H

H

Hexadecimal

HA

IC part number prefix indicating Harris Semiconductor.

HAL

Hardware Abstraction Layer - part of Windows NT

HALF DUPLEX

Biderectional transmission but not simultaneously

HALF-DUPLEX

A two-way data transmission mode where data between two points is sent one direction at a time.

HALO

The black border around exceptionally bright objects in an image.

HANG UP

To end a LAN Distance connection.

HARD DISK PARTITION TABLE VIRUS

The first physical sector of a hard disk on a PC contains the partition table program. When a computer is booted from a hard disk, the BIOS loads and executes the partition table program. This program first determines which disk partition is the active partition. It then loads the boot sector from the active partition and executes it. As with viruses that infect boot sectors, partition table infectors copy the partition table program to another location on the disk, then copy their code to the sector normally containing the partition table. The BIOS loads and executes the virus during the boot process, after which the virus executes the copy of the partition table program it has saved elsewhere. A virus that infects only partition tables could not spread from one computer to another, so partition table infectors must also infect boot sectors or executable files.

HARDWARE

Starts out working OK, but as it gets older, more and more things go wrong. See Software.

HAYES AT COMMAND SET

See CCITT V.25BIS.

HAYES COMPATIBILITY

Software (and people) communicate with modems using the AT command set originally developed by Hayes Corporation. Modems that use the AT command set are said to be Hayes-compatible.

HBT

Heterojunction Bipolar Transistor

HDLA

High Level Design Automation

HDLC

See High-level Data Link Control.

HDLC

See High-Level Data Link Control.

HDTV

See High Definition TV.

HDX

See two-way alternate (half-duplex). See Half DupleX.

HEADER

A series of lines at the beginning of an article or electronic mail message that contain such information as the article's or message's author, its subject, its date and time of transmission, and so on.

HEARTBEAT

Ethernet defined SQE signal quality test function.

HELLO PROTOCOL

A protocol the OSPF routers use to maintain reachability.

HELLO/I-H-U

Hello and I-Heard-You. An EGP protocol that requests and confirms

HETEROGENEOUS CACHE

Contains different types of data formatted in different ways by different applications. Can be thought of as an aggregate of homogeneous caches.

HEXADECIMAL

A base-16 numbering system that uses the symbols 0,1, 2, 3, 4, 5,6, 7, 8, 9,A, B, C, D,E, F.

HFC

Hell Fire Club

HIGH BYTE

The 8 most-significant bits of a 16-bit word.

HIGH DEFINITION TV

A proposed standard, recommending the doubling of the current 525 lines per picture to 1050 lines and increasing the screen aspect ratio (width:height) from the current 12:9 to 16:9, which would create a television screen shaped more like a movie screen.

HIGH MEMORY AREA

HMA refers to a specific way of accessing the first 64Kb of Extended Memory, into which MS-DOS, drivers and utilities can be loaded to save conventional memory. Normally, for an 80286 to access extended memory, the processer has to switch into what is called "protected mode", make the extended memory access, and then be reset so that it returns to "real mode" (which is the mode that DOS runs under). This whole operation takes time. There is, however, a "back door" method to access the first 64K of extended memory without switching the processor into protected mode. What manages this special way of accessing the first 64K of extended memory is something called an HMA provider (also sometimes called an A20 handler). See Extended Memory.

HIGH NIBBLE

The 4 most-significant bits of a byte.

HIGH PERFORMANCE PARALLEL INTERFACE

(HIPPI) is a LAN standard that the ANSI X3T9.3 committees currently are investigating to provide data rates between 800 Mbps to 1600 Mbps. HIPPI transfers 32 bits of data in parallel across distances of about 25 meters. The parallel transmission runs over a 50-pair twisted pair wire cable--32 pairs are used for data lines and the remaining lines are used for control. HIPPI evolved from the proprietary HSX I/O bus that CRAY supercom-puters use. Graphic workstations require high I/O data rates to perform real-time modeling and display. The HIPPI standard proposes a HIPPI Framing Protocol Layer that allows IEEE 802.2 protocol to run on top of it. Any protocol stack that uses IEEE 802.2, such as NetWare, can make use of HIPPI.

HIGH RESOLUTION

An adjective describing improvement in image quality as a result of increasing the number of pixels per square inch. Called hi-res for short.

