Click on a letter to move to that section of the glossary.
D E F G H I J K L M N O P Q R S T U V W X Y Z
- A networking standard that utilizes UTP cabling with RJ-45 connectors, and transfers
data at up to 10 Mbps. It has the advantage of utilizing economical and easy-to-install
- A networking standard that transfers data at up to an amazing 100 Mbps, and utilizes UTP
cabling with RJ-45 connectors.
- Original Ethernet using coaxial cable.
- A networking standard that utilizes thin coaxial cabling with BNC connectors, and
transfers data at up to 10 Mbps. It has the advantage of utilizing cabling with longer
maximum lengths (610.5" as opposed to 330" with 10BaseT cabling).
- A technology that allows a serial port to transmit compressed data at up to 115.2 Kbps.
- A technology that allows a serial port to transmit compressed data at up to 460.8 Kbps.
- Defined by the IEEE (Institute of Electrical and Electronics Engineers), these standards
regulate the use of the CSMA/CD (Carrier Sense Multiple Access/Collision Detection network
access method used by Ethernet networks.
- The number of bits which represent each pixel, or point on the screen. An 8-bit per
pixel card can generate 256 colors; 24 bits per pixel yields 16.8 million colors.
- An IBM color monitor capable of resolutions of 720x400 non-interlaced with a refresh
rate of 70MHz; 640x480 non-interlaced at 60MHz; or 1024x768 interlaced at 43.58 MHz. All
of these resolutions are in 256 colors.
- A formula or procedure which employs various methods defining how data is to be used to
give a prescribed result.
- The variation in a sound signal producing varying levels of loudness. Measured in
- Analog Signals
- Signals which can vary over a continuous range (e.g., the human voice over conventional
telephone lines). Analog circuitry is more subject to distortion and noise, but it is more
capable of handling complex signals than are digital signals which can have only discrete
- Analog Sound
- Recorded sound depicted by fluctuations in amplitude.
- Automatic ReQuest for retransmission. A type of communications link where the receiver
asks the transmitter to re-send a block of data when errors are detected.
- American National Standards Institute. A non-profit, private industry association which
governs most USA-standards setting agencies.
- Acronym for American Standard Code for Information Interchange. ASCII is an ANSI
character set. The standard ASCII character set consists of 128 decimal numbers (0-127)
for letters of the alphabet, numerals, punctuation marks, and common special characters.
The extended ASCII character set extends to 255 characters and contains special
mathematical, graphics, and foreign characters.
- Asynchronous Communications
- A method of transmission in which one character is sent one bit at a time; also referred
to as serial transmission.
- AUI connector
- A networking connector that can be used with a transceiver to connect various kinds of
cables such as fiber optic (10BaseF), thick coaxial (10Base5), thin coaxial (10Base2) and
- auto-switching power supply
- An electrical plug that will work internationally in 110-, 220- or 230-volt outlets by
automatically detecting the current and using the appropriate voltage.
- Bell standards
- Refers to the U. S. modulation protocol standards developed by the former AT&T Bell
Systems such as Bell 103 (300bps transmission) and Bell 212A (1200bps transmission).
- Basic Input Output System. Provides fundamental services required for the operation of a
computer. Permanently present in the machine, these routines are generally stored in ROM
(Read Only Memory). The system board contains a ROM BIOS to support all of its standard
functions. The Voyager Movie Player also has a BIOS for display features.
- Bit Block Transfer
- A method of holding a block of graphics, such as Windows dialogue box, in memory so that
it can be moved and redrawn quickly by memory-to-memory operations.
- Bit-mapped Registers
- An S-register which contains multiple bit-oriented values.
- Blind Dialing
- An automated process whereby the modem goes off-hook and dials without waiting for a
dial tone. This is prohibited in many countries.
- Block Transfer Control
- Determines whether or not the modem uses block or stream mode during an MNP connection.
In stream mode, MNP sends data frames in varying length. Block mode sends fixed data
frames of 256 characters.
- BNC connector
- A connector utilized in 10Base2 networks with thin coaxial cabling.
- Boot PROM
- (Boot Programmable Read-Only Memory). A ROM chip usually mounted on the network
interface card that enables a personal computer to load the operating system from the
- Bits per second.
- Break Handling
- Determines how the modem responds when a BREAK signal is received from either the DTE
(Data Terminal Equipment or computer/terminal) or the remote modem. This is controlled by
the MNP-based AT extended commands. A break signal is represented on the communications
line by a steady space signal for a significant length of time. Break signals may be
activated from the keyboard by pressing the BREAK key or the control (CTRL) and C keys.
