H

H

H n. See henry.

H.320 n. An International Telecommunications Union (ITU) standard that enables interoperability among video-conferencing equipment from different manufacturers over circuit-switched services such as ISDN, thus making desktop video conferencing viable. H.320 establishes the common formats necessary to make audio and video inputs and outputs compatible and defines a protocol that makes it possible for a multimedia terminal to use audio/visual communications links and synchronization. See also International Telecommunications Union, ISDN, video conferencing.

H.323 n. An International Telecommunications Union (ITU) interoperability protocol enabling cross-communication of multimedia products and applications over packet-based networks. Under H.323, multimedia products offered by one vendor can work with those of another, regardless of hardware compatibility. For example, a PC can share audio and video streams over either an intranet or the Internet. Applications are thus network-, platform-, and application-independent. See also International Telecommunications Union, packet switching.

H.324 n. An International Telecommunications Union (ITU) standard for simultaneously transmitting video, data, and voice over POTS (Plain Old Telephone Service) modem connections. See also POTS.

hack¹ n. 1. A modification to the code in a program, often made without taking the time to find an elegant solution. 2. A sloppy job. See also kludge (definition 2), patch¹.

hack² vb. 1. To apply creative ingenuity to a programming problem or project. 2. To alter the behavior of an application or an operating system by modifying its code rather than by running the program and selecting options.

hacker n. 1. A computerphile; a person who is totally engrossed in computer technology and computer programming or who likes to examine the code of operating systems and other programs to see how they work. 2. A person, more commonly considered a cracker, who uses computer expertise for illicit ends, such as by gaining access to computer systems without permission and tampering with programs and data. Also called: cracker. See also hacktivist.

hacktivist n. An individual who furthers political or social agendas through hacking activity. Hacktivists may break into computer systems to disrupt traffic or cause confusion, and may alter Web pages or e-mail to display content sympathetic to a specific cause. See also hacker.

HAGO n. Acronym for have a good one. An expression used to conclude e-mail messages or in signing off from IRC.

HailStorm n. See .NET My Services.

hairline n. The smallest amount of visible space or the narrowest line that is displayable on a printed page. The size of a hairline depends on the materials, hardware, and software used or on the organizations involved. The United States Postal Service defines a hairline as 1/2 point (roughly 0.007 inch), whereas the Graphic Arts Technical Foundation (GATF) defines a hairline as 0.003 inch. See also point ¹(definition 1), rule (definition 1).

HAL n. 1. See hardware abstraction layer. 2. In the 1968 book and movie 2001: A Space Odyssey by novelist Arthur C. Clarke, the intelligent but eventually psychotic computer, HAL 9000, that takes over a spaceship bound for Jupiter. The name HAL is an acronym for Heuristic/ALgorithmic computer, but the letters H-A-L are also one letter removed from I-B-M in the alphabet.

half adder n. A logic circuit that can add two input data bits and produce a sum bit and a carry bit as output. A half adder cannot accept a carry bit from a previous addition; to add two input bits and a carry bit, a full adder is required. To add two multibit binary numbers, a computer uses a half adder and one or more full adders. See also carry bit, full adder.

half-card n. See short card.

half-duplex¹ adj. Of or pertaining to two-way communication that takes place in only one direction at a time. For example, transmission between half-duplex modems occurs when one modem waits to transmit until the other has finished sending. Compare duplex¹.

half-duplex² n. Two-way electronic communication that takes place in only one direction at a time. Also called: half-duplex transmission. Compare duplex(definition 1), simplex transmission.

half-duplex transmission n. See half-duplex².

half-height drive n. Any of a generation of disk drives that are roughly one-half the height of the previous generation of drives.

half router n. A device that connects a local area network (LAN) to a communications line (such as one to the Internet) using a modem and that controls the routing of data to individual stations on the LAN.

halftone n. A printed reproduction of a photograph or other illustration, using evenly spaced spots of varying diameter to produce apparent shades of gray. The darker the shade at a particular point in the image, the larger the corresponding spot in the halftone. In traditional publishing, halftones are created by photographing an image through a screen. In desktop publishing, each halftone spot is represented by an area containing a number of dots printed by a laser printer or digital imagesetter. In both cases, the frequency of the halftone dots is measured in lines per inch. Higher printer resolution enables effective use of higher frequencies of halftone dots, enhancing image quality. See also dithering, gray scale, imagesetter, spot function.

half-word n. Half the number of bits considered to be a word in a particular computer; if a word is 32 bits, a half-word will be 16 bits or 2 bytes. See also word.

hammer n. The part of an impact printer that strikes or causes another component to strike the ribbon to print a character on the paper. In a dot-matrix printer, the pins or wires are the hammers; in a daisy-wheel printer, the hammer strikes the daisy wheel.

