Macmillan Dictionary of Personal Computing & Communications

400 Pages·1986·63.72 MB·English

by  Dennis Longley, Michael Shain (auth.)

MACMILLAN
DICTIONARY
OF
PERSONAL
COMPUTING&
COMMUNICATIONS
MACMILLAN
DICTIONARY
OF
PERSONAL
COMPUTING&
COMMUNICATIONS
Dennis Longley
Michael Shain
M
MACMILLAN
REFERENCE
BOOKS
© The Macmillan Press Ltd, 1986
Softcover reprint ofthe hardcover 1st edition 1986978-0-333-39083-2
All rights reserved. No reproduction, copy or transmission of this
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be liable to criminal prosecution and civil claims for damages.
First published 1986 by
THE MACMILLAN PRESS LID
London and Basingstoke
Associated companies in Auckland, Delhi, Dublin, Gaborone,
Hamburg, Harare, Hong Kong, Johannesbur~, Kuala Lumpur,
Lagos, Manzini, Melbourne, Mexico City, Narrobi, New York,
Singapore, Tokyo.
British Library Cataloguing in Publication Data
Longley, Dennis
Macmillan dictionary of personal computing
and communications.
1. Microcomputers - Dictionaries
I. Title 11. Shain, Michael
OO~.16'03'21 QA7 6.5
ISBN 978-0-333-42170-3 ISBN 978-1-349-18341-8 (eBook)
DOI 10.1007/978-1-349-18341-8
The paperback edition of this book is sold subject to the condition
that It shall not, by way of trade of otherwise, be lent, resold, hired
out, or otherwise circulated without the publisher's prior consent
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published and without a similar condition including this condition
being imposed on the subsequent purchaser.
A
abbreviated addressing In programming, a absolute loader In programming, a routine
process that enables a user to employ an that reads a computer program into main
address having fewer characters than the full memory, beginning at the assembled origin.
address. lt provides a faster me ans of pro- See ASSEMBLING, LOADER , MAIN MEMORY.
cessing data because the shorter address
requires less time to decode. See ADDRESS- absolute value In mathematics, the value of
ING. a number regardless of a prefixed plus or
minus sign, i.e. the absolute value of -5 is 5.
ABEND In operations , an ABnormal END
abstract data type In data structures, a
of a task prior to its completion on a
data type that is defined solely in terms of
mainframe because of an error. A micro-
the operations that can be performed on
computer in emulation mode should be
objects of that type and the range of values
programmed to handle this in a controlled
that it can take, without regard to the
manner. See TERMINAL EMULATION .
method of representation of the value. See
TYPE.
abort In operations, to terminate, in a
controlled manner, a processing activity in a AC See ACCUMULATOR, ALTERNATING
computer system because it is impossible or
CURRENT.
undesirable for the activity to proceed.
ACC See ACCUMULATOR.
abscissa In mathematics, the horizontal
axis of a coordinate graph. Compare acceleration potential In electronics, the
ORDINATE. See CARTESIAN COORDINATES, co- voltage between the cathode and the face of
ORDINATE GRAPH. the tube which attracts the beam of focused
electrons, causing them to impinge on the
phosphor dots. See CRT, PHOSPHOR DOTS.
absolute address In programming, (1) an
address in a computer language that identi- acceptance testing In operations, aseries of
fies a storage location or a device without tests designed to demonstrate the functional
the use of any intermediate reference, (2) an capabilities of a new computer system. lt is
address that is permanently assigned by the usually conducted by the manufacturer to
machine designer to a storage location, (3) a show the customer that the system is in
pattern of characters that identifies a unique working order.
storage location or device without further
modification. See ADDRESS. ACCESS US Army Automated Catalog of
Computer Equipment and Software
Systems.
absolute assembler In programming, a
specific type of assembly language program access In programming, the manner in
designed to produce binary programs con- which files or data sets are referred to by the
taining only absolute addresses and address computer. See DIRECT ACCESS, RANDOM
references. See ABSOLUTE ADDRESS, ASSEM-
ACCESS, SEQUENTIAL ACCESS.