- Bus topology
- A network topology in which nodes are connected to a single cable with terminators at
- Consultative Committee for International Telephone and Telegraph. This advisory
organization is part of the ITU (International Telecommunication Union) which is an agency
of the United Nations. Organization recently renamed International Telecommunications
Union-Telecommunications Standard Sector (ITU-T)
- CD Quality
- Recording quality similar to that of a compact disc player. This means that 16 bits of
information are recorded for every sample taken. See Bits Per Sample and Sampling.
- Color Graphics Adapter. Medium resolution IBM graphics standard capable of displaying
640 x 200 pixels in 2 colors, or 320 x 200 pixels in 4 colors.
- Coaxial Cable
- Data transmission medium with a single-wire conductor insulated from electro-magnetic
and radio frequency interference.
- Command Mode
- The modem is in command mode when it is turned on or reset, when it loses its connection
to a remote modem, when it is in on-line mode, or when escape characters (+++) are typed.
To transmit data, the modem must be in data mode. The modem does not transmit data when in
- Communications Protocol
- A set of procedures which controls how a data communications network operates.
- See hub.
- Carrier Sense Multiple Access with Collision Detection. CSMA/CD is the access method
used in Ethernet where nodes contend for the right to send data.
- Data Carrier Detect. Indicates to the terminal device that the modem is receiving a
valid carrier signal from a remote modem. The carrier is a tone at a specified frequency.
- Data Communications Equipment. The local and/or remote modem. A DCE is usually connected
to a DTE.
- Direct Memory Access. DACK stands for Dma ACKnowledge and DRQ for Dma ReQuest. DMA
provides direct access to system memory without adding to CPU overhead. The DACK and DRQ
channels govern that communication.
- Data Terminal Equipment. The computer or terminal, either local (yours), or the remote
(the one you're communicating with). A DTE is usually connected to a DCE.
- Dynamic RAM. RAM is random access memory.
- Data Terminal Ready. The computer issues this signal to the attached modem indicating
that it is ready to receive data.
- Data Compression
- A technique that examines transmitted data for redundancy and replaces strings (groups)
of characters with special codes which the receiving modem interprets and restores to its
original form. Transmission of compressed data results in shorter connect times and hence
cost savings for connect charges. Data compression is sometimes called "source
- Data Mode
- The modem is in data mode when a connection has been established with a remote modem and
sends a CONNECT response confirming the connection. User data may then be transmitted or
- Decibel (dB)
- A means of measuring amplitude.
- Dial Modifier
- Dial modifiers are special characters appended to the ATD command which instruct the
modem how to place a call.
- Digital Signal
- A discrete signal which can only take on one of several (usually only two) discrete
levels in contrast to analog signals which can take a continuous range of levels.
- Digital Sound
- Recorded and stored sound as a series of numerical values rather than fluctuations in
- dual-line modem
- A modem with two 56K modem chips on a single board that connects to two regular phone
lines and utilizes bonding software to offer transmission speeds of up to 112 Kbps.
- Enhanced Color Display. An EGA specification. TTL monitor capable of displaying video
signals with horizontal scan frequencies of 15.750KHz (CGA) or 21.850KHz (EGA) only.
- Enhanced Graphics Adapter. High resolution IBM graphics standard capable of displaying
640 x 350 pixels in 16 colors out of a palette of 64 colors.
- Error Detection and Correction.
- The transmitting modem attaches a special pattern (called a frame check sequence)
calculated according to a prescribed algorithm from user-defined data to the end of a
block of data. The receiving modem performs the same algorithm and compares it to the one
with the transmitted data. If these match, then the block of data has been received
correctly. If not, the block of data is re-transmitted until no errors are detected.
- Escape Sequence
- Also referred to as the escape command. This special command is entered as three plus
symbols (+++) and places the modem in command mode and interrupts user data transmission,
but does not terminate the data connection. This allows the entering of commands while the
connection is maintained.
- A 10 megabits-per-second baseband, CSMA/CD network originally designed by the Xerox
- Extended AT-Command
- Extended commands were developed to provide greater functionality and control over modem
operations than is available from the basic AT command set.
- Fax Mode
- The modem is in fax mode when, through use of fax communications software, it can send
and receive faxes, print and display fax files, convert files to fax-files, and set
certain fax-related features. Note: the modulation protocol used by the modem in fax mode
is also different from the usual data mode modulation.
- Feature Connector
- Used by graphics adapters to give compatibility with VGA text and graphics codes for use
with multi-media applications.
- File Server
- A device on a LAN that provides mass storage of files. A file server can be dedicated
(only performs network management functions) or non-dedicated (where user applications can
co-exist while the network is available.