Hamming code n. A family of error-correction codes named for R. W. Hamming of Bell Labs. In one of the simplest Hamming codes, every 4 data bits are followed by 3 check bits, each computed from the 4 data bits. If any one of the 7 bits becomes altered, a simple computation can detect the error and determine which bit is altered. See also error-correction coding, forward error correction.

handheld computer n. A computer small enough to be held in one hand while being operated with the other hand. Handheld computers are commonly used in transportation and other field service industries. They are usually built to perform specific tasks. They often have restricted specialized keyboards rather than the standard QWERTY layout, smaller displays, input devices such as bar code readers, and communications devices for sending their data to a central computer; they rarely have disk drives. Their software is usually proprietary and stored in ROM. See also QWERTY keyboard, ROM. Compare handheld PC, PDA.

Handheld Device Markup Language n. See HDML.

Handheld Device Transport Protocol n. See HDTP.

handheld PC n. A computer that is small enough to fit in a jacket pocket and can run, for example, Windows CE (an operating system for handheld PCs and embedded systems) and applications made for that operating system. See the illustration. Acronym: HPC. Compare handheld computer, PDA.

Handheld PC.

handheld scanner n. A type of scanner used as follows: the user passes the scan head, contained within a handheld unit, over the medium being scanned, such as a piece of paper. See also scan head, scanner. Compare drum scanner, feed scanner, flatbed scanner.

handle n. 1. A pointer to a pointer; that is, a variable that contains the address of another variable, which in turn contains the address of the desired object. In certain operating systems, the handle points to a pointer stored in a fixed location in memory, whereas that pointer points to a movable block. If programs start from the handle whenever they access the block, the operating system can perform memory-management tasks such as garbage collection without affecting the programs. See also pointer. 2. Any token that a program can use to identify and access an object such as a device, a file, a window, or a dialog box. 3. One of several small squares displayed around a graphical object in a drawing program. The user can move or reshape the object by clicking on a handle and dragging. See the illustration. 4. In online communication, such as chats and bulletin boards, the name a person uses to identify himself or herself. A handle is comparable to an alias or a nickname and is like those used with CB radio. 5. A unique alphanumeric identifier of up to 10 characters assigned by InterNIC to the domain names, contacts, and network records in its domain name database. The NIC handle is used as a shorthand means of finding records and ensuring accuracy in the database. Also called: NIC handle.

Handle. A computer graphic s handle.

handler n. 1. A routine that manages a common and relatively simple condition or operation, such as error recovery or data movement. 2. In some object-oriented programming languages that support messages, a subroutine that processes a particular message for a particular class of objects. See also message, object-oriented programming.

handoff n. The process of transferring a wireless telephone signal between cell towers as a caller travels from one cell to another. A caller will not notice a smooth handoff, but an abrupt handoff can interfere with reception, with results ranging from momentary static to a disconnected call. Also called: handover. See also cell.

hands-free kit n. Wireless phone accessory that allows users to make calls without holding the phone. A basic kit includes a headset or an earpiece with a microphone. More elaborate sets for use in automobiles may include a power amplifier, dashboard microphone, phone cradle, and speakers.

handshake n. A series of signals acknowledging that communication or the transfer of information can take place between computers or other devices. A hardware handshake is an exchange of signals over specific wires (other than the data wires) in which each device indicates its readiness to send or receive data. A software handshake consists of signals transmitted over the same wires used to transfer data, as in modem-to-modem communications over telephone lines.

hands-on adj. Involving interactive work with a computer or a computer program. A hands-on tutorial, for example, would teach a skill (such as the use of a program) by means of practice sessions and question-and-answer dialogues.

handwriting input device n. A tool, such as a digital pen and tablet, used to enter text by writing instead of typing. Along with writing tablets, additional devices include 3-D drawing or computer-aided design (CAD) tablets, a tablet PC, or moving a mouse on the mouse pad.

handwriting recognition n. 1. The ability of a computer to identify a user by recognizing features of handwriting, especially a signature. 2. The ability of a computer to translate handwritten text into character data for input. This technology is still under considerable development, and most handwriting recognition programs require users to form letters and words in a very consistent and clear manner to work adequately. The development of handwriting recognition programs has been spurred by PDAs, which frequently have keyboards that are too small for data entry, and software designed for Asian markets that have languages with numerous characters, which makes keyboards a cumbersome method for entering text. See also PDA. Compare optical character recognition.

hang vb. To stop responding. A hung program or computer system does not respond to user input, but the screen looks as if everything is running normally. The program or system might be waiting for something for example, information from a network or it might have terminated abnormally. It might resume running normally on its own, or the user might need to terminate and restart the program or reboot the computer. A hung computer system is said to be locked up. See also crash² (definition 1).

hanging indent n. Placement of the beginning of the first line of a paragraph farther to the left than the subsequent lines. Also called: outdent. Compare indent.

haptics n. The study of the sense of touch. This study has extended to the study of human interaction with computer technology through tactile means. Haptics technology is central to virtual reality gaming settings, in which computers could sense and respond to finger, hand, body, or head movements. The computer could also re-create the sense of touch by altering texture, increasing resistance, or other simulations appropriate to the user s virtual reality experience. See also force feedback.

