Common Terms
Here are some common computing, connector, cable and
wiring terms.
ACPI - "Advanced Configuration and Power
Interface" - The latest generation of DOS-based power
management software for PCs. ACPI replaces the older Intel APM
(Advanced Power Management) software utility. ACPI does more
than just manage time outs during periods of inactivity, it
dynamically monitors power usage within the computer's systems and
assigns power accordingly. ACPI controls are found in your PCs'
BIOS.
Active matrix display - A type of
flat-panel display found on most of today's laptop computers. Active
matrix technology differs from "passive matrix" only in that
the screen is refreshed more frequently, creating much better picture
quality with better viewing angles. The most common type of active
matrix screen is called TFT (or "thin film transfer"). The
two terms are often used synonymously.
Adapter Card - An electronics board installed in a PC,
which provides a network interface to and from that computer. A
network interface card (NIC) is a type of adapter card.
ADSL - Asymmetric Digital Subscriber Line - A term for one-way
high speed transmission of signals over plain single twisted-pair
wiring already run to residences. ADSL is provisioned with
greater downstream than upstream rates (hence asymmetric). These rates
are dependent on the distance of the user to the Central Office and
can vary from as high as 6 Mbps to as low as 128 Kbps.
AGP - "Accelerated Graphics Port" - A relatively new
type of dedicated PC graphics bus designed by Intel Corp to more
efficiently render 3D graphics. The AGP can transfer data at a rate up
to 528MB/sec. By comparison, the more common PCI (Peripheral
Component Interconnect) bus, used in Pentium and Mac machines, has a
maximum transfer rate of 132MB/sec. AGP's big bandwidth allows
games and 3D apps to use more realistically-rendered textures and
faster frame rates and to store this data in system, instead of video,
memory. This reduces the performance hit to the system as
graphics are presented.
Alpha Channel - In computer graphics, a portion of
each pixel's data that is reserved for transparency information.
32-bit graphics systems contain four channels -- three 8-bit channels
for red, green, and blue (RGB) and one 8-bit alpha channel. The
alpha channel is really a mask -- it specifies how the pixel's colors
should be merged with another pixel when the two are overlaid, one on
top of the other.
AMR - "Audio Modem Riser" - An Intel
specification for analog I/O (Input/Output) functions on motherboards.
An AMR card removes analog I/O functions from the motherboard,
relegating them to a plug-in "riser card" (a.k.a. a
"daughter board"). By doing this, motherboard
manufacturing is not restrained by the FCC and International Telecom
certification processes which can often get bogged down in red tape.
AMPS - "Advanced Mobile Phone Service" -
The analog celluar phone standard first introduced by AT&T in
1983. AMPS phones operate in the 800 to 900 Megahertz (MHz)
radio spectrum. The term is "cell" phone because the
signals are sent from radio transmitters that cover a broadcast area
known as a cell.
API - "Application Program Interface" -
A series of software routines and development tools that comprise an
interface between a computer application and lower-level services and
functions (e.g. the operating system, device drivers, and other
low-level software). APIs serve as building blocks for
programmers putting together software applications. Sometimes called
"Application Programming Interface."
ASP - "Application Service Provider" -
A growing number of "apps-on-tap" websites where
applications are available for rent. ASPs allow small businesses
to have access to programs and services that they might not otherwise
be able to afford on their local area network.
ASP - "Active Server Pages" - A
sophisticated server-side application-building environment that is
used to dynamically create HTML-like pages (viewed on a normal browser
as a HTML page). An ASP page is an TML page containing, client-side
script and HTML tags, and a script than runs on the server, referred
to as 'server-side scripting' (using a scripting language like
Javascript or VBScript). ASP supports integration with other Microsoft
server products, such as Microsoft Transaction Server, and access to
COM objects.
ATA - "Advanced Technology Attachment" - The
common disk drive interface technology that puts the drive controller
right on the drive itself. There are a number of ATA versions,
from the original a.k.a. IDE) to the 33MBps ATA-33 (a.k.a. Ultra-ATA)
to the newest standard, ATA-66 which operates at 66MBps.
