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half duplex (HD or HDX). Pertains to communications in which data can be sent in only one direction at a time. Contrast with duplex.

half high. Pertains to a storage device that has one half the height (41.3 mm or 1.63 inches) with the width and length the same as the full high device. See also full high.

half-session. A component that provides data flow control and transmission control at one end of a session.

halfword. A contiguous sequence of bits or characters that constitutes half a computer word and can be addressed as a unit. Contrast with word.

hand tuning. The process of modifying source code by hand to improve the performance of the resulting object code. Hand tuning is one aspect of optimization.

handle. A data structure that is a temporary local identifier for an object. You create a handle by allocating it. You make a handle identify an object at a specific location by binding it.

handler. A software routine that controls a program's reaction to specific external events, such as an interrupt handler. For Ada programming, see exception.

handshaking. The process used by modems and equipment, before transmitting data, to establish an electrical path and synchronization. See also chat script and expect-send sequence.

hard copy. A printed copy of machine output in a visually readable form such as printed reports, listings, documents, and summaries.

hard disk. See fixed disk.

hard-disk drive. See fixed-disk drive.

hard link. A mechanism that allows the ln command to assign more than one name to a file. Both the new name and the file being linked must be in the same file system.

hard return. In an Interleaf textfile, a control character created by pressing Shift-Enter that causes text to wrap to the next line.

hard space. In an Interleaf file, a nonbreaking space character.

hardware. The physical equipment of computing and computer-directed activities. The physical components of a computer system. Contrast with software.

hash codes. Format in which data is stored in compressed form.

hash signature. The fixed-length bit string resulting from hashing a character string. Character strings may be compared quickly by comparing their hash signatures.

hash table. A table of information that is accessed by way of a shortened search key (the hash value). Using a hash table minimizes average search time.

hashing. (1.) A method of transforming a search key into an address for the purpose of storing and retrieving items of data. (2.) Encoding a character string as a fixed-length bit string for comparison. The encoding may not necessarily be unique.

HCON. See 3270 Host Connection Program 2.1 and 1.3.3.

HCONMRI.3270 Host Connection Program 2.1 and 1.3.3 Message Catalog.

HCONuser. A user who has been given the special permissions necessary to use the 3270 Host Connection Program 2.1 and 1.3.3 (HCON). See also 3270 Host Connection Program 2.1 and 1.3.3.

HD. See half duplex.

HDLC. See high-level data link control.

HDR. See header label.

HDX. See half duplex.

header. (1.) Constant text that is formatted to be in the top margin of printed pages in a document. (2.) System-defined control information that precedes user data. (3.) The portion of a message that contains control information for the message such as destination fields, originating station, and priority level. (4.) In CDE, in Mailer, the basic information about an electronic mail message as it appears in the mailer container. A message header displays the name of the sender, subject, the date and time it was received, and message size.

header file. A text file that contains declarations used by a group of functions or users. Synonymous with include file.

header label (HDR). A special set of records on a diskette describing the contents of the diskette.

header page. A separator page that precedes a printed file or a print job.

header record. A record at the beginning of a file that details the sizes, locations, and other information that follows in the file.

heap. A collection of dynamically allocated variables.

HELLO. DCN Local-Network Protocol. An interior gateway protocol designed for use within autonomous systems.

'Hello, World'. The standalone sample program that introduces the fundamental construct provided by Tran-C.

help. One or more display images that describe how to use application software or how to do a system operation.

help callback. A function that calls a help.

help file. A file, separate from the source code of a program, that contains help definitions in a special help format that Base Operating System message services can use.

Help Manager. In CDE, a special help volume that lists all the online help registered on your system.

Help Viewer. In CDE, the software application that displays online help.

help volume. In CDE, a complete body of help information about a subject.

helper. A program used by the INed editor to provide extra functions for a particular type of data file.

hertz (Hz). A unit of frequency equal to one cycle per second.

heuristics. Guidelines that a system administrator uses to intervene where the two-phase commit or abort would otherwise fail.

hex. See hexadecimal.

hexadecimal (hex). Pertaining to a system of numbers to the base sixteen; hexadecimal digits range from 0 (zero) through 9 (nine) and A (ten) through F (fifteen).

hexadecimal constant. (1.) The characters 0x or 0X (zero X) followed by any digits 0 through 9 and uppercase or lowercase letters A through F. (2.) A constant, usually starting with special characters, that contains only hexadecimal digits.