hard adj. 1. Permanent, fixed, or physically defined; unchangeable by the ordinary operation of a computer system. See also hard copy, hard error, hard return, hard-sectored disk. Compare soft (definition 1). 2. Retaining magnetization even in the absence of an external magnetic field. Compare soft (definition 2).

hard card n. A circuit board, carrying a hard disk and containing its controller, that plugs into an expansion slot and uses the expansion bus for power as well as for data and control signals. By contrast, a hard disk in a drive bay communicates with a separate controller card by a ribbon cable and has a direct cable to the computer s main power supply. See also controller, drive bay, expansion slot, ribbon cable.

hard-coded adj. 1. Designed to handle a specific situation only. 2. Depending on values embedded in the program code rather than on values that can be input and changed by the user.

hard copy n. Printed output on paper, film, or other permanent medium. Compare soft copy.

hard disk n. A device containing one or more inflexible platters coated with material in which data can be recorded magnetically, together with their read/write heads, the head-positioning mechanism, and the spindle motor in a sealed case that protects against outside contaminants. The protected environment allows the head to fly 10 to 25 millionths of an inch above the surface of a platter rotating typically at 3600 to 7200 rpm; therefore, much more data can be stored and accessed much more quickly than on a floppy disk. Most hard disks contain from two to eight platters. See the illustration. Also called: hard disk drive. Compare floppy disk.

Hard disk. The cover of this hard disk has been removed to reveal the components within.

hard disk drive n. See hard disk.

hard disk type n. One or more numbers that inform a computer about the characteristics of a hard disk, such as the number of read/write heads and the number of cylinders the hard disk contains. The hard disk type numbers are usually marked on a label attached to the disk and must be input to the computer when the hard disk is installed, often by means of the computer s CMOS setup program. See also CMOS setup.

hard error n. 1. An error caused by a hardware failure or by accessing incompatible hardware. See also hard failure. Compare soft error. 2. An error that prevents a program from returning to normal operation. See also fatal error.

hard failure n. A cessation of function from which no recovery is possible, usually requiring a call to a repair service to correct. Also called: hardware failure.

hard hyphen n. See hyphen.

hard return n. A character input by the user to indicate that the current line of text is to end and a new line is to begin. In word-processing programs that automatically break lines within the margins of a page, a hard return indicates the end of a paragraph. In text-entry programs that lack wordwrap, on the other hand, a hard return is required to end each line, and often two or more hard returns are needed to end a paragraph. See also wordwrap. Compare soft return.

hard-sectored disk n. A floppy disk whose data sectors have been physically marked with punched holes that are detected by sensors in the drive to locate the beginning of each sector. Compare soft-sectored disk.

hard space n. See nonbreaking space.

hardware n. The physical components of a computer system, including any peripheral equipment such as printers, modems, and mouse devices. Compare firmware, software.

hardware abstraction layer n. In advanced operating systems such as Windows NT, Windows 2000, and Windows XP a layer in which assembly language code is isolated. A hardware abstraction layer functions similarly to an application programming interface (API) and is used by programmers to write device-independent applications. Acronym: HAL. See also application programming interface, device independence.

hardware address n. See physical address.

hardware check n. 1. An automatic check performed by hardware to detect internal errors or problems. 2. On a PC, a check of system hardware performed by a PC s BIOS (Basic Input/Output System) during the POST (Power On Self Test) portion of the startup process.

hardware conversion n. Changing all or part of a computer system to work with new or different devices.

hardware cryptographic module n. Hardware designed to handle the cryptographic functions necessary for data security. For example, a hardware cryptographic module, or HCM, can be used in an SSL-enabled Web server to reduce CPU processing time and improve overall performance by working to secure data during online transactions. Using an HCM allows the Web server to continue processing customer requests. Acronym: HCM. See also SSL.

hardware-dependent adj. Of or pertaining to programs, languages, or computer components and devices that are tied to a particular computer system or configuration. Assembly language, for example, is hardware-dependent because it is created for and works only with a particular make or model of microprocessor.

hardware emulation layer n. In advanced operating systems such as Windows NT, Windows 2000, and Windows XP a layer in which software drivers duplicate hardware functionality. This allows software programs to use hardware features even if the hardware is not present. Acronym: HEL. Compare hardware abstraction layer.

hardware failure n. A malfunction of a physical component in a computer system, such as a disk head crash or memory error. See also hard failure.

hardware handshake n. See handshake.

hardware interrupt n. A request for service from the central processing unit, generated either externally by a hardware device such as a disk drive or an input/output port, or internally by the CPU itself. External hardware interrupts are used for such situations as a character received from a port and needing to be processed, a disk drive ready to transfer a block of data, or a tick of the system timer. Internal hardware interrupts occur when a program attempts an impossible action such as accessing an unavailable address or dividing by zero. Hardware interrupts are assigned levels of importance or priority. The highest priority is given to a type of interrupt called a nonmaskable interrupt one that indicates a serious error, such as a memory failure, that must be serviced immediately. See also external interrupt, interrupt.