- Flow Control
- Compensates for the difference between the rate at which data reaches a device and the
rate at which the device processes and transmits. The two common types of flow control are
RTS/CTS signaling (a hardware based method, employing an electrical signal) and XON/XOFF
(a software-based method using standard ASCII control characters to pause or resume
transmission). The \G command controls XON/XOFF flow control.
- full duplex
- The ability to send and receive data at the same time. (A full duplex speakerphone
allows you to hear what is going on at the other end of the line while you are talking.)
- Guard Tone
- Guard tones are used in the United Kingdom and other countries. This requires that the
modem transmit an 1800-Hz tone after it sends an answer tone. The guard tone is controlled
by the &G command. Guard tones are not used in the U.S.A.
- Graphical User Interface.
- half duplex
- The ability to send data in only one direction at a time.
- Hayes Microcomputer Products, Inc. developed the AT command set which has become a de
facto industry standard. Hayes commands are always initiated with an AT (attention code)
- Hardware Graphics Cursor
- Provides a faster method of displaying/moving a cursor (GUI arrow) on the screen. The
video adapter's main chipset controls this function which resides in system memory, as
opposed to slower handling by the application software.
- Hercules Graphics Card. Compatible with MDA, but also capable of displaying 720 x 348
pixels in a 4-bank graphics mode.
- Short for High Resolution, this term should be only applied to a minimum of 640 x 350
resolution and above.
- Hook Flash
- The dial modifier "!" causes the modem to go on-hook (hang-up) for one-half
second. Also controlled by the ATH command.
- Horizontal Scan Rate
- The frequency in KHz (kilohertz) at which the monitor is scanned in a horizontal
direction; high horizontal scan rates produce higher resolution. The EGA horizontal scan
rate is 21.8 KHz, while the extended EGA horizontal scan rate is 30.1 KHz.
- A networking device with multiple ports that allows you to connect workstations, servers
or peripherals to a network.
- IEEE 802.3 compliant
- Complying to the standards for 10 Mbps networks established by the Institute of
Electrical and Electronic Engineers (IEEE)
- A method of scanning a screen which results in alternate lines being drawn with each
full pass of the electron beam. The resulting display is less stable than a flicker-free
- I/O card
- An abbreviation for input/output card. A board in your PC with a serial or parallel port
that allows you to connect peripherals to your computer. I/O cards can also have multiple
serial or parallel ports or a combination of both.
- This occurs when there are excessively long data packets being transmitted from the node
(i.e., workstation, server). At that point, the hub, or concentrator, partitions
(isolates) the node from the network until the condition is corrected.
- jabber protection
- A feature of some networking hubs that ensures your network won't go down due to
excessively long data packets.
- A set of tiny switches used to select one of various options such as a particular
- An abbreviation for kilobits per second. A measurement of the transmission speed of data
measured in 1,024 bits per second.
- (Local Area Network) A data communications network confined to a limited geographic
area, with moderate to high data rates (100kbps to 100Mbps). The area served may consist
of a single building or campus-type arrangement. It is owned by it's use, includes some
type of switching technology, and does not use common carrier circuits - although it may
have gateways or bridges to other public or private networks.
- Link Access Protocol Modem. A V.42 ARQ type of error correction protocol where LAPM may
be activated with or without V.42bis data compression.
- Leased Line
- Also referred to as a private line. A leased line is obtained from a communications
company (carrier) to provide a transmission medium between two points. The line consists
of a permanent dedicated circuit between two points, or to set of previously arranged
points. The cost of the line is usually based on the distance between locations. This is
in contrast to switched or dial-up lines, which can be connected to any point on the
- Light-emitting diode.
- Line Modulation
- The means by which a carrier is varied to represent a signal carrying information. In a
modem, the user's digital data is used to modulate the modem's transmitter's carrier or
carrier to allow the digital signal to be carried over analog facilities.
- A connector on audio equipment to which a device like a CD-player or tape cassette
player may be attached. See also Line Out.
- A connector on audio equipment to which audio components can be attached such as stereo
speakers. See also Line In.
- Long Space Disconnect
- Determines whether or not modem disconnects when it receives a continuous break from a
remote modem. Controlled by the ATY command.