HIA. See System/370 Host Interface Adapter.

hidden file. An operating system file that is not displayed by a directory listing. The name of a hidden file usually begins with a period.

hidden surface. A surface of a geometric primitive that is not visible because it is obscured by other surfaces. See also z-buffer.

hierarchical file system. In CDE, a way to organize data on computer systems using a hierarchy of containers, often called folders (directories) and files. In this scheme, folders may contain other folders and files. The successive containment of folders within folders creates the levels of organization, which is the hierarchy.

hierarchical network. A network in which hosts are administered by a tree structure of authority. This network structure relieves the administrative burden of the central authority.

hierarchy. A series of elements that have been graded or ranked in some useful manner. In AIXwindows, more than 40 classes of graphical objects are ranked top-down from the simplest to the most complex to determine the relative order of inheritance of appearance resources and behavior resources.

high-level data link control (HDLC). In data communications, the use of a specified series of bits to control data links in accordance with the International Standards for HDLC: ISO 3309 Frame Structure and ISO 4335 Elements of Procedures.

high-order. Most significant; leftmost. For example, bit 0 in a register.

higher layer or level. The conceptual level of control or processing logic existing in the hierarchical structure of a station that is above the link layer and upon which the performance of data link functions are dependent (for example, device control, buffer allocation, station management). See also level.

highlight. To emphasize an area on the display screen by any of several methods, such as brightening the area or reversing the color of characters within the area.

hiragana. A graphic character set consisting of symbols used in one of the two common Japanese phonetic alphabets. Each character is represented by 1 byte.

history. A list of Ada debugger commands entered recently. The history command has a default list of the 20 most recently entered commands. You can use history to re-enter a previous command, or to form a new command by editing the history reference text.

hit. In GL, also called pick hit or select hit. A hit occurs whenever a drawing primitive draws within the picking or selecting region. A hit is reported back to the user only if the name stack has changed since the last hit. In other words, multiple hits may occur although only one pick/select event is reported. See also picking, picking region, selecting region, and selecting.

H&J. In C.A.T terminology, the (usually automatic) process of hyphenation and justification.

hog factor. In system accounting, an analysis of how many times each command was run, how much processor time and memory it used, and how intensive that use was.

hole in a file. Empty space in a sparse file that is left open for future additions of data. See also sparse file.

Hollerith constant. In FORTRAN, a string of any characters capable of representation in the processor and preceded by nH, where n is the number of characters in the string.


home cell. See local cell.

home directory. (1.) A directory associated with an individual user. (2.) The user's current directory after login or after issuing the cd command with no argument. (3.) A parameter that supplies the full path name of the home directory for the transaction program.

home folder. In CDE, a folder where you keep personal files and additional directories. By default, File Manager and Terminal Emulator windows are set to the home folder when you first open them. When discussing command-line activities, may be called the home directory.

home session. In CDE, a choice at logout to designate a particular session, other than the one you are currently in, as the one you will automatically return to at the next login. Contrast with current session.

home-window. A window that completely displays the contents of the display buffer.

homogeneous coordinates. A four-dimensional method of representing three-dimensional space. A point (x, y, z, w) in homogeneous coordinates is used to represent a point (X, Y, Z) in three-dimensional space by taking X=x/w, Y=y/w, and Z=z/w. See also parametric bicubic surface.

hook ID. A unique number assigned to a specific trace point. All trace entries include the hook identifier of the originating trace point in the trace entry header. A hook ID is a 12-bit value. For user programs, the hook ID may be a value from 0x010 to 0x0FF. Hook identifiers are defined in the /usr/include/sys/trchkid.h file.

hooking routines. Functions that connect with the library but remain outside the library; protocol extension procedures. Synonym for stub.

hop count. In the Token-Ring Network, the number of bridges through which a frame passes on the way to its destination.

hop count metric. (1.) In a gateway, indicates that the next string represents the hop count to the destination host or network. (2.) The number of host-to-host connections in a route.

host. (1.) The primary or controlling computer in the communications network. (2.) A computer attached to a network.

host ID. An identifier for a host. A host ID uniquely identifies a host within an address family on a network but does not identify the network. A host ID is not necessarily sufficient to establish communications with a host.

host name. (1.) A name assigned to a computer connected to a network. The use of this term can be ambiguous as it can refer to either the short form name of the computer, or the fully qualified name of the computer. (2.) The Internet address of a machine in the network. Also known as host ID.

hotspot. The spot associated with a cursor that corresponds to the coordinates reported for the pointer. A cursor has an associated hotspot, which defines a point in the cursor that corresponds to the coordinates reported for the pointer.

HTML. HyperText Markup Language (HTML) is the tagging language that a web browser uses to interpret and display documents.

Huffman coding. A character-coding technique to compress data.

hyper-integer. An XDR standard that defines 64-bit (8-byte) numbers that are the extensions of integers and unsigned integers.

hyperlink. In CDE, in Help text, text or a graphic you click to display another Help topic.

hypertext. A way of presenting information online with connections between one piece of information and another. These connections are called hypertext links. Thousands of these hypertext links enable you to explore additional or related information throughout the online documentation. See also hypertext link.

hypertext link. A connection between one piece of online information and another. See also hypertext.

Hz. See hertz.

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