BLING.
access arm In backing storage, a mech-
absolute code In programming, a code that anical device in a disk drive that positions
uses computer instructions with absolute the reading and writing mechanisms. See
addresses. See ABSOLUTE ADDRESS. DISK DRIVE, HEAD.
2 access barred
access barred In data communications, a accidental destruction In data security, the
data faciJity that permits a terminal instal- unintentional overwriting or deletion of
lation to make outgoing, or receive incom- data, e.g. by faulty hardware or software.
ing, calls but not both. Backup is needed for recovery. See BACKUP
COPY.
access control (1) In computer networks,
the control of system usage, imposed by accordion fold In pnntmg, a method of
hardware, software and administrative con- folding paper in which each fold is in the
trols. Such controls include system monitor- opposite direction to the previous one. A
ing, user identification, ensuring data in- printer can be fed with accordion-folded
tegrity, recording system access and changes paper without continuous operator inter-
and methods for granting user access. See vention.
HARDWARE, SOFTWARE. (2) In databases, the
control of the use of the database accumulator In architecture, a device that
information. Access to a particular user may functions as a holding register for arithmetic,
be restricted both in terms of the data items logical and input/output operations. In some
that may be made available and the CPUs, data words fetched from memory are
operations that may be performed on it, e.g. loaded into the accumulator and words to be
read, upqate etc. stored into memory are first loaded into this
register. See CPU, INPUT/OUTPUT, REGISTER.
access line In data communications, a tele-
communication line that continuously con- accuracy In mathematics, the degree of
nects a remote station to a DSE. A tele- exactness of an approximation or measure-
phone number is associated with such lines. ment. It denotes the absolute quaJity of the
See DSE. result with respect to its true value, as
compared with precision which is concerned
access time In backing storage, the time with the amount of detail used in specifying
interval between the instant that data is a result. Thus a two-digit result may be more
requested from the storage device to the accurate than an incorrect three-digit result,
instant that it is delivered to the CPU, and but it will be less precise. See PRECISION.
vice versa. The average access time for
Aces In computer languages, a continuous
magnetic disk systems is usually based upon
simulation language. See CONTINUOUS SIMU-
the assumption that the read/write heads will
LATION.
have to move over one-third of the maxi-
mum number of tracks in a random seek achromatic color In computer graphics, an
operation. Compare SEEKS PER HOUR. See intermediate gray level in the monochro-
CPU, MAGNETIC DISK, READ/WRITE HEAD, matic gray scale. See GRAY SCALE.
TRACK.
AC IA See ASYNCHRONOUS COMMUNICA-
TIONS INTERFACE ADAPTOR.
~-+--+--+---+---+--1" ACK See ACKNOWLEDGE CHARACTER.
acknowledge character In data com-
0.0001
munications, a character transmitted by a
station as an affirmative response to the
station with wh ich the connection has been
set up. Compare NEGATIVE ACKNOWLEDGE-
MENT. See ACKNOWLEDGEMENT, STATION.
acknowledgement In data communica-
tions, the transmission by a receiver of
....a ge .'.ccess Time
SIMICond: T Ifi81Of1: B I);"ioo: M milion acknowledge characters as a response to a
access time sender. See AFFIRMATIVE ACKNOWLEDGE-
Memory cost/performance trade off. MENT, NEGATIVE ACKNOWLEDGEMENT.
Ada 3
ACKO See AFFIRMATIVE ACKNOWLEDGE- activity loading In data processing, a
MENT. method of storing records on a file in which
the most frequently processed records can
ACKI See AFFIRMATIVE ACKNOWLEDGE- be located most readily. See RECORD.
