H

hard copy

Printed information, as opposed to information displayed on a video screen.

hardware

Computers, printers, disks, and other devices whose fundamental characteristics were determined at the time of manufacture. Changes in such devices require the use of tools. Contrast with firmware and software .

HDLC

Hierarchical Data Link Control, a data link layer protocol in which data is transmitted with a zero inserted after each consecutive group of five 1s, except for a distinctive ?flag? pattern (01111110), which delineates the beginning and end of a frame. This protocol is very similar to SDLC, but the header is arranged to allow for longer addresses and longer message numbers.

headend

In a CATV system, apparatus located near the receiving antenna and used to amplify and otherwise condition the received signals for transmission over the cabling system to subscribers? homes. In a broadband local area network utilizing a single cable, apparatus that translates the frequencies used for transmission of data onto the cable into the frequencies used for reception of data from the cable. In a broadband local area network utilizing two cables, a loop of cable that connects the cable used for transmission of data to the cable used for reception of data.

header

That portion of a message, at the beginning, which contains destination address, source address, message numbering, and other control information.

Hertz (Hz)

A unit of frequency equal to one cycle per second. Named in honor of Heinrich Hertz.

host

A computer system that provides computational...

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