hardware key n. 1. A security device connected to an input/output port to permit the use of a particular software package on that computer. The use of the hardware key permits backup copying of software but prevents its unlicensed use on additional computers. Also called: dongle. 2. Any physical device used to secure a computer system from unauthorized access, such as the lock on the front of the cabinet of some personal computers.

hardware monitor n. A separate board-level circuit used to oversee the performance of a hardware/software system. A hardware monitor can detect the cause of a fatal error such as a system crash, whereas a software monitor or debugger cannot. Compare debugger.

hardware profile n. A set of data that describes the configuration and characteristics of a given piece of computer equipment. Such data is typically used to configure computers for use with peripheral devices.

hardware tree n. In Windows 9x, a data structure containing information about the configuration and requirements of a system s hardware devices. Consisting of nodes that point to active devices, the hardware tree is dynamic and is reconstructed every time the operating system is started or refreshed. The hardware tree facilitates the Plug and Play capability of Windows 9x.

hardwired adj. 1. Built into a system using hardware such as logic circuits, rather than accomplished through programming. 2. Physically connected to a system or a network, as by means of a network connector board and cable.

Harvard architecture n. A processor architecture that uses separate address buses for code and for data. This increases throughput by allowing the system to fetch instructions at the same time that it reads and writes data. This architecture also allows optimization of memory system design because instructions tend to be fetched sequentially, whereas data reads and writes are more random.

Harvard Mark I n. See Mark I.

Harvest research project n. See ICP.

hash¹ n. In many FTP client programs, a command that instructs the FTP client to display a pound sign (#) each time it sends or receives a block of data. See also FTP client.

hash² vb. To be mapped to a numerical value by a transformation known as a hashing function. Hashing is used to convert an identifier or key, meaningful to a user, into a value for the location of the corresponding data in a structure, such as a table. For example, given the key MOUSE and a hashing function that added up the ASCII values of the characters, divided the total by 127, and took the remainder, MOUSE would hash to 12 and the data identified by MOUSE would be found among the items in entry 12 in the table.

hash coding n. See hash².

hashing algorithm n. A formula used to generate hash values and digital signatures. Also called: hash function.

hash search n. A search algorithm that uses hashing to find an element of a list. Hash searches are highly efficient because the hashing enables direct or almost direct access to the target element. See also binary search, hash, linear search, search algorithm.

hash total n. An error-checking value derived from the addition of a set of numbers taken from data (not necessarily numeric data) that is to be processed or manipulated in some way. After processing, the hash total is recalculated and compared with the original total. If the two do not match, the original data has been changed in some way.

hash value n. A value used in creating digital signatures. This value is generated by imposing a hashing algorithm onto a message. This value is then transformed, or signed, by a private key to produce a digital signature. Also called: message digest.

Haskell n. A functional programming language based on lambda calculus and suitable for the creation of applications that need to be highly modifiable.

Hayes-compatible adj. Responding to the same set of commands as the modems manufactured by Hayes Microcomputer Products. This command set has become the de facto standard for microcomputer modems.

HCM n. See hardware cryptographic module.

HDBMS n. See hierarchical database management system.

HDCP n. Acronym for High-bandwidth Digital Content Protection. An encryption and authentication specification created by Intel for Digital Video Interface (DVI) devices such as digital cameras, high-definition televisions, and video disk players. HDCP is designed to protect transmissions between DVI devices from being copied.

HDF n. See Hierarchical Data Format.

HDLC n. Acronym for High-level Data Link Control. A protocol for information transfer adopted by the ISO. HDLC is a bit-oriented, synchronous protocol that applies to the data-link (message-packaging) layer (layer 2 of the ISO/OSI reference model) for computer-to-microcomputer communications. Messages are transmitted in units called frames, which can contain differing amounts of data but which must be organized in a particular way. See also frame (definition 1), ISO/OSI reference model.

HDML n. Acronym for Handheld Device Markup Language. A simple, first-generation markup language used to define hypertext-like content and applications for wireless and other handheld devices with small displays. This language is used primarily to create Web sites viewed via wireless phones and personal digital assistants (PDAs). HDML provides content consisting mainly of text with limited graphics. See also WML.

HDSL n. Acronym for High-bit-rate Digital Subscriber Line. A form of DSL, HDSL is a protocol for digital transmission of data over standard copper telecommunications lines (as opposed to fiber-optic lines) at rates of 1.544 Mbps in both directions. Also called: High-data-rate Digital Subscriber Line. See also DSL.

HDTP n. Acronym for Handheld Device Transport Protocol. Protocol that enables a handheld device, such as a wireless phone or personal digital assistant (PDA), to access the Internet. HDTP regulates the input and output of data interpreted by the device s microbrowser. See also WAP.

