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A20 - Address line 20. The 80286
and higher CPUs allow addresses in real mode to
extend slightly beyond the one megabyte mark,
which causes an incompatibility with some older
programs which expect such addresses to wrap back
to the beginning of the address space. For complete
compatibility with the 8088, newer machines thus
contain circuitry which permits the twenty-first
address line (A20) to be disabled. The CPU then
effectively has only twenty address lines in real
mode, just as the 8088 does, and addresses which
would extend beyond the one megabyte mark wrap
to the beginning of the address space.
ABI - Application Binary Interface. A software
definition that describes the binary instruction
encodings for a particular processor along with
ABR - Available Bit Rate. A class of service
available for ATM. ABR provides a guaranteed minimum
capacity. When additional network capacity is
available , you can burst data above the minimum
rate without risk of cell loss. ABR is intended
for applications where network delays are a concern.
An application using ABR specifies a peak cell
rate (PCR) that it will use and a minimum cell
rate (MCR) that it requires. The network allocates
resources so that all ABR applications receive
at least their MCR capacity. It then shares any
unused capacity in a fair and controlled fashion
among ABR sources. The ABR mechanism uses explicit
feedback to the sources to assure that capacity
is fairly allocated.
An example of an application using ABR is a LAN
interconnection. In this case, the end systems
attached to the ATM network are routers. The ABR
service offers a number of benefits. First, ABR
connections share available network capacity.
They have access to the instantaneous capacity
unused by CBR/VBR connections. Thus, ABR can increase
network use without affecting the quality of service
of CBR/VBR connections. Second, the share of available
capacity used by a single ABR connection is dynamic
and varies between an agreed MCR and PCR. Third,
the network provides feedback to ABR sources so
that ABR flows are limited to available capacity.
The time delays inherent in providing feedback
dictate the use of buffers along a connections
path. Because of the large data rate and a relatively
large propagation delay through a network, these
buffers may be substantial, leading to large delays.
Accordingly, the ABR service is appropriate for
applications that can tolerate adjustments to
their transmission rates and unpredictable cell
delays. Finally, for ABR sources that adapt their
transmission rate to the provided feedback, a
low cell loss ratio is guaranteed.
ABIOS - Advanced BIOS. The IBM XT/286 and
PS/2 models with 80286 or higher processors contain
two separate BIOSes. The ABIOS is a protected-mode
BIOS which is used by OS/2. For machines without
an ABIOS, such as the IBM AT, OS/2 loads the equivalent
of the ABIOS from disk.
ACE - Access Control Encryption.
ACE is the system used in the Security
Dynamics SecurID hardware token system. SecurID
tokens, which are about the size of a credit card
(although much thicker), have been used for secured
access to organizational networks since the 1980s.
ACK - Acknowledgment.
The transmission control protocol (TCP) requires
that the recipient of data packets acknowledge
successful receipt of data. Such acknowledgments
(ACKs) generate additional network traffic, diminishing
the rate at which data passes in favor of reliability.
To reduce the impact on performance, most hosts
send an acknowledgment for every other segment
or when a specified time interval has passed.
ACL - Access Control List. Most network
security systems operate by allowing selective
use of services. An Access Control List is the
usual means by which access to, and denial of,
services is controlled. It is simply a list of
services available, each with a list of the hosts
permitted to use the service.
ACSE - Association Control Service Element.
The method used in OSI for establishing a
call between two applications. Checks the identities
and contexts of the application entries, and could
apply an authentication security check.
ACT - Automated Communications System.
AD - Administrative Domain. A collection
of hosts and routers, and the interconnecting
networks(s), managed by a single administrative
ADC - Analog to Digital Converter. A device
that samples incoming analog voltage waveforms,
rendering them as sequences of binary digital
numbers. Passing waveforms through an ADC introduces
quantization noise. A circuit that generates a
binary (numeric) description of an analog voltage.
ADMD - Administration Management Domain. An
X.400 Message Handling System public service carrier.
Examples are MCImail and ATTmail in the U.S.,
and British Telecom Gold400mail in the U.K. The
ADMD's in all countries worldwide together provide
the X.400 backbone.
ADSL - Asymmetric Digital Subscriber Line.
A variant of DSL, it provides better
download bandwidth and is designed for video on
demand, with almost all the bandwidth reserved
for downstream traffic.
AFP - AppleTalk Filing Protocol. The protocol
in AppleTalk used for remote access to data.