Athlon - The name of AMD's new chip intended to
compete with Intel's Pentium III. The Athlon was formerly referred to
as the K7. The September '99 issue of PC World claims that the
600MHz Athlon is on average 9% faster than a 600MHz PIII.
In graphics tests, the Athlon was 21% faster running 3D modeling
software. For comparisons and benchmarks, see AMD's Athlon
page.
AWG - "American Wire Gauge", for rating the
'size' of a wire, the smaller the number, the larger the size.
Backplane - A printed circuit board in an
electronics device with sockets into which other circuit boards can be
plugged. In most PCs, the backplane is the large board that
contains the ISA, PCI and other sockets for modem, video, sound and
other expansion cards. Sometimes used synonymously with
"motherboard".
Bandwidth - The amount of information or data that can
be sent over the Internet during a given period of time. Bandwidth is
usually stated in bits per second (bps), kilobits per second (Kbps) or
megabits per second (Mbps).
BIOS - "Basic Input/Output System" - The BIOS is
the root software in a PC that contains all of the basic code for
controlling drives, keyboard, monitor, mouse, serial ports, etc. The
BIOS acts as a bridge between the hardware and the operating system.
The BIOS resides on a ROM chip (rather than in RAM), so that a
computer can be booted.
Bluetooth - An open standard for short-range wireless
communications being developed by a cooperative of mobile phone,
computer and PDA manufacturers. The standard allows all of your
(Bluetooth-compliant) personal tech devices to communicate with each
other. For more info, see the Bluetooth
website.
BNC - A twist-lock connector used in coaxial cable
networks.
Bridge - A data communications device that connects
two or more networks and forwards packets between them and function as
routers. Bridges read and filter packets and frames. Bridges do not
require IP addresses and will pass broadcast traffic.
Broadband - A transmission medium or channel that has a wider
bandwidth than one voice channel (with a carrier wave of a certain
modulated frequency). It allows multiple services like voice, data,
video, etc. to transit over the network.
Browser-safe colors - The 216 colors in the common 256-color display
palette that are rendered the exact same way on both Mac and PC
operating systems. You should use these colors if you want your
Web graphics and colored elements to look consistent on both
platforms.
Bus - A portion of computer architecture which carries
data from one component to another. As a general rule,
more than one component is attached to a bus, and the particular
component (or section of memory) being used is selected through the
use of address lines in the bus.
Cache - (pronounced "cash") - A form
of high-speed storage that can be either a section of main memory (as
in "memory caching") or an independent storage device
("disk caching"). Memory caching is effective because
most programs access the same data or instructions over and over
again. By storing this information in cache memory, overall data
processing speed is improved. Level 2 (L2) cache, which is
common in many of today's computers, is usually located on a second
chip between the main computer processor and the DRAM.
CDPD - "Cellular Digital Packet Data" -
A wireless radio frequency (RF) communication service that can deliver
data packets over existing cellular phone networks that have been
upgrading for CDPD. CDPD is capable of transfer speeds of up to
19.2 kbps. The CDPD packets are actually sent between pauses in
the cellular phone conversations. CDPD cellular modem service is
currently available in about 65 US cities.
Circuit-Switched Cellular - A system for transferring
modem data over a conventional analog cellular network that has not
been updated for CDPD communication.
CLEC - "Competitive Local Exchange
Carrier" - A telecom company that is in competition with
the local Bell (or other) telephone company. The term was coined
after the 1996 Telecommunications Act which deregulated the telecom
industry. CLECS include cable companies, ISPs, cellular providers and
others.
CMS - Cable Management System, refers to the products used to
neaten-up a cable plant.
CO - Central Office - A circuit switch that terminates
all the local access lines in a particular geographic serving area; a
physical building where the local telephone company’s switching
equipment is found. DSL lines running from a subscriber’s home
connect at their serving Central Office.
Coaxial cable - A cable with one inner conductor, and an outer shield
(which is usually grounded), insulated from one another by a
dielectric foam. Both conductors share the same axis, thus
the name coaxial. Coaxial cable is used in 10-Base2 Ethernet,
and in a variety of RF applications, including CATV. Each
type of coaxial has a characteristic impedance (expressed in Ohms).