HDTV n. Acronym for High-Definition TeleVision. A new television display standard that doubles the existing screen resolution and increases the screen aspect ratio from 4:3 to 16:9. This aspect ratio creates a television screen that is shaped like a movie screen.

HDTV-over-IP n. An Internet-based delivery option for High Definition Television (HDTV). HDTV-over-IP provides options for new and expanded services to ISPs, cable companies, telecommunications carriers, and business intranets, with its most extensive use in education. Universities use high-speed networks such as Internet2 to provide the intensive bandwidth demanded by HDTV-over-IP. Because HDTV-over-IP offers extreme image fidelity and sharpness, it is seen as ideal for delivery of distance education courses requiring precise visuals for which conventional video cannot provide sufficient resolution. Also called: iHDTV.

head n. 1. The read/write mechanism in a disk or tape drive. It converts changes in the magnetic field of the material on the disk or tape surface to changing electrical signals and vice versa. Disk drives usually contain one head for each surface that can be read from and written to. 2. In relation to software or documents, the top or beginning of something. 3. In HTML, a section of coding that precedes the body of a document and is used to describe the document itself (title, author, and so on) rather than the elements within the document.

head arm n. See access arm.

head-cleaning device n. An apparatus for applying a small amount of cleaning fluid to a magnetic head to remove accumulated debris.

head crash n. A hard disk failure in which a read/write head, normally supported on a cushion of air only millionths of an inch thick, comes into contact with the platter, damaging the magnetic coating in which data is recorded. Still more damage occurs when the head picks up material gouged out of the surface and pushes it. A head crash can be caused by mechanical failure or by heavy shaking of the disk drive. If the crash occurs on a directory track, the whole disk may become instantly unreadable.

header n. 1. In word processing or printing, text that is to appear at the top of pages. A header might be specified for the first page, all pages after the first, even pages, or odd pages. It usually includes the page number and may also show the date, the title, or other information about a document. Also called: heading, running head. Compare footer. 2. An information structure that precedes and identifies the information that follows, such as a block of bytes in communications, a file on a disk, a set of records in a database, or an executable program. 3. One or more lines in a program that identify and describe for human readers the program, function, or procedure that follows.

header file n. A file that is identified to be included at the beginning of a program in a language such as C and that contains the definitions of data types and declarations of variables used by the functions in the program.

header label n. An initial structure, such as an opening record, in the linear organization of a file or communication that describes the length, type, and structure of the data that follows. Compare trailer label (definition 1).

header record n. The first record in a sequence of records.

heading n. See header (definition 1).

headless computer n. A computer system that does not have a keyboard, mouse, or video monitor during normal operation.

head-mounted device n. A headset or helmet used with virtual reality systems ranging from gaming to military, medical, educational, and industrial applications. A head-mounted device contains small screens that display images in such a way that the headset allows the wearer to view and move about in a three-dimensional, virtual world. The simulated environment is generated by a controlling computer, which adjusts the images in accordance with the wearer s head and body movements. A head-mounted device can include audio capability and is often used with an interactive input device, such as a joystick or glove. Acronym: HMD. See also virtual reality, wearable computer.

head-per-track disk drive n. A disk drive that has one read/write head for every data track. Such a disk drive has a very low seek time because the heads do not have to move across the disk surface to the required track for reading and writing. Because read/write heads are expensive, this type of drive is uncommon.

head positioning n. The process of moving the read/write head of a disk drive to the proper track for reading and writing.

head slot n. The oblong opening in the jacket of a floppy disk that provides access to the magnetic surface of the disk for the read/write head. See the illustration.

Head slot.

head switching n. The process of electrically switching among multiple read/write heads in a disk drive.

heap n. 1. A portion of memory reserved for a program to use for the temporary storage of data structures whose existence or size cannot be determined until the program is running. To build and use such elements, programming languages such as C and Pascal include functions and procedures for requesting free memory from the heap, accessing it, and freeing it when it is no longer needed. In contrast to stack memory, heap memory blocks are not freed in reverse of the order in which they were allocated, so free blocks may be interspersed with blocks that are in use. As the program continues running, the blocks may have to be moved around so that small free blocks can be merged together into larger ones to meet the program s needs. See also garbage collection. Compare stack. 2. A complete binary tree in which the value of any node is not exceeded by the value of either of its children. See also binary tree.

heap sort or heapsort n. A space-efficient sorting method that first arranges the key fields into a heap structure; then repeatedly removes the root of the heap, which must, by definition, have the largest key; and re-forms the heap. See also heap (definition 1).

heat pipe n. A cooling device consisting of a sealed metal tube containing a liquid and a wick. The liquid evaporates at the hot end; the vapor spreads along the tube to the cold end, where it condenses onto the wick; the liquid flows back along the wick to the hot end by capillary action. Heat pipes have been used in Pentium-based laptop computers, which have high cooling requirements and little room for conventional heat sinks. Compare heat sink.

heat sink n. A device that absorbs and dissipates heat produced by an electrical component, such as an integrated circuit, to prevent overheating. Heat sinks are usually made of metal and often have fins that assist in transferring heat to the atmosphere. See the illustration. Compare heat pipe.

