondary storage or I/O device as a sequentially numbered set of storage locations.

linear recording — Recording of data onto a tape in which bit s are placed along parallel track s that run along the entire length of the tape.

Linear Tape Open (LTO) — Proprietary magnetic tape standard developed by Hewlett-Packard, IBM, and Seagate.

link — (1) A type of connection between a directory and another directory or file used to implement a graph directory structure . (2) A pointer that connects two data items within a data structure . (3) An external function call within an object code file.

link editor Program that combines multiple object code modules into an integrated set of executable code with a consistent scheme of memory addresses and references.

link map — Synonym of memory map.

linked list Data structure in which each data item contains a pointer to the previous or next data item.

liquid crystal display (LCD) — Display device that uses liquid crystals that can be changed from transparent to opaque.

little endian — Describes a CPU architecture that store s a multibyte data item with the least significant byte in the storage location with the lowest-numbered address .

load — Copying a word from primary storage to a register .

local area network (LAN) — Network that spans a limited area such as a single building or office floor.

location transparency — Characteristic of software such that resource access is implemented identically whether the resource is part of the local computer system or located within or controlled by a remote computer system.

logic instruction Instruction that implements a boolean comparison operation such as ADD , AND , OR , NOR, or XOR .

logical access — Access to a storage location within a linear address space .

logical record Record formatted and described in terms of a logical (rather than physical) file structure.

logical SHIFT — Shift operation used to extract a single bit from a bit string .

logical topology — Path that message s traverse as they travel among network nodes.

long integer Double precision representation of an integer .

longitudinal redundancy checking (LRC) Parity checking method in which parity bit s are determined based on equivalent bit positions in a group of byte s or character s.

lossless compression Compression algorithm in which data content is unchanged when compressed and then decompressed.

lossy compression Compression algorithm in which data content is altered or lost when compressed and then decompressed.

low order bit — Synonym of least significant digit .

LRC — Acronym of longitudinal redundancy check.

LTO — Acronym of Linear Tape Open .

MAC — Acronym of media access control .

machine data type — Synonym of primitive data type .

machine independence — Synonym of hardware independence .

machine language — Language consisting solely of instruction s from a specific central processing unit instruction set.

machine state — Current processing state of a program or the central processing unit , as represented by the values currently held in register s.

magnetic decay — Loss in strength of a stored magnetic charge over time.

magnetic leakage — Reduction in strength of a stored magnetic charge because of interference from one or more adjacent magnetic charges of opposite polarity.

magnetic tape — Polymer ribbon coated with a metallic compound used to store data.

magneto-optical Secondary storage device that reads and writes data bit s using a combination of magnetic and optical method s.

main memory — (1) Synonym of primary storage . (2) Set of devices that implement primary storage excluding cache .

mainframe — High-capacity computer system designed to support hundreds of interactive users and processes simultaneously.

Mammoth Magnetic tape standard developed by Exabyte based on the Digital Audio Tape standard.

mark sensor — Input device that recognizes printed marks at predetermined locations on an input document.

media access control (MAC) — Set of rules that regulate access to a transmission medium .

megahertz (MHz) — Measurement of wave or clock frequency , one million cycle s per second.

memory — (1) Synonym of primary storage . (2) Random access memory devices used anywhere within a computer system, peripheral device , or device controller .

memory allocation — Allocation of primary storage resources to active processes.

memory map — List of module and data names and memory addresses produced by a link editor.

message — (1) With respect to communication networks, a command, request, or response sent from one network node to another. (2) With respect to component s and object-oriented program s, a request sent from one object or component to another.

method Program within a class that manipulates data.

MFLOPS — Acronym of millions of floating point operations per second .

MHz — Abbreviation of megahertz .

microchip Semiconductor device that implements integrated electronic component s in a single unit.

microcomputer — Computer system that can meet low-intensity processing needs of a single user.

microprocessor Microchip containing all of the component s of a central processing unit .

middleware System software that enables client s and server s or distributed component s to locate and communicate with one another.

midrange computer — Computer system that meets the processing needs of a small- to medium-sized group of interactive users.

MIDI — Acronym of Musical Instrument Digital Interface .

millions of floating point operations per second (MFLOPS) — Measure of processor or computer system speed in terms of the number of floating point computation operations executed per second.

millions of instructions per second (MIPS) — Measure of processor or computer system speed in terms of the number of central processing unit instruction s executed per second.

MIME — Acronym of Multipurpose Internet Mail Extensions .

minicomputer — Computer system that meets the processing needs of a small- to medium-sized group of interactive users.Synonym of midrange computer .

MIPS — Acronym of millions of instructions per second .

modem — Acronym of MOdulator‑ DEModulator.

modulation — Varying the amplitude , frequency , or phase of a carrier wave .

modulator-demodulator (modem) —Device that translates analog signal s into digital signal s (and vice versa), enabling computer hardware to communicate over voice-grade telephone lines.

monitor — (1) Video display device. (2) Hardware or software element that monitor s and reports processing or communication activity.

monochrome — Describes a display device or encoding method that can display or represent only two colors, typically, black and white.

monophonic — Capable of generating only one audible frequency (note) or timbre (voice) at a time.