AGP - Accelerated Graphics Port. A
dedicated graphics bus, developed by Intel, slated
for use by the Pentium II (Klamath) processor
that promises to greatly enhance the performance
and quality of 3-D graphics. AGP, supported
by the Intel 440 LX chip set, is designed to improve
the graphical performance of Pentium II systems
by providing a direct link between the PC's graphics
card processor and system RAM through the core
chip set. This gets the graphics card of the slower
(133 MBps) PCI bus and onto its own dedicated
ALAP - AppleTalk Link Access Protocol. Data
link layer protocol Apple uses to allow devices
on the network to transmit and receive frames..
It includes specifications for media access management,
addressing, and data encapsulation/decapsulation,
and frame transmission dialogs.
ALU - Arithmetic Logic Unit - A circuit
that performs math calculations and/or logical
ANSI - American National Standards Institute.
The U.S. standardization body. ANSI is a member
of the International Organization for Standardization
APA - All Points Addressable. A mode in
which all points of a displayable image can be
controlled by the user or a program.
API - Application Program Interface. A
system call (routine) that gives programmers access
to the services provided by the operating system.
In IBM compatible systems, the ROM BIOS and DOS
together present an API that a programmer can
use to control the system hardware.
The defined set of calls which a program may make
to interact with or request services of the operating
system or environment under which it is running.
Because the inputs and outputs of the calls are
well-defined, a program using the API can continue
using the identical calls even if the internal
organization of the program providing the API
APIC - Advanced Programmable Interrupt Controller.
A function supplied the Intel Pentium processor.
APL - A Programming Language. An interactive,
mathematically oriented language which is well-suited
to manipulating matrices. Originally using greek
letters and numerous special symbols, thus requiring
a special display, versions are now available
which use keywords in place of the special symbols.
APM - Advanced Power Management. A specification
sponsored by Intel and Microsoft originally proposed
to extend the life of batteries in battery powered
computers. APM allows 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
APPC - Advanced Program to Program Communications.
A component of IBM's System Network Architecture.
APPC is designed to allow communications between
programs running on different systems on a more
or less peer-to-peer basis.
ARC - Advanced RISC Computing. ARC names
area generic method of identifying devices within
the ARC environment.
ARCnet - Attached Resource Computer Network.
Developed by Datapoint Corporation and has
been a popular reliable LAN for years. Because
of its popularity, standards existed for ARCnet
even before IEEE Project 802 was established.
The IEEE 802.4 specification, which defines token
passing on a bus using broadband technology, is
the standard most similar to ARCnet. However,
because ARCnet is a baseband network, it is very
inexpensive and easy to install. ARCnet can have
a star or bus topology. Often, however, it is
considered to have a distributed star or tree
topology. Manufacturers consistently follow ARCnet
standards, and the products released for ARCnet
networks are usually compatible with equipment
from other vendors. Because it uses both passive
and active hubs, ARCnet is excellent for elaborate
ARLL - Advanced Run Length Limited. More
complex yet powerful derivatives of the RLL
(Run Length Limited) scheme. Include 1,7 and
3,9 encoding. Allows 34 or more sectors per track.
ARP - Address Resolution Protocol. The
Internet protocol used to dynamically map Internet
addresses to physical (hardware) addresses on
local area networks. Limited to networks that
support hardware broadcast. Used to dynamically
discover the low level physical network hardware
address that corresponds to the high level IP
address for a given host. ARP is limited to physical
network systems that support broadcast packets
that can be heard by all hosts on the network.
ARPA - Advanced Research Project Agency. An
agency of the U.S. Department of Defense responsibility
for the development of new technology for use
by the military. ARPA, formerly known as DARPA,
was responsible for funding much of the development
of the Internet we know today, including the Berkeley
version of UNIX and TCP/IP.
ARPANET - A packet switched network developed
in the early 1970's. The grandfather of today's
Internet. ARPANET was decommissioned in June 1970.
AS - Autonomous System. A collection of
routers under a single administrative authority
using a common Interior Gateway Protocol for routing
ASCII - American Standard Code for Information
Interchange. A standard seven bit code created
in 1965 by Robert W. Bemer to achieve compatibility
among various types of data processing equipment.
The standard ASCII character set consists of 128
decimal numbers, ranging from 0 through 127, assigned
to letters, numbers, punctuation marks, and the
most common special characters. In 1981 IBM introduced
the extended ASCII character set with the IBM
PC, extending the code to eight bits and adding
characters from 128 through 155 to represent additional
special mathematical, graphics, and foreign characters.
ASIC - Application Specific Integrated Circuit.
A chip designed for a particular customer
or system, typically from standard cells and/or
gate arrays. May ultimately be sold as a standard
ASN.1 - Abstract Syntax Notation One. The
OSI language for describing abstract syntax.
ASVD - Analog Simultaneous Voice/Data.