Coax cable is rate with an RG prefix (old military jargon for
"Radio Guide" and followed by the cable type (expressed in a
number) and the suffix "/U" if it's a general utility cable
(as opposed to special application coax made of different material,
designed for shorter runs, etc.). RG-6/U coax is a 75-ohm cable
designed for internal wiring of cable and antenna television. RG-59/U
coax is a 75-ohm cable commonly used in video transmission, and CB,
Ham radio and TV antennas.
CompactFlash - A type of flash memory card,
approximately one-third the size of a PC card. CompactFlash
cards can be used in Type I & II PC-Card slots with an adapter.
One factor that distinguishes CompactFlash cards from other types of
flash memory cards is that they have their own controller onboard so
that cameras, PDAs and other devices that use the cards are not
burdened with the controller software. CompactFlash cards comes in
sizes from 2MB to 64MB.
Connecting Block - A plastic block containing
metal clips for connecting wire runs in a distribution closet.
Concentrator - A high-density hub, usually designed to
allow for future expansion.
CPE - Customer Premise Equipment -
Communications equipment that resides on the customer’s premises.
The CPE for DSL services is often called a DSL "modem".
Cross-over Cable (Usually referring to Ethernet) - A
cable that crosses the transmit and receive pins appropriately so that
two devices can communicate directly without the use of a hub, or
similar intermediate device.
CSMA/CD - Carrier Sense Multiple Access / Collision
Detect. A transmission technique that operates as follows:
Before a device sends a packet it checks to see if another device is
already transmitting. If the line is clear it will send its packet. If
two devices start sending at the same time a 'collision' is caused,
the devices can detect this collision, and will each wait a random
amount of time before re-retrying. This is the access method used by
Ethernet.
dB, decibel - dB is an abbreviation for
"decibel". One decibel is one tenth of a Bel, named for
Alexander Graham Bell. The measurement quoted in dB describes
the ratio (10 log power difference, 20 log voltage difference, etc.)
between the quantity of two levels, the level being measured and a
reference. This
page is a more detailed reference.
DEMARC - Demarcation point, identifies the division of
a loop or circuit responsibility, where the telco's responsibility
ends, and the subscribers begins.
Dedicated Line - A transmission circuit that is
reserved by the provider for the full-time use of the subscriber.
DIP switches - "Dual Inline Package" switches - Small
switches found on motherboards and other computer devices. By
turning the switches on or off, the user can select different
operating options.
Downstream/Upstream - Downstream refers to data
flowing from the source such as an Internet service provider (ISP) to
the end user. Upstream refers to data flowing from the end user back
to the ISP.
DRDRAM - "Direct RAMbus Dynamic Random Access Memory" -
A recent generation of RAM technology. DRDRAM draws less
power (almost a third less than SDRAM), has clock speeds of up to a
dizzying 800MHz, allows for multiple channels of memory for up to four
parallel banks of RAM, and a data path that's twice as wide as
existing SDRAM (two bytes instead of one).
DSP - "Digital Signal Processor" - A
microprocessor that specializes in calculations related to translating
analog signals into digital ones. DSPs are used in audio and
video compression, voice processing, modems, hearing aids, seismic
sensors, anyplace where rapid analog to digital conversion and signal
clarification is required.
DVD - "Digital Video (or Verastile) Disc" -
An improved CD-ROM-like technology that can fit between 4.7GB to 17GB
of multimedia data on a single disc. DVD is "backwards
compatible" with CD-ROMs, and most DVD drives and players will
play audio CDs and CD-ROMS. Drives for the latest version of
DVD, called DVD-2 (or DVDII), can also read CD-R (Recordable) and
CD-RW (Re-Writable) discs.
EIDE - "Enhanced Integrated Device
Electronics" - Refers to a type of ATA disk drive interface
standard where the controller for the device is part of the device
itself, eliminating the need for a separate adapter card. EIDE
adds features onto the older IDE standard, such as larger capacity (up
to 8.4GB), faster access times, and burst transfer (large chunks of
data at once).
Ethernet - A popular type of local area network (LAN)
developed by Xerox in 1976 and common in many of today's office
networks. Two popular Ethernet configurations are 10Base-T (carrying
10 megabits per second) and 100Base-T (at 100Mbps). Ethernet
networks are often connected by twisted-pair cabling, but can also be
connected by coaxial and fiber-optic cables.
