Specifications

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Appendix A Glossary
answer mode A state in which the modem
transmits at the predefined high frequency of the
communications channel and receives at the low
frequency. The transmit/receive frequencies are the
reverse of the calling modem, which is in originate
mode. See also originate mode.
antialiasing Software adjustment to make diag-
onal or curved lines appear smooth and continuous
in computer-generated images. See also aliasing.
antistatic mat A pad that’s set next to a com-
puter upon which components are placed while the
system is being serviced to prevent static damage.
Also can refer to a larger-sized mat below an entire
computer desk and chair to discharge static from a
user before he touches the computer.
antivirus Software that prevents files containing
viruses from running on a computer, or software
that detects, repairs, cleans, or removes virus-
infected files.
APA (all points addressable) A mode in
which all points of a displayable image can be
controlled by the user or a program.
aperture grille A type of shadow mask used in
CRTs. The most common is used in Sony’s Trinitron
monitors, which use vertical phosphor stripes and
vertical slots in the mask, compared to the tradi-
tional shadow mask that uses phosphor dots and
round holes in the mask. See also shadow mask.
API (application programming interface)
A system call (routine) that gives programmers
access to the services provided by the operating sys-
tem. In IBM-compatible systems, the ROM BIOS
and DOS together present an API that a program-
mer can use to control the system hardware.
APM (Advanced Power Management) A
specification sponsored by Intel and Microsoft orig-
inally proposed to extend the life of batteries in
battery-powered computers. It is now used in desk-
top computers as well. APM enables application
programs, the system BIOS, and the hardware to
work together to reduce power consumption. An
APM-compliant BIOS provides built-in power-
management services to the operating system. The
application software communicates power-saving
data via predefined APM interfaces. Replaced in
newer systems by ACPI. See also ACPI.
application End-user-oriented software, such as
a word processor, spreadsheet, database, graphics
editor, game, or web browser.
Application Layer See OSI.
arbitration A method by which multiple
devices attached to a single bus can bid or arbitrate
to get control of that bus.
archive bit The bit in a file’s attribute byte that
sets the archive attribute. Tells whether the file has
been changed since it last was backed up.
archive file A collection of files that has been
stored (often in a compressed format) within a sin-
gle file. Zip and CAB files are the most common
types of archive file formats used with Windows-
based PCs. See also Zip file and CAB file.
archive medium A storage medium (floppy
disk, tape cartridge, or removable cartridge) to hold
files that need not be accessible instantly.
ARCnet (Attached Resource Computer
Network) A baseband, token-passing LAN tech-
nology offering a flexible bus/star topology for con-
necting personal computers. Operating at 2.5Mbps,
it is one of the oldest LAN systems and was popular
in low-cost networks. It was originally developed by
John Murphy of Datapoint Corporation. Although
ARCnet (www.arcnet.com) is no longer used for
office networking, it is still a popular choice for
networking embedded systems, such as heating and
air conditioning systems.
areal density A calculation of the bit density
(bits per inch, or BPI) multiplied by the track den-
sity (tracks per inch, or TPI), which results in a fig-
ure indicating how many bits per square inch are
present on the disk surface.
arithmetic logic unit (ALU) The portion of a
processor where arithmetic and logical operations
are performed.
ARQ (automatic repeat request) A general
term for error-control protocols that feature error
detection and automatic retransmission of defective
blocks of data.
ASCII (American Standard Code for
Information Interchange) A standard 7-bit
code created in 1965 by Robert W. Bemer to
achieve compatibility among various types of data
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