Moore’s Law — Statement that the transistor density and power of microprocessor s doubles every 18 to 24 months with no per unit cost increase.

most significant byte Byte within a multiple byte data item that contains the digits of most, or largest, magnitude.

most significant digit Bit position within a bit string that represents the most (largest) magnitude.

mouse — Interactive pointing device used to control cursor position and to select object s on a video display.

MOVE Instruction that can copy data bit s among any combination of register s and primary storage locations.

Moving Pictures Experts Group (MPEG) — (1) Organization that promulgates motion video-image representation standards. (2) Method of compressed motion video-image representation.

MP3 — (1) Audio encoding and compression standard. (2) Layer 3 of the MPEG-1 standard.

MPEG — Acronym of Moving Pictures Experts Group .

multicore architecture Microprocessor architecture that embeds multiple CPU s andcache memory on a single chip.

multilevel coding — Describes any method that en code s multiple bit s within each instance of a modulated carrier wave or signal .

multimedia controller Device controller for multiple audio or visual I/O devices.

multimode cable Fiber-optic cable type that surrounds plastic or glass fibers with a reflective coating to contain light.

multinational character Character , such as ñ or é, similar to an English language character but used by Western European languages other than English.

multiple master bus Bus in which more than one attached device may control access to the bus .

multiprocessing — Any CPU architecture in which duplicate CPU s or processor stages can execute in parallel.

Multipurpose Internet Mail Extensions (MIME) — Protocol that enables non-text content to be included in e-mail message s and other Internet data transmissions.

multitasking — Ability of an operating system to support multiple active processes.

multithreaded Process divided into two or more thread s, each of which may be scheduled and executed independently.

multi-CPU architecture — Computer system architecture that employs two or more CPU s on a single motherboard or set of interconnectedmotherboards.

Musical Instrument Digital Interface (MIDI) — Standard method of encoding control information for musical instruments and synthesizers.

n-layer architecture Client-server architecture that uses more than three layers.

n-tiered architecture — Synonym of n-layered architecture.

NAK — Mnemonic of the negative acknowledge ASCII control character .

named pipe Pipe with a name permanently placed in a file system directory that enables communication among processes executing on different computers.

NAS — Acronym of network-attached storage .

native application — Application compiled and linked for a particular central processing unit and operating system .

needs analysis — Synonym of systems analysis .

negative acknowledge (NAK) ASCII control character sent by a receiver to indicate unsuccessful receipt of transmitted data.

network administrator — Manager charged with operating and maintaining a local or wide area network .

network computer Personal computer or workstation with no locally stored operating software, application software , or configuration information.

network interface card (NIC) — Synonym of network interface unit ( NIU ), particularly with respect to a microcomputer , network computer , or workstation .

network interface unit (NIU) — Physical network interface device used by a single computer system.

network layer — Layer of network system software that routes packet s to their destination.

network topology — Structure defined by the organization of network devices, routing of network cabling, and flow of message s through network nodes.

network transparency — Synonym of location transparency .

network-attached storage (NAS) — Architecture in which a dedicated storage server is attached to a general-purpose network to service storage access requests from other server s.

NIC — Acronym of network interface card .

NIU — Acronym of network interface unit .

noise — Combination of electromagnetic interference and distortion that modifies a carrier wave or signal during transmission.

noncontiguous — Any storage allocation scheme under which multiple storage locations allocated to a file or program need not be sequential nor physically adjacent to one another.

nonprocedural language Programming language that describes a processing requirement without describing a specific procedure for satisfying the requirement.

non-volatile [SB5] — Term describing storage devices that retain their contents over long periods of time.

nonvolatile memory (NVM) Memory with long-term or permanent dataretention.

NOT — (1) Boolean operation that generates the value false if its input is true, and true if its input is false. (2) Central processing unit instruction that implements the boolean NOT operation and store s the result in a register or memory .

numeric range — Set of all data values that can be represented by a specific data-encoding method .

NVM — Acronym of nonvolatile memory .

object — One instance, or variable , of a class .

object code — Output of an assembler or compiler that contains machine instruction s and unresolved reference s to external library routines.

object-oriented programming (OOP) — Software construction method or paradigm that configures software as cooperating object s.

Object Request Broker (ORB) CORBA service that maintains a directory of component s and routes message s among them.

objectclass — A Llightweight Ddirectory Aaccess Pprotocol ( LDAP ) concept that defines the attributes common to all members of a class .