Heat sink.

hecto- prefix Metric prefix meaning 10² (one hundred).

HEL n. See hardware emulation layer.

hello, world n. The output of the first program in Brian Kernighan and Dennis Ritchie s The C Programming Language. The program is traditionally the first test a C programmer makes in a new environment.

help n. 1. The capability of many programs and operating systems to display advice or instructions for using their features when so requested by the user, as by a screen button or a menu item or a function key. The user can access help without interrupting work in progress or leafing through a manual. Some help facilities are context-sensitive, meaning that the user receives information specific to the task or command being attempted. Also called: online help. 2. In many applications, a command that displays an explanation of another command that follows it. For instance, in many FTP programs, the command help can be followed by other commands, such as cd (change directory) or ls (list files and directories), to discover the purpose of these other commands. 3. In versions 5 and 6 of MS-DOS, the command used to request information about MS-DOS commands, command parameters, and switches.

Help n. An item on a menu bar in a graphical user interface that enables the user to access the help feature of the present application. See also graphical user interface, help (definition 1), menu bar.

help desk n. 1. Technical support staff who help solve users problems with hardware or software systems or refer such problems to those who can solve them. Help desks are typically run by larger organizations, such as corporations, universities, or vendors to corporations, to assist users in the organization. 2. A software application for tracking problems with hardware and software and their solutions.

helper n. See helper application.

helper application n. An application intended to be launched by a Web browser when the browser downloads a file that it is not able to process itself. Examples of helper applications are sound and movie players. Helper applications generally must be obtained and installed by users; they usually are not included in the browser itself. Many current Web browsers no longer require helper applications for common multimedia file formats. Also called: helper program. Compare ActiveX controls, plug-in (definition 2).

helper program n. See helper application.

Help key n. A key on the keyboard that the user can press to request help. See also function key, help (definition 1).

help screen n. A screen of information that is displayed when the user requests help. See also help (definition 1).

henry n. The unit of inductance. A current changing at a rate of one ampere per second will generate one volt across an inductance of one henry. In practice, a henry is a very large unit; inductances measured in millihenries (mH = 10 ³ H), microhenries (<MU>H = 10 ⁶ H), or nanohenries (nH = 10 ⁹ H) are more commonly encountered. Abbreviated H. See also inductance.

Hercules Graphics Card n. See HGC.

hertz n. The unit of frequency measurement; one cycle (of a periodic event such as a waveform) per second. Frequencies of interest in computers and electronic devices are often measured in kilohertz (kHz = 1000 Hz = 10³ Hz), megahertz (MHz = 1000 kHz = 10⁶ Hz), gigahertz (GHz = 1000 MHz = 10⁹ Hz), or terahertz (THz = 1000 GHz = 10¹² Hz). Abbreviated Hz.

hertz time n. See clock rate.

heterogeneous environment n. A computing milieu, usually within an organization, in which hardware and software from two or more manufacturers are used. Compare homogeneous environment.

heuristic n. An approach or algorithm that leads to a correct solution of a programming task by nonrigorous or self-learning means. One approach to programming is first to develop a heuristic and then to improve on it. The term comes from Greek heuriskein ( to discover, find out ) and is related to eureka ( I have found it ).

Hewlett-Packard Graphics Language n. See HPGL.

Hewlett-Packard Printer Control Language n. See Printer Control Language.

hex n. See hexadecimal.

hexadecimal adj. Using 16 rather than 10 as the base for representing numbers. The hexadecimal system uses the digits 0 through 9 and the letters A through F (uppercase or lowercase) to represent the decimal numbers 0 through 15. One hexadecimal digit is equivalent to 4 bits, and 1 byte can be expressed by two hexadecimal digits. For example, binary 0101 0011 corresponds to hexadecimal 53. To prevent confusion with decimal numbers, hexadecimal numbers in programs or documentation are usually followed by H or preceded by &, $, or 0x. Thus, 10H = decimal 16; 100H = decimal 16² = decimal 256. Equivalents and conversion tables for binary, decimal, hexadecimal, and octal numbers are given in Appendix E. Also called: hex.

hexadecimal conversion n. Conversion of a number to or from the hexadecimal system. See Appendix E.

HFS n. See Hierarchical File System.

HFS+ n. Acronym for Hierarchal File System Plus. The primary file system format available on the Macintosh operating system. With Mac OS 8.1, HFS+ replaced the earlier HFS format, adding support for names longer than 31 characters and Unicode representation of file and directory names. Also called: Mac OS Extended format.

HGA n. Acronym for Hercules Graphics Adapter. See HGC.

