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.