OCR — Acronym of optical character recognition .

octal notation Base 8 numbering system that uses digit values ranging from 0 to 7.

odd parity — Error-detection method that appends a parity bit to each transmitted or stored character . The value of the parity bit is zero if the number of one-valued bit s in a character is odd, and one otherwise.

offset register Register that holds a memory address offset, which is added to each explicit memory reference.

on-off keying (OOK) — Synonym of pulse code modulation .

OOK — Acronym of on-off keying .

OOP — Acronym of object-oriented programming .

op code — Synonym of operation code .

Open Systems Interconnection (OSI) model — Standardized seven layer architecture for computer network software and hardware.

operand Component field of an instruction containing a data value or address used as input to or output from a specific processing operation.

operating expenditure — Funds expended during the current operating period to support normal operations.

operating system — Set of software program s that manage and control access to computer resources.

operation code — Coded value or bit string representing the function or operation to be performed by a processor .

optical character recognition (OCR) Method s, program s, and devices by which printed character s are recognized as computer system input or data.

optical scanner — Device that can scan printed graphic inputs and convert them to computer system input or data.

OR — (1) Boolean operation that generates the value true if either or both of its inputs are true. (2) Central processing unit instruction that generates the value true if either or both of its inputs are true.

ORB — Acronym of Object Request Broker.

OSI — Acronym of Open Systems Interconnection.

overflow — Error condition that occurs when the output bit string of a processing operation is too large to fit in the designated register .

packet — Fundamental unit of data communication in a computer network .

packet switching — Form of time division multiplexing in which multiple message streams are broken into packet s and individually transmitted and routed to their destination.

packet-filtering firewall Firewall that examines each packet and matches header content to a list of allowed or denied packet types.

page — Small fixed-size portion of a program , swapped between primary and secondary storage under virtual memory management .

page fault Condition that occurs under virtual memory management when a program references a memory location in a page not currently held in primary storage .

page frame — Portion of primary storage designated to hold a page under virtual memory management .

page file — Synonym of swap space or swap file .

page hit — Reference to a page held in memory under virtual memory management .

page table — Table of page s and information about them maintained by an operating system that implements virtual memory management .

palette — Set or table of colors used by a video display device or controller.

parallel access — Simultaneous access to multiple portions of a data item through multiple communication channel s or transmission media.

parallel transmission — Simultaneous transmission of multiple parts of a single message over multiple transmission media or channel s.

parent process Process that initiates and controls the execution of another (child) process .

parity bit Bit appended to a small data unit, such as an ASCII character , that store s redundant information used for error checking. See even parity and odd parity .

parity checking — Act of validating data by recomputing the value of a parity bit .

passive matrix display Liquid crystal display that shares transistor s among rows and columns of pixel s.

PC — Acronym of personal computer .

PCB — Acronym of process control block .

PCM — Acronym of pulse code modulation .

PDF – Acronym of Portable Document Format .

peer-to-peer bus Bus in which more than one attached device may control access to the bus .

peer-to-peer communication protocol — Protocol that enables processes to communicate synchronously across a network.

peripheral device — Device on a system bus other than the central processing unit and primary storage .

peripheral processing unit — Synonym of I/O channel , particularly as applied to minicomputer s and mainframe s not manufactured by IBM.

personal computer (PC) — Synonym of microcomputer .

phase — Characteristic of an analog wave that indicates its current cycle position (in degrees) with respect to the cycle origin.

phase shift keying (PSK) — Synonym of phase shift modulation .

phase shift modulation — Data transmission method that en code s data values as variations in carrier wave phase .

phoneme — Individual vocal sound comprising a primitive component of human speech.

photosensor — Device that generates an electrical signal when light is shone upon it.

physical layer — Layer of network system software responsible for physical transmission of signal s representing data.

physical memory — Physical primary storage capacity of a computer system, in contrast to virtual memory capacity and addressable memory .

physical record — Unit of physical data transfer to or from a storage device.

physical topology — Physical placement of cables and connections in a network topology .

pipe — Region of shared memory through which multiple processes executing on the same machine can exchange data.Shared memory region used to send the data output of one process to another process as input.

pipelining Method of organizing CPU circuitry to enable multiple instruction s to be in different stages of execution at the same time.

pixel — (1) Abbreviation of the term “picture element.” (2) Single unit of data in a graphic image. (3) Single point on a display surface.

plasma display — Display that generates light by applying an electrical charge to neon gas.

platter — One disk within a disk storage device, the surface or surfaces of which store data.

plotter — (1) Device that generates printed output through the movement of paper and one or more pens. (2) An ink jet printer that can print wide sheets or rolls of paper. (3) Synonym of large format printer .

point — (1) One seventy-second of an inch. (2) Measurement unit for font size.

pointer — (1) Data element that contains the address (location in a storage device) of another data element. (2) Device used to input positional data or control the location of a cursor .

polymer memory — Type of nonvolatile memory that store s bit values in plastic with electrical resistance that can be increased or decreased by an electrical field .

polyphonic — Capable of generating many audible frequencies (notes) or timbres (voices) simultaneously.

pop Process of removing an item from the top of a stack and copying its content to processor register s.