F-connector - Connector type used in coax for cable TV
connections. Can be threaded or push-on type.
Firewall - A set of related programs, located at a
network gateway server, that protects the resources of a private
network from users from other networks. (The term also implies the
security policy that is used with the programs.) An enterprise with an
intranet that allows its workers access to the wider Internet installs
a firewall to prevent outsiders from accessing its own private data
resources and for controlling what outside resources its own users can
access.
FOIRL - Fiber Optic Inter-Repeater Link
Full-Duplex - A physical medium in which data can
travel in both directions at the same time, using 100% of available
bandwidth in the communication channel.
Half-Duplex - A physical medium in which data travels
in one direction, or the other at any given time, using 50% of the
theoretical bandwidth of the communication channel.
Hub - Usually referring to Ethernet - A wiring
connection device which accepts cables from PCs, servers, etc.
The hub retransmits signals received from one device to all other
devices connected to the hub. If more ports are needed than are
present on a single hum hub, multiple hubs can be cascaded together,
through the use of a cross-over cable (see below), a special port
designated on the hub, usually as 'MDI', or with a 'cascading' cable
and port.
Horizontal Cable - The portion of a cable system that
extends from the wall jack to the device (phone or PC typically).
Also refers to the cable used to connect a hub or PBX to a patch
panel.
HVAC - Heating, Ventilating, and Air
Conditioning systems.
IDC - Insulation Displacement Connector. A
connector type found in most network termination equipment, which
works by removing the insulation on a wire as the connection is made,
usually by either piercing the insulation, as is the case with RJ
jacks, or by using a special tool to force the individual wire between
two closely placed 'blades' of a connector, where the insulation is
removed as the wire is forced between the blades. This type of
connector speeds termination of wire, and allows for a simple,
reliable connection.
ISDN - Integrated Services Digital Network - A digital
network provided by the telephone company. ISDN lines typically
contain two 'B' channels, and one 'D' channel:
B Channel = Bearer Channel, 64kbps. In the US, this is the
channel that carries the user data.
D Channel = Data Channel, 16kbs. This is the channel that
carries signaling information, used by the ISDN network to connect or
disconnect 'B' channels.
Kbps - Kilobits per second - A measure of
bandwidth capacity or transmission speed. The acronym stands for a
thousand bits per second.
MAC Address - Media Access Control Address - A unique 32-bit
number (usually expressed in hex) assigned to a device to identify it
on the network. MAC addresses are 6 bytes long, the first three
bytes are unique to each manufacturer, the last three are a sequential
number. Every network device in the world should have a unique
MAC address.
Monster-Cable - Refers to pricing strategy for
otherwise normal cable.
Mbps - Million bits per second - A measure of
bandwidth capacity or transmission speed.
Multi-Mode (MM) - Refers to fiber-optic cable. Common size is
62.5/125. This means the core (or actual fiber) is 62.5 microns, the
cladding is 125 microns. Multi-Mode fiber is used in most typical LAN
applications, and is limited to a distance of 2Km. As its name implies
multl-mode can carry multiple 'conversations' based on different light
input attenuations.
MUX - MUltipleXer . A device which combines multiple
low-bandwidth channels into one channel to be carried over a single
high-bandwidth carrier. At the opposite end of the circuit another
MUX/DEMUX converts the high-bandwidth signal back into its multiple
low-bandwidth channels.
NAT - Network Address Translation - Provides a
pseudo-dynamic connection with the internet in a private IP space, by
allowing a LAN to operate using "private" unroutable
addresses, and exposing a small number of routable addresses on the
external interface of a firewall.
NIC - Network Interface Card - The circuit board or other form of
computer hardware that serves as the interface between a computer and
the communications network. Types of NICs include Ethernet,
Arcnet, token ring, etc.
Node - A device on a network, other than a hub. Ie:
PC, router, bridge, sniffer, printer.
Patch Cable - A short length of network cable used to
connect two devices together.
Patch Panel - A device where data cables are
terminated. Patch panels allow wiring to be easily re-configured based
on need. Patch panels are more for convenience and are not needed in
order to make a successful data network.