MENT.
activity ratio In data processing, the ratio
of the number of records in a file that are in
ACM See ASSOCIATION FOR COMPUTING
use to the total number of records in that
MACHINERY.
file. See RECORD.
acoustic coupler In data communications, a
ACTSU US Association of Computer
device to interface an item of equipment,
Time Sharing Users.
producing digital signals, to a telephone
network. Sound transducers in the acoustic
aetual data transfer rate In data com-
coupler produce sound tones corresponding
munications, the average number of bits,
to the digital signals; a telephone handset is
characters or blocks, per unit time, trans-
placed in contact with the sound transducers
ferred from a data source and received by a
so that these tones can be input into the
data sink. See DATA SINK, SOURCE.
telephone network. See MODEM, TRANS-
DUCER. aetuator In hardware, a device that is
capable of mechanical action under the
action message In operations, a message control of a signal. See INDUSTRIAL ROBOTS.
issued because of a condition that requires
an operator response. ACU See AUTOMATIC CALLING UNIT.
activation In computer networks, the Ada A trademark, in programming, a
process by which a component of anode is language named after Augusta Ada, Coun-
made ready to perform the functions for tess of Lovelace who assisted Babbage.
which it was designed. See NODE. (a) Main applications. Ada was developed
for use in computer control and communica-
aetive device In e1ectronics, a circuit that tion systems, where instruments or systems
contains an amplifier providing gain. Com- are monitored or governed by a program.
pare PASSIVE DEVICE. See AMPLIFIER, GAIN. Typical uses include factory production
lines, data recording in laboratories, naviga-
ti on al systems, networking and interfacing
active file In data structures, a permanent
of multiple processors. Ada is aimed at
or temporary file, having an expiration date
installations with a long lifespan where
that is later than the job date. See JOB.
software modification and maintenance are
of major concern.
active state In microelectronics, the digital (b) Originated in the US Department of
state that causes a given action to occur. It Defense in the late 1970s.
may be either the high state or low state, (c) Facilities. Ada is essentially derived
depending on the circuit and pin in question. from Pascal. This entry will therefore con-
centrate upon those additional features that
are unique to it. Heavy emphasis is placed
aetive wire concentrator In computer net-
upon program readability; it is considered
works, cabinets with star connection to
that it is more important for the program to
individual nodes. In some local area net-
be easily understood than rapidly written. In
works, they are connected in a ring, thus
many applications the cost of maintenance
providing a combined ring/star configur-
can be an order of magnitude greater than
ation. See LOCAL AREA NETWORK, NODE,
that of the original production. The langu-
RING, STAR.
age is therefore rigidly structured and data
typing is strongly enforced; even simple
aetivity In data processing, the percentage operations require a substantial block of
of records in a file that are processed in a code. Machine independence is assisted by
run. See VOLATILITY. the modular nature of Ada, ensuring that
4 ADAPSO
implementation details are confined to a few plete program declares two integers, reads
specialized interface packages. them as input and prints out the largest,
An unusual feature of this language lies in having invoked the package TEXTIO to
its provision for programmable exception perform input/output operations.
handling. Whereas most languages assurne with TEXT 10; use TEXT 10;
the correctness of finished programs, and procedure DEMO is
exceptional conditions are detected and pragma main;
handled by the operating system, Ada P,Q: integer range 0 .. 100;
recognizes that the nature of realtime opera- begin
tion, hardware communication and large GET(P);GET(Q);
sections of code render total reliability NEW UNE;
unattainable, and so allows for the software if P>Q then PUT(P);
detection and correction of errors without else PUT(Q);
recourse to human intervention. In many end if;
control applications, e.g. those involving end DEMO;
heavy machinery, it is vital that the advent of (f) Comments. Ada is a relatively new
a run time fault does not cause the software language whose real worth may not become
to cease to operate. apparent for some years . While it has many
Concurrent programming is supported to advantages in the programming of control
permit the control of parallel processes, computers and other real time activities, with
through the declaration of tasks whose associated ease of software maintenance, it
execution is interleaved. Tasks may co m- is highly verbose and unlikely to compete
municate, usually by means of a rendezvous, with the established block-structured langu-
and nondeterministic operation is permitted. ages for more mundane tasks.
Ada programs may not be necessarily sup- (g) Similar to Pascal, C, PLil. see
ported by an operating system in the host ABSTRACT DATA TYPE, BLOCK STRUCTURE, C,
computer, and they must therefore take COMPILER, CONCURRENT PROGRAMMING, DATA
command of the necessary input/output and ACQUISITION, DATA TYPE, DECLARATION, HIS-
housekeeping operations. Hence a special- TORY OF COMPUTING, HOST COMPUTER, HOUSE-
ized support environment for developing KEEPING, NEST, PARALLEL PROCESSING,
and testing code has been investigated for PASCAL, PLI, REALTIME, RENDEZVOUS, SOFT-
the language. WARE MAINTENANCE, SYNTAX.