POP3 — Acronym of Post Office Protocol version 3 .

port — Physical connection point on a bus , communication channel , or input/output device identified by a unique integer number.

Portable Document Format (PDF) — An image description language (a superset of PostScript ) developed by Adobe Systems Incorporated.

Post Office Protocol version 3 (POP3) — Protocol that standardizes the interaction between e-mail client s and server s.

PostScript — Language for representing and transmitting complex images and display contents.

power sag — Momentary reduction in the voltage or amperage of electrical power.

power surge — Momentary increase in the voltage or amperage of electrical power.

preemptive scheduling Scheduling method that allows enables a higher-priority process to interrupt and suspend a lower-priority process .

presentation layer — Layer of network system software responsible for input and output to network nodes.

primary storage — High-speed storage within a computer system, accessed directly by the central processing unit , used to hold currently active program s and data immediately needed by those program s.

primitive data type Integer , real number , character , Boolean, memory address , and double precision data types supported by a central processing unit .

priority-based scheduling Scheduling method that determines which ready thread or process should be dispatched to the central processing unit based on user or process priority.

procedure — Group of instruction s that are always executed as a unit (similar to a function or subroutine ).

process — (1) Program or program fragment that is separately managed and scheduled by the operating system . (2) To transform input data by the application of processing operations. (3) Representation of data or information processing on a data flow diagram.

process control block (PCB) Data structure that contains information about a currently active process .

process family Parent process and all its descendants.

process list — Synonym of process queue.

process queue Data structure containing process control block s for all current processes.

processor — Any device capable of performing data transformation operations.

production version Program that contains no debugging information and has been optimized for minimal consumption of hardware resources.

program — Sequence of processing instruction s.

program counter — Synonym of instruction pointer .

program editor — Software that assists programmer s in creating valid source code .

program profiler — Software utility that monitor s and reports the activities and resource utilization of another program during execution.

program status word (PSW) Bit string held in a control unit register that store s status information ( flag s) in each bit .

program translator Program that translates instruction s in one programming language or instruction set into equivalent instruction s in another programming language or instruction set. See assembler , compiler , and interpreter .

programmer — Per son who creates or maintains program s.

programmer’s workbench — Integrated set of program s that support program creation, editing, translation, and debugging.

programming language — Any language in which computer-processing function s or instruction s can be expressed.

protocol stack — Set of software program s, services, or device drivers, each of which implements one protocol in a layered set of protocols.

PSK — Acronym of phase shift keying.

PSW — Acronym of program status word .

pulse code modulation (PCM) Signal coding method under which bit values are represented as bursts of light or electrical voltage.

push Process of copying register values to the top of a stack .

quality of service — Guaranteed minimum data transfer throughput between a sender and receiver.

quantum measurement problem — Behavior where the multiple states of a qubit are disturbed by any attempt to measure their value.

QIC — Acronym of Quarter Inch Committee .

Quarter Inch Committee (QIC) — Committee that promulgates standards for cartridge magnetic tape s.

qubit — Data stored in a single quantum particle.

radio frequency (RF) — Electromagnetic radiation propagated through space.

radix Base of the numbering system, such as 2 for the binary numbering system and 10 for the decimal numbering system.

radix point — Period or comma that separates the whole and fractional parts of a numeric value.

RAID — Acronym of Redundant Array of Inexpensive Disks .

RAM — Acronym of random access memory .

random access — Ability of a storage device to access storage locations directly, or in any desired order.

random access memory (RAM) — (1) Generic description of semiconductor devices used to implement primary storage . (2) Device used to implement primary storage that provides direct access to stored data.

raw data transfer rate — Number of bit s per time interval that can be sent through a communication channel .

read-only memory (ROM) Primary storage device that can be read but not written.

read/write head — Mechanism within a storage device that reads and writes data to/from the storage medium .

read/write mechanism — Synonym of read/ write head.

ready state — State of an active process or thread that is waiting only for access to the central processing unit .

real number — Number that can contain both whole and fractional component s.

real resource — Hardware or software resource that physically exists.

real-time scheduling — Any scheduling method that guarantees the complete execution of a program or program cycle within a stated time interval.

record — (1) Data structure composed of data items relating to a single entity such as a per son or transaction . (2) Unit of data transfer. (3) Primary component data structure of a file.

recording density — Closeness or spacing of bit positions on a storage medium , typically as measured in bit s, byte s, or track s per inchSynonym of areal density .

Reduced Instruction Set Computing (RISC) — (1) Use of a small set of simple central processing unit instruction s that cannot be decomposed into other processor instruction s. (2) Processor architecture that emphasizes short, primitive instruction s that reference operand s contained in register s, in contrast to complex instruction set computing.