HIGH SIERRA FORMAT

A standard format for placing files and directories on CD-ROM, revised and adopted by the International Standards Organization as ISO 9660.

HIGH-LEVEL DATA LINK CONTROL

(HDLC) is a bit-oriented, full-duplex ISO standard. This protocol is widely used and is an OSI layer two (data link layer) frame format. Packets or frames can be encapsulated into HDLC frames for analog or digital transmissions. Most proprietary synchronous protocols either use or are based on HDLC. Many vendors have improved HDLC to refine protocols used in their own equipment. This, of course, means that their equipment is not interoperable with other vendors' equipment, which is generally the case.

HIPPI

See High Performance Parallel Interface.

HLLAPI

High Level Language API

HMA

See High Memory Area.

HMD

Head Mounted Display

HMI

Human-Machine Interface

HMP

Host Monitoring Protocol

HOLDING TIMER

An OSI configurable timer that informs an ES or IS how long it is to retain the information contained in the hello message.

HOMOGENEOUS CACHE

Contains information structured in a consistent manner under the control of a single application.

HOMOLOGATION

The enforcement of certain country or network requirements regarding the use of telephone circuits and other networks by computers. The LAN Distance product requires the modems that it uses to be homologated.

HOOK FLASH

The act of hanging up the telephone for a short period of time (one-half second). This operation is useful in PBX systems that interpret a hook flash as a signal to perform other services, such as transferring a call.

HOOKSWITCH

The switch controlled by the telephone handset, which closes its contacts when the handset is lifted from its mounting and opens its contacts when the handset is replaced on its mounting.

HOP COUNT

A measure of distance between two points in the Internet. Each hop count corresponds to one router separating a source from a destination (for example, a hop count of "3" indicates that three routers separate a source from a destination).

HOPS

RIP packet information field that counts traverses across routers. See Hop Count and Routing Interior Protocol.

HOST

The controlling computer on a network, similar to a file server on a LAN. In SNA Gateway environments, the host is usually a mainframe or minicomputer.

HOST INTERFACE ADAPTER

An add-in board for personal computers that can provide direct or remote connections to a host computer.

HOST NAME DATABASE

Contains the names, aliases (optional), and network addresses of the computers on your network.

HOST SESSION

A temporary logical connection established between two network addressable units; for example, a gateway workstation and a host computer.

HOST TABLE

A list of TCP/IP hosts on the network along with their IP addresses.

HOST2-NS

Host2 Name Server

HOSTID

The portion of the IP address that identifies the host on the IP network.

HOSTNAME

Hostname Protocol

HOT-SWAPPING

A hardware and software protocol defined by PCMCIA whereby PC cards can be removed add inserted into sockets without powering-down or rebooting the PC.

HS

National Semiconductor part prefix that indicates the device is in device family: Hybrid

HSB

See Hue/Saturation/Brightness.

HSB MODEL

See Hue/Saturation/Brightness.

HT

See Holding Timer.

HTTP

See Hypertext Transfer Protocol

HTTPS

See Hypertext Transfer Protocol Server

HTVL

Horizontal Television Lines

HUB

A wiring concentrator or multiport repeater. (Also see wiring concentrator.)

HUD

Heads Up Display

HUE

The pigment. See HSB Model.

HUE/SATURATION/ BRIGHTNESS

With the HSB model, all colors can be defined by expressing their levels of hue (the pigment), saturation (the amount of pigment) and brightness (the amount of white included), in percentages.

HYPERTEXT

See Hypertext Document

HYPERTEXT DOCUMENT

Nonsequential writing. Text that branches and allows choice to the reader, best read at an interactive screen. If you want more information on the topic, you point to the highlighted phrase and click your mouse button. You then jump to the relevant part of that document, or possibly to another document. Graphics and even sound can also be included in these files.

HYPERTEXT TRANSFER PROTOCOL

(HTTP) enables you to get hypertext files from another location. As with FTP, you run a browser program on your system that links you with a server system at another location. The local browser program sends a request to the remote server program, and, if the request is a valid one, the server returns the requested file(s).

HYPERTEXT TRANSFER PROTOCOL SERVER

(HTTPS) A program that allows a Windows NT system to become a server site on the World Wide Web.

HZ

Abbreviation for Hertz = cycles per second.