HGC n. Acronym for Hercules Graphics Card. A video adapter introduced in 1982 by Hercules Computer Technology for IBM personal computers and compatibles and now superseded by VGA and its successors. It offered a monochrome graphics mode with 720 x 348 pixels. See also VGA.

HGC Plus n. A video adapter, introduced in 1986 by Hercules Computer Technology, that offered additional video buffer space to store 12 fonts of 256 characters each, which could be used for graphics characters.

HHOK n. Acronym for ha, ha, only kidding. An indication of humor or facetiousness often used in e-mail and online communications.

hibernation n. A state in which a computer shuts down after saving everything in memory to the hard disk. When the computer is powered on, programs and documents that were open are restored to the desktop. See also standby.

hidden file n. A file that, in order to protect it from deletion or modification, is not shown in the normal listing of the files contained in a directory. Such a file is often used to store code or data critical to the operating system.

hidden line n. In any application, such as a CAD program, that represents solid three-dimensional objects, a line in a drawing that would (or should) be hidden if the object were perceived as a solid construction. The process of removing such lines in an application is called hidden-line removal. See also CAD, hidden surface.

hidden surface n. A surface of a solid three-dimensional object, such as one represented in a CAD program, that would not be visible when the object is viewed from a particular angle for example, the underside of the wing of an airplane when viewed from above. See also CAD, hidden line.

hide vb. To temporarily remove the onscreen display of an application s active window while leaving the application running. Windows that have been hidden are returned to active display by issuing the appropriate command to the operating system.

hierarchical adj. Of, relating to, or organized as a hierarchy. See also hierarchy.

hierarchical computer network n. 1. A network in which one host computer controls a number of smaller computers, which may in turn act as hosts to a group of PC workstations. 2. A network in which control functions are organized according to a hierarchy and in which data processing tasks may be distributed.

hierarchical database n. A database in which records are grouped in such a way that their relationships form a branching, treelike structure. This type of database structure, most commonly used with databases for large computers, is well suited for organizing information that breaks down logically into successively greater levels of detail. The organization of records in a hierarchical database should reflect the most common or the most time-critical types of access expected.

hierarchical database management system n. A database management system that supports a hierarchical model. Acronym: HDBMS. See also hierarchical model.

Hierarchical Data Format n. A file format for storing multiple types of graphical and numerical data and transferring them between different types of machines, together with a library of functions for handling such files in a uniform way. NCSA developed and supports the file function and library and has placed them in the public domain. Hierarchical Data Format files are supported on most common types of computers. The format can easily be extended to accommodate additional data models. The library functions have both FORTRAN and C interfaces. Acronym: HDF. See also NCSA (definition 1).

hierarchical file system n. A system for organizing files on a disk in which files are contained in directories or folders, each of which can contain other directories as well as files. The main directory for the disk is called the root; the chain of directories from the root to a particular file is called the path. See also hierarchy, path (definition 2), root. Compare flat file system.

Hierarchical File System n. A tree-structured file system used on the Apple Macintosh in which folders can be nested within other folders. Acronym: HFS. See also hierarchy, path (definition 2), root. Compare flat file system.

hierarchical menu n. A menu that has one or more submenus. Such a menu/submenu arrangement is hierarchical because each level subsumes the next.

hierarchical model n. A model used in database management in which each record may be the parent of one or more child records, which may or may not have the same structure as the parent; a record can have no more than one parent. Conceptually, therefore, a hierarchical model can be, and usually is, regarded as a tree. The individual records are not necessarily contained in the same file. See also tree.

Hierarchical Storage Management n. See HSM.

hierarchy n. A type of organization that, like a tree, branches into more specific units, each of which is owned by the higher-level unit immediately above. Hierarchies are characteristic of several aspects of computing because they provide organizational frameworks that can reflect logical links, or relationships, between separate records, files, or pieces of equipment. For example, hierarchies are used in organizing related files on a disk, related records in a database, and related (interconnected) devices on a network. In applications such as spreadsheets, hierarchies of a sort are used to establish the order of precedence in which arithmetic operations are to be performed by the computer. See also hierarchical file system.

high availability n. The ability of a system or device to be usable when it is needed. When expressed as a percentage, high availability is the actual service time divided by the required service time. Although high availability does not guarantee that a system will have no downtime, a network often is considered highly available if it achieves 99.999 percent network uptime. Also called: RAS (reliability/availability/serviceability), fault resilience. See also five-nines availability, four-nines availability, three-nines availability, two-nines availability. Compare fault tolerance.

High-bit-rate Digital Subscriber Line n. See HDSL.

high byte n. The byte containing the most significant bits (bits 8 through 15) in a 2-byte grouping representing a 16-bit (bits 0 through 15) value. See the illustration. See also hexadecimal.

High byte. The high byte is binary 01101100 or hexadecimal 6C or decimal 108.

high-capacity CD-ROM n. See digital video disc.

