Half-Duplex Transmission — In this type of transmission, both stations may transmit and receive, but only one at a time, for example, ham radio and walkie talkies.

Handle — A handle is a value used to uniquely identify a resource so that a program can access it.

Handshaking — (1) The exchange of control codes or particular characters between two data communication systems to maintain and coordinate proper data transmission. (2) Refers to flow control in serial communication, which defines a method for the print device to tell Windows NT that its buffer is full. See also buffer.

Hard Disk Drive — See Disk Drive

Hardware Abstraction Layer (HAL) — A Windows NT service that provides basic input/output services such as timers, interrupts, and microprocessor management for computer hardware. The HAL is a device driver for the motherboard circuitry that allows the Windows NT operating system to treat different families of computers the same way.

Hardware Compatibility List (HCL) — The Windows NT Hardware Compatibility List lists the devices supported by Windows NT. The latest version of the HCL can be downloaded from the Microsoft Web Page (microsoft.com) on the Internet.

Hardware Driver — A software program which provides an interface between a specific hardware device and software programs. For example, the DOS operating system must use a mouse driver to talk to a mouse device.

Hardware tree — The hierarchical representation of all the buses and devices on a computer.

Harmonic Adapter — A simple way to convert the 50-pin Telco connection to RJ45 connections.

HBA — Host Bus Adapter. An SCSI adapter board or disk controller that functions as an interface connecting the peripheral devices to the computer.

HCL — See Hardware Compatibility List.

HCSS (High Capacity Storage System) — An NLM utility that extends the server disk capacity by integrating an optical disk library (called jukebox) into the NetWare file system.

HDLC — (High-Level Data-Link Control). A full-duplex Data-Link layer protocol that supports point-to-point connections. HDLC supports both synchronous and asynchronous transmission synchronization. Messages are transmitted in frames. It can identify error frames and selectively retransmit them.

HELP — This utility displays on-line information about using NetWare utilities.

Heterogeneous environment — An internetwork with servers and workstations running different operating systems, such as Windows NT, Macintosh, or Novell Netware, using a mix of different transport protocols.

Hexadecimal — A number system based on 16 digits (0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f — where "a" is equivalent to decimal 10 and "f" is equivalent to decimal 15). Just as 16 is an exponent of 2, the entire hexadecimal number system has an exponential relationship to binary. Therefore, hexadecimal code is an efficient means to express binary data. Where a byte in binary requires eight digits, hexadecimal only requires two digits. Binary data in the Windows Registry is expressed in hexadecimal code.

Hidden (H) Attribute — An attribute of DOS and OS/2 which prevents a directory or file from being deleted or copied. It hides the directory or file from users.

High Memory — The first 64 KB of memory located just above the 1 MB real mode boundary (1024 KB to 1088 KB) that can be used by DOS when using an extended memory manager (HIMEM.SYS) without having to change to the protected mode.

High Memory Area (HMA) — The first 64K of extended memory, into which MS-DOS 5.0, drivers and utilities can be loaded to save conventional memory. See also memory.

High Performance File System (HPFS) — An OS/2 file system that allows long file names.

HiPack — A file and folder compression format

Hive — A section of the registry that appears as a file on your hard disk. The registry subtree is divided into hives (named for their resemblance to the cellular structure of a beehive). A hive is a discrete body of keys, subkeys, and values that is rooted at the top of the registry hierarchy. A hive is backed by a single file and a .log file which are in the %SystemRoot%\system32\config or the %SystemRoot%\profiles\username folders. By default, most hive files (Default, SAM, Security, and System) are stored in the %SystemRoot%\system32\config folder. The %SystemRoot%\ profiles folder contains the user profile for each user of the computer. Because a hive is a file, it can be moved from one system to another, but can only be edited using Registry Editor.

H-node — A NetBIOS implementation that uses the p-node protocol first, then the b-node protocol if the name service is unavailable. For registration, it uses the b-node protocol, then the p-node protocol. See also p-node; NetBIOS; registration.

Home directory — A directory that is accessible to the user and contains files and programs for that user. A home directory can be assigned to an individual user or can be shared by many users.

Home page — The central document of a Web site, usually designated as the default document. The starting point for a Web site or section of a Web site is often referred to as the home page

Hop — Refers to the next router. In IP routing, packets are always forwarded one router at a time. Packets often hop from router to router before reaching their destination. See also IP address; packet; router.