Redundant Array of Inexpensive Disks (RAID) — Set of techniques for improving storage device performance or ensuring data integrity using redundant multiple disk storage devices.

refresh cycle — (1) Period during a dynamic random access memory refresh operation when the storage device is unable to respond to a read or write request. (2) Transfer of one full screen of data to a video monitor .

refresh rate — Number of times per second a refresh operation occurs on a video display device.

register — High-speed storage location within a central processing unit that can hold a single word .

relative addressing — Synonym of indirect addressing .

relative path — Path that begins at the level of the current directory .

remote procedure call (RPC) — Protocol that enables a process on one computer to call a process on another computer.

repeater — (1) Device that relays signal s from one network segment to another. (2) Synonym of bridge .

request for proposal (RFP) — Formal document stating hardware or software requirements and requesting proposals from vendors to meet those requirements.

requirements analysisdiscipline — Synonym of systems analysisActivities of the Unified Process that develop models of system requirements.

requirements document — Output produced by systems analysis .

resistance — Phenomenon in energy wave transmission where energy is converted from one form to another, for example, electrical energy to heat.

resolution — Number of pixel s displayed per linear measurement unit.

resource availability model — A model of the computing resources that can be provided by a given combination of computer hardware and system software .

resource registry — Database of services and resources available within a local or wide area network .

return Instruction executed at the end of a function , subroutine , or procedure to return control to the calling function , subroutine , or procedure .

return wire — Transmission line that completes an electrical circuit between the sending and the receiving device.

RF — Acronym of radio frequency .

RFP — Acronym of request for proposal .

RGB — Acronym of rRed, gGreen, and bBlue.

ring topology — Network configuration in which each network node is connected to two other network nodes, with the entire set of connections and nodes forming a closed ring.

RIP — Acronym of Routing Information Protocol .

RISC — Acronym of Reduced Instruction Set Computing .

Rock’s Law — Observation that states that the cost of fabrication facilities for the latest generation of semiconductor devices doubles every four years.

ROM — Acronym of read-only memory .

rotational delay — Waiting time for the desired sector of a disk to rotate beneath a read/write head .

router — Device that examines packet destination addresses and forwards them to another network segment, if necessary.

Routing Information Protocol (RIP) Internet protocol for the exchange of routing information among network nodes.

routing table — Table of network node addresses and transmission lines or connection port s.

RPC — Acronym of remote procedure call .

run queue — Synonym of thread list.

running state — State of a process or thread that currently is executing within the central processing unit .

sampling — (1) Process of measuring and digitally encoding one or more parameters of an analog signal at regular time intervals. (2) Process of digitally encoding analog sound waves.

SAN — Acronym of storage area network .

sandbox — Protected area of a program within which a Java applet is executed.

SAS — Acronym of serial-attached SCSI .

SATA — Acronym of serial ATA .

scaling up — Increasing available processing and other computer system power by using ever larger and more powerful computers.

scaling out — Increasing available processing and other computer system power by partitioning processing and other tasks among multiple computer systems.

scan code — Coded output generated by a keyboard for interpretation by a processor or keyboard controller .

scanning laser — Laser that is automatically swept back and forth over a predefined viewing area, as used in devices such as bar code readers.

scheduler Program within the operating system that controls process states and access to the CPU .

scheduling Process of determining and implementing process priorities for access to hardware resources.

scripting language — (1) Simple programming language that can be embedded within HTML page s. (2) Stored set of operating system commands or a job control language program .

SCSI — Acronym of Small Computer System Interface .

SDLC — Acronym of systems development life cycle .

SDRAM — Acronym of synchronous dynamic random access memory .

second-generation language (2GL) — Synonym of assembly language .

secondary storage — Set of computer system devices that provide large-capacity and long-term data storage.

sector — (1) Smallest accessible unit of a disk drive. (2) For most disk drives, 512 byte s.

secure shell (SSH) — Modern variant of Telnet that encrypts data flowing between client and server .

segment register Register that holds the base address of a memory segment, as used in a central processing unit that uses a segmented memory model .

segmented memory model Memory allocation and partitioning based on equal sized segments and segmented memory addresses.

semiconductor — Material with resistance properties that can be tailored between those of a conductor and an insulator by adding chemical impurities.

sequential access time — Time required to access the second of a stored sequential pair of data items.

serial access — Access technique where data items are read and written in an order corresponding to their position within allocated storage locations.

serial ATA (SATA) — Storage device and cabling standard, compatible with older parallel ATA standards, butusingserial transmission.

serial transmission — Transmission method in which individual bit s are transmitted sequentially over a single communication channel .

serial-attached SCSI (SAS) — Storage device and cabling standard, compatible with older parallel SCSI standards, but using serial transmission .

server — Computer system or process that manages hardware or software resources and makes those resources available to client s.

service call — Request for an operating system service by an application program .

service layer — Portion of the operating system that accepts service call s and translates them into low-level requests to the kernel .

service-oriented resource access Operating system architectural or behavioral feature in which all resources are managed and accessed through server processes.

service standard — Standard for interacting with a shared resource.

session layer — Layer of network system software responsible for establishing and managing communication sessions.

shell — User interface (or command layer ) of an operating system .

