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Glossary
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Header
In communications protocols, this is the control information that precedes the message or text
portion of a block of data.
Hertz (Hz)
Unit of frequency, one cycle per second.
Horizontal Redundancy Checking (HRC)
Technique in which redundant information is included with a block of data for validating the
transmitted data at the receiving end.
Host Computer
A computer that manages information for many terminals. A host computer may be mainframe,
minicomputer or a microcomputer.
I
ID Name
See ID Number.
ID Number
A security code, used mainly with remote systems that either charge a subscription fee, allow
the purchasing of goods and services on line or both. The code is known only to the user and
protects the user from unauthorised access to her/his account. See also Password.
Input
Information transferred into a computer from some external source, such as the keyboard, a disk
drive, a modem or a scanner. Also, the act or process of transferring such information.
Input/Output Device
A device that transfers information into or out of a computer.
Interface
A physical point of interconnection between two devices where electrical signal levels, timing,
handshaking and pin numbers are defined. The devices, rules or convention by which one
component of a system communcates with another.
Interference
Undesirable disturbances or distortions in a data transmission signal.
Intermediate Page
An index page which, when used with another index page, allows users to perform double-digit
keying.