PC-100 main memory bus - A bus technology introduced
in the middle of 1998, which replaced the older 66MHz bus. PC-100
buses are approx. 20% faster than the older bus. To match the faster
bus speed,100MHz SDRAM ("Synchronous Dynamic Random Access
Memory") modules are required on all PCs with the PC-100 bus.
Both Apple and PC makers (circa early '99) are using the PC-100
bus/100MHz SDRAM combo. See also bus and SDRAM.
PCI - "Peripheral Component Interface or
Interconnect" - A 64-bit local bus that was introduced to
meet the more demanding needs of Pentium processors. The maximum
transfer rate on a PCI bus is 132 MB/sec.
PCMCIA card - "Personal Computer Memory Card
International Association" card - (Also called a "PC
Card") - A credit-card size removable card that fits into a
compatible slot on many digital devices (laptops, Personal Digital
Assistants, wireless communications devices). PC cards house
such things as additional memory, modems and network interfaces, and
come in a variety of form-factors, the most common of which are
"Type II" and "Type III".
PCS - "Personal Communication Services" -
The FCC's (and wireless industry's) term for digital cellular
technologies. PCS standards include GSM ("Global System for
Mobile Communications"), CDMA ("Code-Division Multiple
Access") and TDMA ("Time Division Multiple Access").
PCS phones are completely digital and operate in the 1900 MHz
frequency range.
PDF - "Portable Document Format" - A
document format developed by Adobe to allow documents to be read
"cross-platform," without the viewer needing the program in
which the document was created. The Adobe Acrobat Reader
(available at Adobe's website) is
needed to view or print a document saved in PDF format, .
Plenum - An air-return area in a HVAC system.
Plenum is NOT a type of cable coating, but rather a rating of
cable for use in a 'plenum' area. Some plenum grade cable is
PVC-jacketed.
POSIX - "Portable Operating System Interface for
uniX" - A set of standards that define the interface between
computer applications and POSIX-compliant operating systems.
POSIX-compliant Unix systems allow developers to more easily port
programs to run on the many flavors of Unix, Linux and even Windows
NT.
POTS - Plain Old Telephone Service - Term
referring to the class of service provided in a regular residential
(analog) phone line.
PVC - A common cable-jacket material.
Raised Floor - A type of flooring often found in
computer rooms. Floor panels are set on risers usually
10"-12" above the actual floor, used to route cables under
equipment, and provide a plenum for air conditioning.
RCA connector - A round, press-on connector commonly
used for consumer-grade audio and composite video connections.
In most recent home stereo equipment, the jacks are color-coded as
follows: red (audio-Right), black or white (audio-Left) and
yellow (composite video).
RISC - "Reduced Instruction Set Computer" -
A microprocessor design that evolved from the earlier CISC
("Complex Instruction Set Computer") designs. The RISC
chip, developed at IBM in the early '70s, needed fewer operating
instructions (hence the name), was faster than CISC processors (at
least when executing simple instructions), and was even cheaper to
manufacture. The Motorola PowerPC chips, used in recent Macs,
are RISC designs. Other RISC chips include DEC's Alpha and Sun's
SPARC.
RJ-11 - The most common type of telephone jack in the
world, a 6-pin male modular jack (or plug) that connects to a
female jack on a wall (or an RJ-11 adapter). RJ-11 jacks are
usually only wired for four pins and only two of them (usually the red
and the green wires) are used for the phone signal. The second
pair can be used to carry a second phone line or to run low-wattage
electronics, such as lights on phones. The second twisted pair
of wires are increasingly being used for phone-based home networks (to
connect your home PCs through your phone wiring). "RJ"
stands for Registered Jack. The numbers that follow RJ (RJ-45,
RJ-61X, etc.) are designations assigned by the FCC
RJ-45 - Refers to a type of jack, similar to an RJ-11
(phone) jack, only wider, with 8 conductors, rather than 6.
RJ-45 connectors are used for a variety of
purposes including networking and telephony.
Riser - A vertical shaft or conduit used to route
cables between floors.
Router - The device that connects multiple computer
networks by reading the address information on all data packets. The
packet information is read, and the packets are then forwarded to the
appropriate end station. Routers provide more functionality than
bridges, which simply connect dissimilar networks. Routers may
be used to connect LANs to LANs or LANs to WANs.
