Multi Tech Equipment ISIHI-2S manual DOS prompt The symbol displayed after the disk drive letter

Glossary

Data compression: The process of reducing the data bits necessary to represent useful information. By compressing files, less storage is required and higher throughputs are realized.

Data Pump: The DAC (Digital-to-Analog Conversion) circuitry used within a modem.

DB-25: A very common 25-pin connector often referred to as an RSs-232 connector because it is the connector over which the RS-232 interface commonly occurs.

DB (Direct Current): Usually understood to mean a constant voltage supply that fluctuates only a nominal amount. An analog or digital signal that may vary in voltage level, but it never crosses the reference voltage (usually called ground). Contrast with AC>

De facto standards: A de facto standard is one of two types of voluntary standards recognized by a given market. It is introduced by a single vendor and becomes a standard by its widespread use and acceptance by other vendors. AT&T’s Bell 212A, IBM’s Binary Synchronous Protocol, or DEC’s VT-100 terminal protocol are examples of de facto standards. Compare with de jure standards.

De jure standards: A de jure standard is one of two types of voluntary standards. It represents the collective consen- sus of the industry and users for a particular aspect of manufacturing. CCITT’s V and X standards (V.32 and Xx.25) are examples of de jure standards. Compare with de factor standards.

Decibel (dB): A unit of measurement for signal strength based on logarithmic increments, A decibel is a relative measurement that is derived from an initial reference level and a final observed level.

Default: A preset value or option, in software packages, or in hardware configuration, that is used unless you specify otherwise.

Device driver: Software that controls how a computer communicates with a device, such as a printer or mouse.

Digital signal: Digital devices, such as terminals and computers, transmit data as a series of electrical pulses that have discrete jumps rather than gradual changes.

Digital Transmission: A method of electronic information transmission common between computers and other digital devices. Analog signals are waveforms: a combination of many possible voltages. A computer’s digital signal may be only “high” or “low” at any given time. Therefore, digital signals may be “cleaned up” (noise and distortion removed) and amplified during transmission.

DIP switch: A set of tiny toggle switches, built into a DIP (dual in-line package), used for setting configurable param- eters on a PCB (printed circuit board).

Directory: A logical subdivision of a computer’s disk space used to organize a group of files. A directory can be thought

of as a file drawer.

DOS (Disk Operating System - pronounced “daws”) : The software that allows all the hardware in a PC to inter- act. The basis for (DOS prompt) higher level applications.

DOS prompt: The > symbol displayed after the disk drive letter.

DPSK (Differential Phase Shift Keying): A common form of phase modulation used in modems. It does not require complex demodulation circuitry and is not susceptible to random phase changes in the transmitted waveform, thus reducing errors during transmission.

Driver: A software module that interfaces between the Operating System and a specific hardware device, such as a color monitor, printer or hard disk. Also known as a device driver.

DSR (Data Set Ready): An RS-232 signal sent from the modem to the computer or terminal indicating that it is able to accept data. Contrast with DTR.

DTE (Data Terminating Equipment): A term used to include any device in a network which generates, stores, or displays user information. DTE is a telecommunications term which usually refers to PCs, terminals, printers, etc.

DTMF (Dual-Tone MultiFrequency): A generic push-button concept made popular by AT&T TouchTone.

DTR (Data Terminal Ready): An RS-232 signal sent from the computer or terminal to the modem indicating that it is able to accept data.

E

EBCDIC (Extended Binary Coded Decimal Interchange Code - pronounced “eb suh dick”) : An IBM character code used in its mainframe and midrange computers. It is an 8-bit code (256 combinations) that stores one alphanu- meric character or two decimal digits within a byte. EBCDIC and ASCII codes are the most common codes used to represent data.

Echo: The reflection or duplication of a signal back toward its source. Echoing is useful when a terminal is transmitting data, in that the data can be echoed to the screen so the user can monitor what is being sent. Echoing is undesirable when it refers to the signal which results on a telephone line from impedance mismatches.

Echo cancellation: a high speed modem technique that isolates and filters out unwanted signals caused by echoes from the main transmitted signal. This allows full-duplex modems to send and receive on the same frequency carrier.

EIA (Electronics Industries Association); A membership organization founded in 1924 that includes manufacturers of electronic parts and systems. With over 1200 members, it sponsors shows and seminars, gives awards for outstand-

MultiModemISI Hybrid Series, ISIHI-2S 173