- Loopback Tests
- There are four types of loopback tests which are as follows: (1) the local digital
loopback tests the operation of the DTE, including whether or not data is leaving the
terminal or computer port; (2) the local analog loopback tests the digital and analog
circuits of the modem; (3) the remote digital loopback checks the operating condition of
the line and remote modem; (4) the remote analog loopback tests the line to the remote
- Make/Break Ratio
- The &P command controls the ratio of the off-hook (make) to on-hook (break) interval
used by the modem when it pulse dials. &P0 selects a 39%/61% make/break ratio for use
in the U.S. &P1 selects a 33%/67% make/break ratio for use in the United Kingdom and
Hong Kong. The &P command is NOT allowed in some countries.
- Monochrome Display Adapter. Early IBM Video display board designed for use with IBM
monochrome text standard.
- Musical Instrument Digital Interface. A standard which allows for the exchange of data
between two music synthesizers or a synthesizer and a computer. Sound data may be
communicated from the synthesizer to the computer and stored as a MIDI file. Or, a MIDI
file can be transmitted to the synthesizer for playback.
- Microcom Networking Protocol. A series of data communications protocols developed by
Microcom for full-duplex, error-free communications.
- Modulation Handshake
- Also referred to as Automode Enable and is controlled by the ATN command. This
determines whether or not the modem must connect at a particular speed, or allow
connection at any speed supported by both modems.
- A UART on the MIDI port which allows MIDI interface to transmit and receive at 32.5K
baud (see Appendix E for more information).
- (Motion Pictures Expert Group). A type of data compression storage and playback of video
and audio data.
- An abbreviation for megabits per second. A measurement of the transmission speed of data
measured in 1,048,576 bits per second.
- Multiple Frequency Monitor
- Monitor capable of displaying video signals over a wide range of horizontal scan
frequencies. This may include a horizontal capture range from 5.5KHz to 35KHz or wider.
Examples of monitors in this class are the NEC MultiSync and the Sony Multiscan. The
Multiscan has a wide horizontal scan capture range which enables it to display monochrome
- Negotiation Fallback
- Controlled by S-Register 36 as part of the V.42 protocol. Setting this register
indicates what action to take when a desired connection cannot be made (e.g., hang-up,
direct mode connect, normal mode connect).
- network adapter card
- A board in your PC that has one or more ports for connection to a network.
- Network topology
- The arrangement of nodes usually forming a star, ring, tree, or bus pattern.
- Any device including servers and workstations connected to a network; also the point
where devices are connected.
- Non-Volatile RAM
- Also NVRAM. Random access memory whose data is retained when power is turned off. This
is especially useful for modems to store user-defined default configuration settings and
frequently used telephone numbers. This information would be loaded into modem RAM at
- On-Line State
- Same as data mode. To transmit or receive data, the modem must be in the on-line state.
When placing a call, the modem is put on-line with the dial command.
- A collection of bits comprising data and control information formatted for transmission
from one node to another.
- The range of colors from which you can select the actual colors that the video adapter
will display simultaneously.
- parallel port
- One of several kinds of connectors found on the back of computers used to connect
peripherals. Peripherals that connect to parallel ports include printers, Zip drives, tape
drives and CD-ROM drives.
- Private Branch Exchange. A telephone switch at a customer site.
- A sound's tone, usually determined by the sound's frequency
- A single dot on the CRT display. This word is derived from the words 'picture' and
- Plug and Play
- An industry-wide standard for add-on hardware which indicates that it will configure
itself, thus eliminating the need to set jumpers, and making installation of the product
quick and easy.
- A standardized set of rules that specify the format, timing, sequencing, and/or error
checking for data transmissions.
- Pulse Dialing
- Also referred to as rotary dialing, i.e., dialing with the older-style rotary dial
wheel. The dial modifier ATDP sets the modem to pulse dialing, which is the default method
as opposed to tone dialing (push-button touch-tone) which is enabled with ATDT. All
telephone exchanges will accept older-style pulse dialing and most exchanges will accept
modern tone-dialing. Tone dialing is faster and more reliable since mechanical relays and
their inherent failure mechanisms are avoided.
- RAM Digital to Analog Converter.
- Refresh Rate
- Also called Vertical Scan Rate, the speed at which the screen is repainted. Typically,
color displays must be refreshed at 60 times per second. Usually, the faster the refresh
rate, the less flicker a monitor has (normally defined in Hz).
- Register Level Compatibility
- Complete compatibility to the hardware level.
- Used to extend the topology, allowing two or more cable segments to be joined. In a
10Base-T network, the repeater provides the central connection point where the gathering
of statistics and network management functions take place.
- Result Code
- A response sent by the modem after executing a command. The response reports the modem's
status or the progress of a call and can take the form of either digits (numeric) or words
(verbose). Issuing a V1 command enables word responses. A V0 (V-zero) command enables
numeric responses. The Q1 command disables their use entirely. Example: "OK"
(word), or 0 (numeric) indicates that the modem successfully executed a command.