RS-232 - An industry standard for the serial interface that your
computer uses to communicate with modems and other serial peripheral
devices. Serial refers to the fact that the data is transferred one
bit at a time. In a parallel connection (such as a parallel
printer), data is sent in groups of bits over multiple wires.
RS-232 is being gradually replaced in the PC marketplace by USB.
RTFM - Programmer slang for for "Read The
Freaking Manual!" .... or words to that effect.
SC - A type of fiber connector. Terminates one pair of
fiber into one jack. Looks like two squares side-by-side.
SCSI - "Small Computer System Interface" -
A high-speed parallel interface standard used to connect a computer's
CPU to a peripheral device such as a printer, hard drive, or another
computer.
SDMI - "Secure Digital Music Initiative -
The record industry's attempt to stop MP3 piracy. When the scheme is
implemented (originally planned for deployment by Q4 1999), all new
commercial CDs will include a digital watermark. Playback on
SDMI-compliant MP3 players (and other Internet music devices) will
only be possible if the commercial releases contain the digital
watermark. Copies of songs that have been pirated will not have
the watermark and will therefore not work. For more info see www.sdmi.org.
SDRAM - "Synchronous Dynamic Random Access
Memory" - A form of DRAM that operates at higher clock speed than
traditional DRAM, due to a "bursting" technology in the DRAM
that predicts the location of the memory address most likely to be
accessed next.
SDSL - "Symmetric Digital Subscriber Line" -
Also called single line service, SDSL provides the same amount of
bandwidth in both directions.
Shell - A term for that operating system's user interface (most
commonly used to describe the user interface of Unix, but also used to
describe the user interface of other operating systems as well.)
In short, it's called a shell because it's the outer-most layer of the
OS. The inner-most layer, the heart of the OS's code is called
the kernel. "Shell out" is a Unix term for moving from
a program within Unix to the shell interface.
SM - "Single-Mode" - Refers to a type of
fiber-optic cable. Common core is 5-10 microns. SM fiber has a much
longer working distance, but because of it's small core size requires
the use of a more precise transmitter light source, ie: laser. SM is
used in most WAN applications, such as Telco distribution. Because of
it's small core size, single-mode fiber can carry only one
conversation.
SIMM - "Single Inline Memory Module" -
A plug-in circuit board that holds surface-mounted RAM memory chips.
The "single inline" part of the name refers to the fact that
the pins on the module that plug into the SIMM socket on the
motherboard form a single row on the bottom of the circuit board.
A newer, higher bandwidth type of memory module called a DIMM
("Dual Inline Memory Module") is common on most newer
systems.
Simplex - A transmission medium in which data travels
in one direction only.
Skins - The user-created graphical interfaces for MP3
players, games like Quake and other types of software that allow the
creation of such custom interfaces.
SmartMedia card - (less commonly known as an SSFDC or
"Solid State Floppy Disk Card") - A form of removable Flash
RAM Memory card used in digital cameras and other handheld computer
devices, such as the Diamond Rio MP3 player. SmartMedia cards
come in both 3.3 and 5 volt versions with storage capacity from 2MB to
16MB (and larger).
Socket 7 - The socket on PC motherboards that the
original Intel Pentium class processors plug into. For Pentium II and
III, Intel packaged its processor in a plastic cartridge that fits
into a slot (Slot 1 or Slot 2) on the motherboard. However, chip
makers like AMD and Cyrix continue to use the socket.
SOHO - "Small Office/Home Office" - As
more people telecommute and start home businesses, the SOHO has become
a desirable target market for office supply and computer companies.
S/PDIF - "Sony/Philips Digital InterFace" -
A consumer-grade digital stereo transmission format, now common on
much recording studio equipment and PC sound cards.
Spread spectrum - Any of several RF modulation
techniques that use a significantly wider band to transmit a signal
than the original (baseband) signal. The advantages of
spread-spectrum modulation is its high immunity to noise. Two
spread spectrum techniques are direct-spreading and frequency-hopping.