A modem technology that comes with video phone
capabilities and is compatible with the v.80 standard
that supports ITU's H.324 parameter standard allowing
for video, voice, and to be shared simultaneously
over high speed modem connections.
AT - Advanced Technology. A computer model
introduced by IBM in 1984 where the CPU, memory,
and I/O bus all shared a common 8 MHz clock. Known
today as the ISA bus. Replaced the IBM XT with
a speed nearly five times as fast. Contained the
80286 CPU and had 16 bit card slots.
ATA - Advanced Technology Attachment. Same
as IDE (Integrated Disk Electronics). A disk drive
implementation designed to integrate the controller
onto the drive itself, thereby reducing interface
costs, and making firmware implementations easier.
Introduced in March 1989, it defines a compatible
register set and a 40 pin connector and its associated
ATA-2 - Advanced Technology Attachment-2. A
compatible extension of ATA (IDE) The most important
additions are performance enhancing features such
as fast PIO and DMA modes. Another important novelty
is the souped up Identify Drive command allowing
a drive to tell the software exactly what its
characteristics are. This is essential for both
Plug and Play and compatibility with future revisions
of the standard. Also called Fast ATA, Fast
ATA-2, and Enhanced IDE (EIDE).
ATAPI - Advanced Technology Attachment
Packet Interface. A standard designed for
devices such as CD ROMS and tape drives that plug
into an ordinary ATA (IDE) port. The principal
advantage of ATAPI hardware is that it is cheap
and works on every PC with an IDE adapter. For
CD ROMS, it has somewhat lower CPU usage compared
to proprietary adapters but there is no performance
gain otherwise. For tape drives, ATAPI has potential
for superior performance and reliability compared
to the popular QIC117 floppy tape drives.
ATM - Asynchronous Transfer Mode. A versatile
broadband network architecture capable of delivering
in varying speeds. The original specification
for ATM came from the International Telecommunications
Union (ITU) , the organization whose standards
address the worldwide telecommunications infrastructure.
In the early 1980's the ITU defined Integrated
Services Digital Network (ISDN), which is
now called N-ISDN for narrowband ISDN. N-ISDN
had two access interfaces, or transfer rates (Basic
144 kbps and Primary 1.544 Mbps). In the late
1980's, the ITU further enhanced N-ISDN by bringing
out the specifications for B-ISDN, or broadband
ISDN. Unlike N-ISDN, B-ISDN offered much higher
transmission rates, up to 622 Mbps. The signals
generated by B-ISDN are carried by ATM. ATM transmits
in what is known as a cell stream. A cell is a
term for ATM broadband transmission that can be
thought of as a predefined data packet. The data
packet, or cell, is 48 bytes long with a 5 byte
header for addressing.
Asynchronous Transfer Mode (ATM) is a cell-based
fast-packet communication technique that supports
data-transfer rates ranging from sub-Tl speeds
(less than 1.544 Mbps) up to 1 0 Gbps. Like other
packet-switching services (Frame Relay, SMDS),
ATM achieves its high speeds in part by transmitting
data in fixed-size cells, and dispensing with
error-correction protocols. Instead, it relies
on the inherent integrity of digital lines to
ensure data integrity. ATM networks are extremely
versatile. An ATM network can be treated as a
single network, whether it connects points in
a building or across the country. Its fixed-length
cell-relay operation, the signaling technology
of the future, offers more predictable performance
than variable-length frames. And it can be integrated
into an existing network as needed, without having
to upgrade the entire LAN.
ATP - AppleTalk Transaction Protocol. A
transport layer protocol that provides reliable
guaranteed delivery of packets from a source socket
to a destination socket.
ATPS - AppleTalk Print Services. The software
utility within the AppleTalk Networking Operating
System that contains Macintosh computer printer
on an Apple Network.
AUI - Attached Unit Interface Cable. A
four twisted pair interface cable that connects
an Ethernet device to an Ethernet external transceiver.
AUP - Acceptable Use Policy. Many transit
networks have policies which restrict the use
to which the network may be put. For example,
some networks may only be used for non-commercial
purposes. Some AUP's limit the type of material
which can be made available to the public. Enforcement
of AUP's varies with the network.
AVI - Audio Video Interleave. A storage
technique developed by Microsoft for their Video
for Windows product that combines audio
and video into a single frame or track, saving
valuable disk space and keeping audio in synchronization
with the corresponding video.
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Compiled by Scott
McArdle, MagnaCom Limited. I hope this list
has helped you and if there is an item that should
be on this list, please let me know. Thanks. PS,
I've spent 100's of hours maintaining this list,
please don't be a LAMER.