SHIFT — Operation whereby bit s of a bit string are moved left or right by a stated number of positions, empty positions are filled with zeros, and bit values that shift beyond the bounds of the bit string are discarded.

shortcut — Synonym of link , as implemented within Microsoft Windows for graph directory structure s.

shortest time remaining Scheduling method that assigns highest priority to processes or requests with shortest time remaining until completion.

sibling process — Another child process created, or spawned, by the same parent.

signal — (1) Specific data transmission event or group of events that represents a bit or group of bit s. (2) Message sent from one active process to another.[SB6]

signal-to-noise (S/N) ratio — Mathematical relationship between the power of a carrier signal and the power of the noise in the communication channel , measured in decibels.

signal wire Component of an electrical communication channel (circuit) used to transmit a carrier wave or signal .

SIMM — Acronym of single in-line memory module .

Simple Mail Transport Protocol (SMTP) — Earliest e-mail protocol that defines how text message s are routed through the Internet .

Simple Object Access Protocol — Standard for distributed object interaction.

simplex — Type of communication channel that enables transmission in only one direction.

sine wave — Waveform that varies continually between positive and negative states.

single in-line memory module (SIMM) — Small printed circuit board with memory chips on one or both sides and electrical contacts on one edge.

single-mode cable — Highest quality optical cable constructed so that light waves travel down the center of the fiber.

singly linked list Data structure in which each data item contains a pointer to the next data item.

skew — Timing differences in the arrival of signal s transmitted simultaneously on parallel communication channel s.

Small Computer System Interface (SCSI) — Family of standard buses designed primarily for connecting secondary storage devices.

SMTP — Acronym of Simple Mail Transport Protocol .

S/N — Acronym of signal-to-noise.

SOAP — Acronym of Simple Object Access Protocol .

socket Internet standard for service identification that combines an Internet address with a service port number, such as

software monitor Program that monitor s and reports the utilization of a software resource.

son — File containing the results of updating a master file (the father ) based on the contents of a transaction file.

sound card — Hardware device containing component s for sound input and output.

source code Instruction s or statements in a high-level programming language .

spawn — Creation of a child process by a parent process .

speaker dependent Speech recognition system that recognizes input from only one user and that must be trained to accurately recognize that user’s specific speech patterns.

special-purpose processor — (1) Processor with a limited set of processing function s. (2) Processor capable of executing only a single program .

speculative execution — Executing instruction s after branch prediction but before the final branch condition value is known with certainty.

speech recognition Process of recognizing human speech as computer system input.

speech synthesis Process of generating human speech based on character or textual input.

SRAM — Acronym of static random access memory .

SSH — Acronym of secure shell .

stack — (1) List of data items maintained in last-in, first-out order. (2) Set of register s or memory locations used to store the register values of temporarily suspended processes.

stack overflow Condition that occurs when an attempt is made to add data to a stack that is already at its maximum capacity.

stack pointer Register containing the primary storage address of the last (most recently added) stack element.

star topology — Physical network connection pattern in which all nodes are attached to a central node.

start bit — Zero bit s that are added to the beginning of each character in asynchronous serial data transmission.

stateful firewall Firewall that track s the progress of complex client-server interactions.

static connection — Mapping between a local resource name and a remote resource that does not change once initialized and that must be explicitly initialized prior to use.

static linking — Linking process in which library and other subroutine s cannot be changed once they are inserted into the executable code .

static random access memory (SRAM) — Type of random access memory that implements bit storage with a flip-flop circuit.

storage allocation table — Table that correlates storage device allocation unit s with specific files, directories, or unallocated space.

storage area network (SAN) — High speed interconnection among general-purpose server s and a separate storage server .

storage input/output control layer System software layer that controls input and output to and from storage devices.

storage medium — Device or substance within a storage device that physically store s data.

store — Operation in which register content is copied to a memory location.

store and forward — Interconnected system of end nodes and transfer point s used to route data among end nodes.

strategic plan — Long-range plan stating the services to be provided by an organization and the means for obtaining and using needed resources.

string — Ordered set of related data elements, usually stored as a list or an array .

subroutine — Named segment of a high-level language program that is always executed as a unit.

subtractive colors — Cyan (absence of red), magenta (absence of green), and yellow (absence of blue).

supercomputer — Computer designed for very fast processing of real number s, typically implemented with some form of parallel processing.

supervisor Operating system program that serves as the master interrupt handler.

surge protector — Hardware device that controls electrical power surge s.

sustained data transfer rate — Maximum data transfer rate that can be sustained by a device or a communication channel during lengthy data-transfer operations.

swap file — Synonym of swap space or page file.

swap space — Area of secondary storage used to hold virtual memory page s that cannot fit into primary storage .