In frequency-hopping systems, the bandwidth used by any given
transmitter at any moment in time is roughly equivalent to the
bandwidth of the baseband signal, but both the transmitter and the
receiver change frequencies (within a fairly wide band) in a
pre-determined sequence.
SRAM - "Static Random Access Memory" -
A form of RAM that retains its memory only as long as there is power
to run the device, without being refreshed. (DRAM needs to be
periodically refreshed.)
ST - Type of fiber connector. Terminates each
fiber individually. Looks similar to a mini BNC connector.
Stackable - A term referring to Ethernet hubs that can
be connected together, usually only with similar brands/models, so
that the number of ports is increased, without adding additional hops.
Store-and-forward - A type of communication system in
which messages are received at an intermediate routing point in a
network, recorded (i.e. stored), and then transmitted (i.e. forwarded)
to another routing point, or their final destination, at a later time.
This allows messages to be sent to machines that may be offline or
transferred over a net at off-peak hours when rates and/or traffic are
lower. Most e-mail traffic is handled in store-and-forward
systems.
S-video - "Super Video" - A type of
video technology that delivers a much sharper image to TV monitors
than composite video (in which the Red Green Blue, and often even the
audio, are mixed together). S-video carries color (chrominance)
and brightness (luminance) separately. Video cameras with
S-Video usually have both an S-Video output jack and the more common
RCA-type audio/video connections (used in composite video). You
can only take advantage of S-Video playback if your TV has S-Video
input.
Switch - A device which allows for a large network to
maintain an effective data throughput by segmenting it into multiple
parts, then passing traffic only to the segment that contains the
destination host, thus reducing traffic on the other segments.
T-1 - "Digital Transmission Rate 1" -
A leased line phone connection capable of carrying 1.544 megabits of
data per second. T-1 lines are commonly used to connect
networks, ISPs, web providers and others to the Internet.
TDMA - "Time Division Multiple Access"- In
wireless technology, a digital wireless service that uses a
bandwidth-sharing technique referred to as "time-division
multiplexing" (TDM). TDM divides a radio frequency into
time slots and then allocates slots to multiple mobile callers.
With TDMA, a single radio frequency can support multiple, simultaneous
data transmissions. TDMA is used by the GSM digital cellular
standard, which is popular in Europe and almost non-existant in the
US.
TDR - Time Domain Reflectometer - A device used to
measure cable length based on reflection time of a generated signal.
Token Ring Network - A local area network
configuration that forms a closed ring of machines where network
traffic is managed through the passing of digital tokens. A
machine on the network cannot send data unless it "has the
floor" via the token. A token ring can operate at up to 4
megabits (4 million bits) per second.
Tone Generator and Inductive Amplifier - The
tone is connected to one end of a cable, and places a (typical) 2 kHz
audio tone on the cable. The inductive amplifier can detect this
signal without having to cut or damage the cable being tested. The
inductive amplifier usually has a range of about 1"-4" from
the cable. Typically used to identify or trace cables.
TWAIN - "Technology (or Toolkit) Without An
Interesting Name" - An interface standard for scanner, fax,
graphics and text-reading (OCR) software. It allows images to be
scanned directly into the image editing software. Most recent
scanners come with TWAIN drivers, and most recent image-editing
software accept data from TWAIN.
Twin-Ax - Twinaxial cable - Similar to coax, but
with two internal conductors, surrounded by a common shield.
UART - "Universal Asynchronous
Receiver/Transmitter" - A chip that performs the conversion from
serial data (transmitted and received by a serial port) to parallel
form, which is used internally by a computer. The UART is
a common source of bottlenecks in a computer/modem relationship.
Newer computers use the 16550 UART chip which has a 16-bit buffer.
This has helped keep pace with today's faster modems.
Ultra ATA - (a.k.a. ATA-4, Ultra DMA, ATA-33,
DMA-33) The latest specification for the ATA/EIDE disk
controller standard. EIDE, or "Enhance Integrated
Electronics Interface" is a technology that puts all of the
controller electronics for disk drives onto the drives themselves.
Ultra ATA allows for much faster data transfers that are twice as fast
as the previous ATA-2 (up to 33.3 megabits per second).