Hop Count — In routing, the number of routers that must be crossed all the way from a source node to the destination node in an internetwork.

Host — (1) An internet server, often using a UNIX OS. In remote access, the term "host" could also apply to a computer providing data to the RAS client and hosting its connection to the remote network. More broadly, the term can be use for any device that is attached to the network and uses TCP/IP. See also TCP/IP. (2) Novell: The central computer or the server in a network that provides services to the clients and from which SBACKUP is run.

Host group — A set of zero or more hosts identified by a single IP destination address. See also host; IP address.

Host ID — The portion of the IP address that identifies a particular computer within a particular network ID. See also IP address; network ID.

Host name — The name of a device on a network. For a device on a Windows or Windows NT network, this can be the same as the computername, but it may not be. The host name must be in the host table or be known by a DNS server for that host to be found by another computer attempting to communicate with it. See also DNS; host table.

Host Server — The server with a backup storage device attached to it.

Host table — The HOSTS or LMHOST file that contains lists of known IP addresses mapped to host names or NetBIOS computer names. Windows uses this for local name resolution if other methods are not available

Hosts File — A file that contains the IP addresses and hostnames of the most frequently used hosts, but this file cannot contain accurate information of the whole Internet at all times.

HOSTS file — A local text file in the same format as the 4.3 Berkeley Software Distribution (BSD) UNIX \etc\hosts file. This file maps host names to IP addresses. In Windows NT, this file is stored in the \systemroot\System32\Drivers\Etc directory. See also IP address.

Hot docking — Insertion of a device in the system while the device is running at full power

Hot Fix — A method of redirecting data from any faulty block to the Hot Fix redirection area set aside on the disk to ensure that data is stored safely.

Hot Fix Area — A predefined area on the server’s disk where blocks of bad data are stored (redirected).

Hot Swapping — The process of replacing a device without bringing down the system of which it is part. For example, hot swapping a hub module occurs by sliding an active module into a fully powered up concentrator, replacing a failed module without bringing down the network.

HTML — Acronym for Hypertext Markup Language, a simple markup language used to create hypertext documents that are portable from one platform to another. HTML files are simple ASCII text files with codes embedded (indicated by markup tags) to indicate formatting and hypertext links. HTML is used for formatting documents on the World Wide Web. See Hypertext Transfer Protocol

Hub — (1) An Ethernet Data Link Layer device that connects point-to-point Physical layer links, such as twisted pair or fiber optic cables, into a single shared media network. The term hub is often used interchangeably with the term repeater. Multiport 10BASE-T, 10BASE2, and fiber optic (10BASE-FL, FOIRL) repeaters are considered hubs.
(2) A special unit in a network using a star configuration to which each workstation is connected. The hub provides a common connection so that all of the computers can communicate with one another.

Hub MIB — A specification that defines an experimental portion of the Management Information Base for use with network managing protocols in TCP/IP based internets. In particular, it defines objects for managing IEEE 802.3 10 Mbpsecond baseband repeaters (also referred to as "hubs").

Hue — The position of a color along the color spectrum. For example, green is between yellow and blue. This attribute can be set using desktop in Control Panel.

Human Interface Device (HID) specification — The device class definition developed by the USB standards group for HIDs. Serves as the basis for the WDM input device support, and unifies input devices by providing flexible data reporting, typeless data, and arrayed and variable input and output.

Hybrid topology — A combination of any two or more network topologies. Note 1: Instances can occur where two basic network topologies, when connected together, can still retain the basic network character, and therefore not be a hybrid network. For example, a tree network connected to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. Note 2: A hybrid topology always accrues when two different basic network topologies are connected.

Hyperlink — Also called simply a link. A way of jumping to another place on the Internet. Hyperlinks usually appear in a different format from regular text. You initiate the jump by clicking the link

Hypertext — Documents with links to other documents. Click a link to display the other document. A hypertext document is a document structured in chunks of text and marked up, usually using HTML, which is connected by links

Hypertext Markup Language (HTML) — A simple markup language used to create hypertext documents that are portable from one platform to another. HTML files are simple ASCII text files with codes embedded (indicated by markup tags) to indicate formatting and hypertext links. The formatting language used for documents on the World Wide Web