- An adjustment process performed when one of the modems detects signal distortion or line
noise which threaten data integrity.
- RGB Monitor
- Red/Green/Blue. A CGA compatible monitor limited to a 15.750KHz horizontal scan rate.
- Ring Topology
- A network topology in which nodes are connected in a closed loop; no terminators are
required because there are no unconnected ends.
- RJ-45 connector
- A connector utilized in 10BaseT and 100BaseTX networks with UTP cabling.
- Request to Send/Clear to Send. RTS and CTS are two control signal lines between the
modem (DCE) and terminal (DTE) which allow the terminal to control the flow of
information. See also flow control.
- A measurement of sound taken during a certain duration. In digital recording, sampling
means recording voltages which make a sound as a sequence of numerical values representing
the sound's amplitude.
- Scan Rate
- The frequency in Hertz (Hz) at which the monitor is scanned horizontally. Generally, the
higher the scan rate, the higher the resolution.
- serial port
- One of several kinds of connectors found on the back of computers used to connect
peripherals. Peripherals that connect to serial ports include external modems, ISDN
terminal adapters and mice.
- A computer that provides shared resources, such as files and printers, to the network.
- Sleep Inactivity Timer
- Determines the length of time the modem operates in normal mode with no activity before
entering low-power "sleep" mode.
- software configurable
- The ability of an add-on product to be configured by its software, thus eliminating the
need to set jumpers, and making installation of the product quick and easy.
- Sound File
- Any file which holds sound data. Examples: files with .MID file name extensions are
compatible with the MIDI standard (see above); a file with a .WAV file name extension is a
standard Microsoft file format for storing waveform audio data. See Waveform and wave
- Split-Speed Direction
- Determines which direction (transmit or receive) has the 75bps channel and which has the
- Standard AT-Command
- The basic AT command set, originated by Hayes Microcomputer Products, Inc.
- Star Topology
- A network topology in which nodes are connected to a common device such as hub or
- Synchronous Communications
- A method of transmission in which data bits are sent continuously at the same rate under
the control of a fixed frequency clock signal.
- A T-shaped device with two female and one male BNC connectors.
- 50-ohm coaxial plug used to attach to one end of a BNC T-connector when the associated
station is first or last in the group.
- thin coaxial cable
- A networking cable with BNC terminators used on 10Base2 networks.
- How the ear identifies and classifies sound. Example: the timbre of the same note played
by two different instruments (flute and tuba) will not be the same.
- Touch-Tone Dialing
- Push-button tone dialing as used on contemporary phone sets. The dial modifier ATDT sets
the modem to "tone" mode. Tone dialing is faster and more reliable than
older-style pulse dialing.
- The physical layout of a network. The principal LAN topologies are bus, ring, and star.
- An AUI (Attachment Unit Interface) device for receiving and transmitting data that often
provides collision detection as well.
- Trellis Coding
- A method of modulation which targets specific modulation points. Signals falling outside
of these points are treated as line noise, thus ensuring greater noise immunity over a
given line. QAM (Quadrature Amplitude Modulation) functions similarly, but has a broader
tolerance and results in lesser noise immunity than trellis coding.
- Terminate and Stay Resident. A program that remains in memory after it has been loaded.
- Transistor-Transistor Logic; a fast, reasonable-cost type of integrated circuit used in
- TTL Monitor
- Video and synchronization signals (all digital) are on separate lines and have TTL
compatible voltage levels
- Twisted-Pair cable
- A wiring scheme with one or more pairs of 18 to 24- gauge copper strands.
- UTP cable
- An abbreviation for unshielded twisted-pair cable. A networking cable with RJ-45
connectors used on 10BaseT and 100BaseTX networks.
- Video Electronics Standards Association.
- (Video Graphics Array) Analog graphics standard introduced with the IBM PS/2 series.
Backwards compatible with EGA at the BIOS level, but provides higher resolutions. Supports
a maximum resolution of 640 x 480 pixels in 16 colors out of a palette of 262,144 colors.
- Voice Annotation
- Embedding of a voice message into a document for later playback.
- A modem standard established by the ITU which assures that 56K modems that comply with
the standard will be able to communicate with one another regardless of the manufacturer
of the modem.
- (Wide-Area Network) A network which uses common carrier-provided lines; contrast with
- Wave File
- A standard Microsoft file format for storing waveform audio data.
- A graph showing the amplitude of a sound over a particular interval of time. Any portion
of that interval is a sample.
- XON and XOFF are the names of two different flow control characters. See also flow