In Ada the major units of program struc-
ture are the package and the procedure. ADAPSO US and Canada Association of
Packages may be separately compiled but Data Processing Service Organizations.
where this is done the package must come in
two parts: the specification part, which adaptive channel allocation In communica-
defines the package interface; and the body tions, a method of multiplexing where chan-
or implementation part. The purpose of the nels are allocated according to demand
separation is to permit the compiler to check rather than on a fixed, predetermined plan.
for valid interface usage in the same way as See FREQUENCY DIVISION MULTIPLE ACCESS,
languages such as Pascal do within a single MULTIPLEXING, TIME DIVISION MULTIPLE
compilation unit. The package constructed ACCESS.
thus assists in the correct implementation of
very large programs and provides a frame-
adaptive routing In data communications,
work for the creation of abstract data types.
a routing scheme for packets or messages in
(d) Syntax. Ada is a block-structured
which the behavior adapts to network
language that centers upon the nesting of
changes such as line failures or variation of
statement sequences, successive statements
the traffic pattern. See MESSAGE SWITCHING,
being separated by semicolons. A substan-
PACKET SWITCHING, ROUTING.
tial amount of data and control declarations
are required by the compiler, and, as for
Pascal, the precise rules are described by a adaptive systems Systems that display the
complex set of graphie syntax diagrams. ability to learn to change, alter their state or
(e) Sampie program. The following com- otherwise react to a stimulus.
addressing mode 5
ADC See ANALOG TO DIGITAL CONVERTER. address fleld In programming, the specific
portion of a computer word that contains
ADCCP See ADVANCED DATA COMMUNICA- either the address of the operand or the
TIONS CONTROL PROCEDURE. information necessary to derive that ad-
dress. See OPERAND, WORD.
A/D converter See ANALOG TO DIGITAL CON-
address format In programming, the
VERTER.
arrangement of the parts of a simple
address, such as those required for identify-
ing a channel, module or track on a magnetic
addend In mathematics, the operand of the
disko See ADDRESS, MAGNETIC DISK, TRACK.
addition operation, the number added to the
augend to form a sumo See AUGEND,
addressing (1) In programming, the assign-
OPERAND.
ment of addresses to the instructions of a
program. (2) In communications, the means
whereby the originator or control station
adder In architecture, a device that forms
selects the unit to which it is going to send a
an output resulting from the sum of Mo or
message. See STATION.
more numbers presented as inputs. See FULL
ADDER, HALF ADDER.
addressing mode In programming, the
method of specifying the location of data
during the execution of a machine code
add-in In hardware, an expansion card that
instruction. At the simplest level the
slots into a microcomputer to provide ad-
operand may contain the actual address of
ditional facilities. This is a very simple
the data or, in the immediate mode, the da ta
method of enhancing a microcomputer. The
itself.
boards available allow for additional RAM,
Locating the absolute address in the
additional operating facilities, particularly
operand, however, is uneconomic, inflexible
CP/M, enhanced graphics, modems, instru-
and inefficient for many operations. Un-
mentation etc. See CP/M, EXPANSION CARD,
economic because with al-Mbyte address
MODEM, RAM.
space each operand of each instruction
would need to be 20 bits long. Inflexible
address In programming, (1) a character or because there would be no straightforward
group of characters that identifies a register, method of using the same instruction to
a particular part of storage, or some other access successive locations in successive in-
data source or destination, (2) to refer to a vocations, e.g. in a loop performing a table
device or an item of data by its address. (3) lookup. Inefficient because every data
In communications, the part of the selection operation would involve transfer of data
signals that indicates the destination of a between main memory and the CPU. The
call. (4) In word processing, the location, major dis advantage and restriction to this
identified by an address code, of a specific mode, however, is that the program can
section of the recording medium or storage. only be executed from one position in
memory.