switch — (1) Device that exists in one of two states and can be instructed to alternate between them. (2) Network node that quickly routes packet s among network segments with switching technology.

symbol table — List of program module and data names and their allocated primary storage locations.

symbolic debugger — Debugger that can report program execution progress and errors in terms of symbolic module and data names used within program source code .

synchronous dynamic random access memory (SDRAM) — Read-ahead random access memory that breaks read and write operations into a series of simple steps that can be completed in one bus clock cycle .

synchronous idle message — Control message sent continually between sender and receiver to keep their internal clocks synchronized.

synchronous transmission — Reliable high-speed method of data transmission in which data are sent in continuous data streams.

system administration — Managerial actions required to ensure efficient, reliable, and secure computer system operation.

system bus Bus shared by most or all devices in a computer system.

system development tools — (1) Software tool designed to aid in creating groups of program s constituting an entire system. (2) Approximate synonym of computer assisted software engineering tool.

system overhead — Resource(s) consumed for resource allocation and translation function s.

system requirements model — Model that provides the detail necessary to develop a system that meets the needs the user requires.

system software — Software program s that perform hardware interface, resource management, or application support function s.

systems analysis Process of ascertaining and documenting information-processing requirements.

systems analyst — Per son who performs systems analysisbusiness modeling and requirements discipline activities.

systems architecture — Structure, interaction, and technology of computer system component s.

systems design Process of determining the exact configuration of all hardware and software component s in an information system.

systems designer — Per son who performs systems design discipline activities.

systems development life cycle (SDLC) Process to for developing an information system using survey, analysis, design, implementation, and evaluationfollowing a methodology or series of steps or activities such as the Unified Process .

systems implementation Process of software construction, installation, and testing on a given hardware configuration.

systems programmer — Per son who creates or maintains systems software.

systems survey Process of initially ascertaining user processing requirements and determining the feasibility of meeting those requirements with computer-based solutions.

tape drive — Device that contains motors that wind and unwind tapes and read/write head s to access their content.

target channel adapter — Interface or controller that connects a device that can only respond to data transfer commands to an Infiniband or Fibre Channel network.

TCA — Acronym of target channel adapter .

TCB — Acronym of thread control block .

TCP — Acronym of Transmission Control Protocol .

TCP/IP — Acronym of Transmission Control Protocol/Internet Protocol.

TDM — Acronym of time division multiplexing .

Telnet — Protocol in which users on one Internet host can interact with another host’s operating system command layer .

terminal — Synonym of video display terminal ( VDT ).

testing discipline — Activities of the Unified Process that verify correct functioning of infrastructure and application software component s and ensure that they satisfy system requirements.

TFT – Acronym of thin-film transistor .

thin client — A synonym of network computer .

thin-film transistor Transistor embedded within a device such as a display surface and constructed using semiconductor fabrication technology.

thread — Subcomponent of a process that can be independently scheduled and executed.

thread control block (TCB) Data structure in which an operating system keeps track of thread-specific information.

thread cycle — Set of program instruction s that can be executed repetitively.

thread list — Set of thread s awaiting execution represented by a list of thread control block s.

three-layer architecture Client-server architecture composed of three layers: the view layer , the business logic layer , and the data layer .

three-tier architecture — Synonym of three-layer architecture .

third-generation language (3GL) — High-level programming language that does not possess advanced capabilities for interactive input/output, database processing, or nonprocedural programming.

time division multiplexing (TDM) — Technique that subdivides the capacity of a communication channel into discrete time slices, each of which may be allocated to a separate sender and receiver.

timer interrupt Interrupt automatically generated by the central processing unit in response to the passage of a specific interval.

token — Control packet that regulates access to a communication channel .

token passing — Media access protocol that uses token s passed among network nodes.

trace — Connection within a microchip or printed circuit board that enables electrons to travel from one place to another.

track — Set of sector s on one side of a disk platter that form a concentric circle.

track-to-track seek time — Time required to move a disk read/write head between two adjacent track s.

transaction — (1) Event or system input that initiates the execution of one or more program segments. (2) Real-world event from which data input is derived, such as a sale. (3) A general term describing any change to stored data, such as the addition of a record to a file.

transaction logging Method of file system update in which all changes to file and directory content also are written immediately to a separate log, or journal, which is used to recover lost data in the event of a system crash.

transistor — Solid state electrical switch that forms the basic component of most computer- processing circuitry.

Transmission Control Protocol (TCP) Internet protocol for translating message s into packet s and guaranteeing their delivery.

transmission medium — Physical communication path through which a carrier wave is propagated.

transport layer — Layer of network system software responsible for converting network message s into packet s or other data structure s suitable for transmission.

tree directory structure — Synonym of hierarchical directory structure .

truncation — Act of deleting bit s that will not fit within a storage location.

twin-axial cable Transmission medium composed of two wire strands surrounded by an insulator, a braided return wire , and a tough outer coating.

twisted pair wire Transmission medium consisting of two electrical conductor s ( wire s) twisted around one another.

two’s complement — Notation system that represents positive integer s as an ordinary bit string , and negative integer s by adding one to the bit string that represents the absolute value.

