Specifications

180 MultiModemISI Hybrid Series, ISIHI-2S/2U
Glossary
circuit board that provides the physical and electrical
connection between a PC and a network device (like a file
server) via a network media (like Arcnet UTP).
nodeAny point within a network that has been assigned an
address.
normal modeIn modem operation, this refers to a mode of
operation without error correction active.
O
OCR (optical character recognition)The recognition of
printed characters and subsequent translation into character
code for use on a computer. OCR systems can recognize
many different fonts, as well as typewriter and computer-
printed characters. Advanced OCR systems can recognize
hand printing.
off-hookThe condition of a device that has accessed a
phone line (with or without using the line). In modem use,
this is equivalent to a telephone handset being picked up.
Dialing and transmission are allowed, but incoming calls
are not answered.
OS (operating system)The master control program that runs
a computing system. It is the first program loaded when the
computer is turned on. Its main part is called the kernel and
resides in the memory at all times.
P
parameter1. A place holder in a command that should be
substituted with useful information. 2. The list of acceptable
values for a given option or command.
parity bitAn extra bit attached to each byte of synchronous
data used to detect errors in transmission.
PCB (printed circuit board)A flat board that holds chips
and other electronic components. The board is printed with
electrically conductive pathways between components. The
main PCB in a system is called a motherboard and the
smaller PCBs that plug into the slots in the motherboard are
called daughter boards or cards.
PCMCIA (Personal Computer Memory Card International
Association)An organization of U.S. and Japanese
companies set up to standardize memory cards and other
architecture-independent expansion devices. These cards
typically are used in laptop computers.
phaseThe timing of a signal based upon the starting point
of each cycle in another signal. To be detected, phase
requires the comparing of two signals. If the cycle of two
signals begin at the same point, they are said to be in-phase.
In-phase signals add, while out-of-phase signals tend to
cancel each other.
portA location for input or output data exchange. Comput-
ers, muxes, etc., have ports for various purposes.
print serverA computer in a network that controls one or
more printers. It stores the print image output from all users
of the system and feeds it to the printer one job at a time.
The print server may be part of the network operating
system or an add-on utility.
programA collection of computer instructions that tell the
computer what to do.
PROM (programmable read only memory)A permanent
memory chip that can be programmed or filled by the
customer after the manufacturer sets initial values. Contrast
with ROM.
promptA request for information from the PC that provides
required input or information.
protocolA set of rules that defines how computing devices
communicate with each other. The rules governing the
transmitting and receiving of data.
PSK (phase shift keying)A modulation technique that
establishes two-bit elements, called dibits, yielding four
possible combinations: 00,01,10,11. These elements then
are represented by 90, 180 and 270 degree angles. PSK
produces the appropriate shift in phase relative to the
original carrier. Differential PSK replaces this technology
because it is less prone to error. Modems using PSK
normally operate at 1200bps.
PSTN (Public Switched Telephone Network)A worldwide
public voice telephone network that is used as a telecom-
munications medium for the transmission of voice, data and
other information.
pulse dialingOne of two methods of dialing a telephone,
usually associated with rotary dial phones. Compare with
tone dialing.
pulse-widthPertaining to a digital signal. Pulse width
refers to the duration of one state between clocking signals.
Pulse width roughly corresponds to an analog signals
wavelength.
Q
QAM (quadrature amplitude modulation)A complex
method of modulation that establishes twelve phase angles
and four amplitudes, designating sixteen possible combina-
tions. QAM encodes hexadecimal values (also called
quadbits) into one cycle of the carrier. Using a 1800bps
carrier frequency and a 2400 baud signaling rate, QAM
provides a 9600bps modulation speed. However, because it
uses amplitude modulation, QAM is susceptible to noise.
queueA set of activities that are waiting in chronological
order for an action, such as printing, to be performed.
R
rackA frame or cabinet into which components are
mounted. The industry standard rack is 19" wide and has
variable depth and height.
rackmountA packaging style available for many types of
electronic equipment which enables the installer to mount
the equipment in an industry standardized enclosure.
Rackmount equipment is fitted with brackets, rather than
being packaged in its own enclosure. Rackmounting
conserves disk and floor space (real estate) and often
conserves power outlets.
RAM (random access memory)A computers primary
workspace. All data must be stored in RAM (even for a
short while) before software can use the processor to