With relative addressing the operand con-
addressability In computer graphics, the tains a quantity that represents a displace-
number of addressable points within a speci- ment from the current value of the instruc-
fied display space or image space. See tion pointer. This is often used in jump
DISPLAY SPACE, PICTURE ELEMENT. instructions and has both the advantage that
the displacement requires fewer bits than the
address bus In buses, a unidirectional bus absolute address and that the instruction will
over wh ich digital information is transmitted function correctly if the program is relo-
to identify either a particular memory loca- cated.
tion or a particular input/output device. Register addressing is employed to en-
Compare CONTROL BUS, DATA BUS. See BUS, hance the power of instruction sets. Register
INPUT/OUTPUT DEVICE, MICROCOMPUTER. addresses may be implicit with the instruc-
6 address modification
.&.ddress rInesrtTaIlOlefyd Address mInestmaloleryd mentation, program relocation and the
accessing of sophisticated data structures.
For example, an address in an 8088/8086
instruction may involve the contents of
1024K 1024K segment register, a base register, an index
(1MB) Booland (1MB ) Bootand register and a displacement. See ABSOLUTE
BASIC ROM BASICRQM
960K 960K ADDRESS, ADDRESS, BIT, BYTE, CPU, DATA
BUS, DATA STRUCTURE, IMMEDIATE ADDRESS,
896K 896K
INDEXED ADDRESS, INDEX REGISTER, INDIRECT
832K 832K
Harddisk ADDRESS, INSTRUCTION COUNTER, LOOKUP
768K 768K ROM TABLE, LOOP, MACHINE CODE INSTRUCTION,
704K SRcA"" ," 704K "R"A""' " TMIEOMNO. RY MANAGEMENT, MEMORY ORGANIZA-
640K 640K
AAMoo AAMon
ordinary ordinary address modification In programming, an
575K memo<y 575K memo<y
mboaay"b'se mboaay"b" e action that causes an address to be alte red in
512K ihnes,ta. lled 5121< ihnes .t.a lled a prescribed way by an arithmetic, syntactic
448K 448K or logic operation. See ADDRESSING MODE.
384K 384K address register In architecture, a special
320K 320K register used by the CPU to store the
address of data to be fetched from, or stored
256K
rAnAolMheoro· 2561< m_RoAdlMheo r·n in, the computer memory. See CPU,
192K 000'" 192K REGISTER.
128K 1281<
address space In architecture, the nu mb er
64K 64K of memory cells that may be accessed by the
CPU. If an 8-bit processor employs a 2-byte
256KPC 2561< XT address then the address space is 65,536
cells, and each cell normally holds 1 byte.
address spaces in an IBM-pe, XT and AT
With 16-bit microprocessors the address bus
normally has 20 lines giving an address space
tion or a particular register may be specified in excess of 1 Mbyte. Bank-switching tech-
with a few bits of the instruction. Data niques can be employed to reduce the
moves from one register to another are fast disadvantages of a sm all address space. See
and efficient because they require no traffic BANK SWITCHING, BYTE, CPU, 8-BIT MICRO-
on the data bus. More importantly, how- PROCESSOR, I6-BIT MICROPROCESSOR.
ever, register addressing provides both high
flexibility in programming and facilitates
memory management. Indexed addressing address track In backing storage, a track
provides a data address by combining the on a magnetic disk containing the addresses
contents of an index register with the fixed of files, records etc. stored on other tracks of
value of an operand; this technique is essen- the same device. See MAGNETIC DISK, TRACK.
tial to update addresses in loop operations.
Indirect addressing implies that the
add time In performance, the time re-
memory location accessed contains not the
quired by a particular CPU to add two
required information but the address of that
multidigit numbers, not including the time
information; this technique provides for
taken to read the numbers or store the
considerable flexibility in programming be-
result. Microcomputers are often rated by
cause the location of the requisite informa-
comparing add times as a criterion of their
tion can be changed during program execu-
relative speed. See MICROCOMPUTER.
tion. 16-bit microcomputers provide for very
sophisticated addressing modes; the Intel
8088/8086 has 25 such modes. A range of ADIS Automatic Data Interchange
registers is employed to facilitate seg- System.