"ATA" stands for "Advanced Technology Attachment"
and is synonymous with IDE. "DMA" stands for
"Direct Memory Access" and refers to the controller's
ability to talk directly between memory and the disk drive without
bothering the computer's CPU. See also EIDE.
UltraSCSI - "Ultra Small Computer System
Interface" - An interface is used to connect a computer to
SCSI peripherals (hard drives, removable drives, printers, etc.).
UltraSCSI is an updated version of SCSI-2 which can transfer data at
20MBs on an 8-bit connection and 40MBs on a 16-bit connection.
Upstream - Refers to data flowing from the end user
back to the Internet service provider (usually in the case of
asymmetric transmission methods, such as ADSL)..
USB - Universal Serial Bus - An emerging
standard for (mainly) PC serial communications. USB runs at 12Mbs, and
supports up to 127 devices via a daisy-chain method. USB can
provide power from the computer's power supply to peripherals (so that
peripherals do not need their own AC power). USB
"hubs," boxes that provide multiple USB ports and a power
boost to the USB chain are usually needed if you have more than a few
USB devices on your machine. USB also allows hot-plugging so
that you can plug and unplug peripheral devices without having to shut
down your computer.
UUCP - "Unix-to-Unix Copy" - A suite
of programs and protocols that allow information to be passed between
Unix machines using serial connections. UUCP was invented at
Bell Labs in the late '70s to allow for the transfer of programs, data
files and email between Unix machines over standard telephone lines.
The Usenet newsgroups grew out of UUCP.
V.90 - The finally agreed-upon standard for 56Kbps
analog modems. Earlier competing standards, Rockwell's K56Flex
and 3COM's X2, are still widespread as consumers and service providers
upgrade to the new standard. Most 56K modems sold before the
standard approval can be software upgraded to V.90. The V.90
standard is likely to be the last analog modem standard, as cable
modems, DSL and other high-bandwidth connectivity schemes become more
prevalant.
WAP - "Wireless Access Protocol" - A
specification for wireless communication protocols. WAP is an
attempt to standardize the technology by which cell phones, radio
devices, wireless modems, and other similar devices access the
Internet so that these devices can interoperate. For more info,
check out the WAP Forum.
Wavetable synthesis - A sound technology that uses
samples of real instruments to create more realistic music playback.
For example, if a MIDI file calls for a particular instrument to play
a particular note, the computer (or MIDI instrument) accesses
the wavetable and chooses the appropriate note, pitch, etc.
Wavetable synthesis is, in most cases, much better than FM synthesis,
its predecessor.
Wiremap tester - Checks cables for wiring errors, such
as: open or short circuits, reversed pairs, crossed pairs, etc.
Wiremap testers may be complex digital devices, or simple analog
continuity-sensing devices.
XGA - "Extended Graphics Array" - A
high-resolution computer display standard developed by IBM in 1990.
XGA supports 65,536 colors at a screen resolution of 640 x 480 pixels
and 256 colors at 1,024 x 768 pixels. The latest, XGA-2, offers
1,024 by 768 resolution in high color and a higher-refresh rate than
XGA.
XJACK - A type of phone jack built into some laptop
PC-card modems. PC-cards are too thin to accept a conventional
RJ-11 phone plug. An XJACK is a horizontal jack that pops out
from the modem card, letting you vertically insert the RJ-11 plug.
XML - "Extensible Markup Language" - A
relatively new form of Web markup language (like HTML) that not only
tells the browser how to display the content on a page, but describes
the type of content. For example, a tag could be used to say
that a paragraph contains information on widgets for sale. A
shopping bot could then scour the XML pages on the Web and find who
has the cheapest widgets available. XML can be used to aggregate
any type of information on the Web. For more info, see the WC3's
page on XML.
Yagi antenna - A highly directional antenna containing
parallel antenna elements that reflect and direct the incoming signals
to the driven element (the part that is electrically connected to the
transmission line).
ZIF Socket - "Zero Insertion Force Socket"
- A type of socket that allows a computer chip to be installed
without the use of physical force (which can damage the pins on a
chip). A lever is used to press the socket's connecting parts
around the chip's pins, ensuring good electrical contact, and holding
the chip in place. ZIF sockets are found on most pre-Pentium II
motherboards, allowing average users to do processor upgrades.