Type I error — (1) Percentage of data items containing errors that will be incorrectly identified as error free. (2) Percentage of a sample or population that will be incorrectly identified as satisfying the null hypothesis.

Type II error — (1) Percentage of data items without errors that will be incorrectly identified as containing errors. (2) Percentage of a sample or population that will be incorrectly identified as not satisfying the null hypothesis.

unblocked — Storage of a single logical record within a physical record ( block ).

unconditional BRANCH — Synonym for BRANCH instruction .

undelete operation — Act of restoring a record or file by re-creating its index information ( directory entry) and recovering its previously allocated storage locations.

underflow — (1) Condition that occurs when a value is too small to represent in floating point notation . (2) Overflow of a negative exponent in floating point notation .

Unicode — Standard 16-bit character coding method .

Unified Process (UP) — Iterative system development life cycle based on object-oriented techniques.

Uniform Resource Locator (URL) — Unique name that identifies a Web resource and is composed of a protocol, host, port , and resource.

uninterruptible power supply (UPS) — Device that provides electrical power when normal power inputs are interrupted.

unresolved reference — Synonym of external function call .

unsigned integer — Data type which store s positive integer values as ordinary binary numbers.

UP — Acronym of Unified Process .

UPS — Acronym of uninterruptible power supply .

URL — Acronym of Uniform Resource Locator .

utility program Program that performs a commonly used function , such as printing a text file or copying a file, typically provided by the operating system either as separate tool or as part of the service layer .

variable — (1) Mnemonic that represents a data item memory address in assembly language . (2) Name that represents a data item memory address in a high-level programming language .

variable length instruction — One instruction from a set of central processing unit instruction formats that vary in length.

VC — Acronym of virtual circuit .

VDT — Acronym of video display terminal .

vector — (1) Line segment that has direction and length. (2) One-dimensional array .

vector list — List of line descriptions used for the input or output of graphic images.

versioning —Process that archives original file versions as they are modified.

vertical redundancy checking — Synonym of parity checking .

victim Memory page chosen to be swapped to secondary storage under virtual memory management .

video controller — Device connected to the system bus and a video monitor that accepts input from the CPU or main memory and generates output appropriate to the video monitor .

video display terminal (VDT) — Input/output device comprising a keyboard, video display surface, and one or more communication port s.

video random access memory — Specific random access memory type used within a video controller (usually dual ported).

view layer — Division of the client-server architecture that accepts user input and formats and displays processing results.

virtual circuit (VC) — Transmission path established between sender and receiver before data is transmitted.

virtual local area network — Two shorter local area network s joined by a bridge , also called a bridged local area network .

virtual memory management — Mode of operating system memory management in which secondary storage is used to extend the capacity of primary storage .

virtual resource — Resource visible to a user or program , but not necessarily available at all times or physically extant.

virus Program or program fragment that infects a computer by permanently installing itself, performs one or more malicious acts on the infected computer, and replicates and spreads itself using services of the infected computer.

volatile — Storage devices that cannot retain their contents indefinitely.

voice over Internet Protocol (VoIP) — Family of technologies and standards that enables voice message s and data to be carried over a single packet-switched network.

VoIP – Acronym of voice over Internet Protocol .

volatility — (1) Rate of change in a set of data items. (2) Lack of ability to permanently store data content.

VRAM — Acronym of video random access memory .

wait state — Idle processor cycle consumed while waiting for a response from another device.

WAN — Acronym of wide area network .

wavelength-division multiplexing (WDM) — Form of frequencydivision multiplexing that simultaneously transmits multiple message s over a fiber-optic cable .

WDM — Acronym of wavelength-division multiplexing .

Web — Synonym of World Wide Web ( WWW ).

wide area network (WAN) — Network that spans large physical distances, such as multiple buildings, cities, regions, or continents.

wire — Connection that allows enables electrons to travel from one place to another.

wiring concentrator — Simplest form of a hub that concentrates wiring connections at a single point .

word — Unit of data processed by a single central processing unit ( CPU ) instruction .

working directory — Synonym of current directory .

workload model — Synonym of application demand model.

workstation — (1) Powerful microcomputer designed to support demanding numerical or graphical processing tasks. (2) A synonym of personal computer or microcomputer .

World Wide Web (WWW) — Collection of resources accessed over the Internet by standard protocols such as FTP and HTTP .

WORM — Acronym of write once read many .

write once read many (WORM) — Type of optical storage media that is manufactured blank and can be written to once.

WWW — Acronym of World Wide Web .

XML — Acronym of eXtensible Markup Language.

XOR — Acronym of eXclusive OR .