Specifications

MultiModem ISI Hybrid Series, ISIHI-2S/2U 177
Glossary
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
parameters 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 interact.
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.
(data terminating equipment)A term used to include any
device in a network that generates, stores, or displays user
information. DTE is a telecommunications term that 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 alphanumeric
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 outstanding
contributions in electronics, and sets electronic interface
standards, such as RS-232.
EISA (Enhanced Industry Standard Architecture, pronounced
eesa)The purpose of the EISA bus was to provide a 32-
bit bus for faster throughputs while maintaining backward
compatibility with the classic ISA bus architecture.
emulationThe process of one type of device imitating
another via a hardware or software package. Terminal
emulation, for example, allows a PC to access a mainframe
computer by generating and accepting data like a dumb
terminal.
environmentA computer configuration that includes the
CPU model and system software (operating system, data
communications and database systems). It may also include
the programming language used. It sets the standards for the
applications that run in it.
EPROM (erasable programmable read only memory,
pronounced eeprom)A reusable PROM chip that holds its
contents until erased under ultraviolet light.
error correctionThe process of detecting distorted data
bits and requesting a retransmission or interpretation to
correct the error. Errors are introduced by bad line condi-
tions or external interface.
F
fax (facsimile)Refers to the bit-mapped rendition of a
graphics-oriented document (fax) or to the electronic
transmission of the image over telephone lines (faxing). Fax
transmission differs from data transmission in that the
former is a bit-mapped approximation of a graphical
document and, therefore, cannot be accurately interpreted
according to any character code.
fax cardAn expansion card that, with the appropriate
software, allows a PC to operate as a fax transmitter/
receiver. PC fax cards may be able to send and receive
faxes from a file on the PC. If an external scanner is
available, the PC can also transmit the scanned image via
the fax card.
fax/data modemA multifunctional device capable of
transmitting either data or faxes. It is available as an
external unit or expansion board. It includes a fax switch
that routes the call to the fax or the data modem.
fax serverA network resource that allows workstation PCs
to transmit faxes as though the PC had an internal fax card
or a fax modem attached.
firmwareA category of memory chips that hold their
content without electrical power. They include ROM,
PROM, EPROM, and EEPROM technologies. Firmware
becomes hard software when holding program code.
flash memoryA memory chip that holds its content without
power, but must be erased in bulk. The term comes from its
ability to be erased in a flash. Flash memory is derived
form EEPROM, but is less expensive and provides higher
bit densities.
floppy diskAlso called a diskette. It is a round disk with a
hole in the middle, made of flexible material and housed in