High Contrast n. An accessibility display feature in Microsoft Windows that instructs programs to use the color scheme specified in the Settings dialog box and to increase legibility whenever possible.

High-data-rate Digital Subscriber Line n. See HDSL.

High-Definition Television n. See HDTV.

high-density disk n. 1. A 3.5-inch floppy disk that can hold 1.44 MB. Compare double-density disk. 2. A 5.25-inch floppy disk that can hold 1.2 MB. Compare double-density disk.

high DOS memory n. See high memory.

high-end adj. A descriptive term for something that uses the latest technology to maximize performance. There is usually a direct correlation between high-end technology and higher prices.

High-level Data Link Control n. See HDLC.

high-level language n. A computer language that provides a level of abstraction from the underlying machine language. Statements in a high-level language generally use keywords similar to English and translate into more than one machine-language instruction. In practice, every computer language above assembly language is a high-level language. Acronym: HLL. Also called: high-order language. Compare assembly language.

highlight vb. To alter the appearance of displayed characters as a means of calling attention to them, as by displaying them in reverse video (light on dark rather than dark on light, and vice versa) or with greater intensity. Highlighting is used to indicate an item, such as an option on a menu or text in a word processor, that is to be acted on in some way.

high memory n. 1. Memory locations addressed by the largest numbers. 2. In IBM PCs and compatibles, the range of addresses between 640 kilobytes and 1 megabyte, used primarily for the ROM BIOS and control hardware such as the video adapter and input/output ports. Compare low memory.

high memory area n. In IBM PCs and compatibles, the 64-kilobyte range of addresses immediately above 1 megabyte. By means of the file HIMEM.SYS, MS-DOS (versions 5 and later) can move portions of itself into the high memory area, thereby increasing the amount of conventional memory available for applications. Acronym: HMA. See also conventional memory, expanded memory.

high-order adj. Having the most weight or significance. The high-order term usually appears first or leftmost in writing systems based on the Roman alphabet or Arabic numerals. For example, in the 2-byte hex value 6CA2, the high-order byte 6C has a value by itself of decimal 108 but counts for 108 x 256 = 27,648 in the group, whereas the low-order byte A2 counts only for decimal 162. Compare low-order.

high-order language n. See high-level language.

highpass filter n. An electronic circuit that passes all frequencies in a signal that are above a specified frequency. Compare bandpass filter, lowpass filter.

High-Performance File System n. See HPFS.

High-Performance Parallel Interface n. See HIPPI.

High-Performance Serial Bus n. See IEEE 1394.

high-persistence phosphor n. A phosphor that glows for a relatively long time after being struck by electrons. High-persistence phosphors are used in direct view storage tubes, but most CRTs (cathode-ray tubes) use phosphors of relatively low persistence so that their images can be changed quickly without ghosts of earlier images remaining on the screen. See also CRT, direct view storage tube.

high resolution n. The capability for reproducing text and graphics with relative clarity and fineness of detail. High resolution is achieved by using a large number of pixels (dots) to create an image in a given area. For screen displays, the resolution is stated in terms of the total number of pixels in the horizontal and vertical dimensions. For example, the VGA video adapter has a resolution of 640 by 480 pixels. In printing, resolution refers to the number of dots per inch (dpi) produced by the printer, such as 300 to 600 dpi for a desktop laser or ink-jet printer or 1000 to 2000 dpi for a production-quality imagesetter. Also called: hi-res.

High Sierra specification n. An industry-wide format specification for the logical structure, file structure, and record structures on a CD-ROM. The specification is named after a meeting on CD-ROM held near Lake Tahoe in November 1985. It served as the basis for the international standard, ISO 9660.

high tech n. 1. Cutting-edge applied science and engineering, usually involving computers and electronics. 2. Sophisticated, often complex, specialized technical innovation.

hijackware n. Software that appears to be a useful plug-in or utility, but which will take over a user s Internet surfing or shopping activity by creating pop-up advertisements for competing products or redirecting the user to competitor s Web sites. Typically users will download and install a hijackware product believing it to be free browser enhancement software. Businesses pay the makers of hijackware products to push their shopping sites and product advertising onto Internet users, sometimes to the point of denying the user access to competing Web sites. See also gatored.

Hijiri calendar n. The lunar calendar used in Islamic countries. See Julian calendar. Compare Gregorian calendar.

HIPPI n. Acronym for High-Performance Parallel Interface. An ANSI communications standard used with supercomputers.

hi-res n. See high resolution.

histogram n. A chart consisting of horizontal or vertical bars, the widths or heights of which represent the values of certain data.

history n. A list of the user s actions within a program, such as commands entered in an operating system shell, menus passed through using Gopher, or links followed using a Web browser.

hit n. 1. A successful retrieval of data from a cache rather than from the slower hard disk or RAM. See also cache, hard disk, RAM. 2. A successful retrieval of a record matching a query in a database. See also query (definition 1), record. 3. Retrieval of a file from a Web site. Each separate file accessed on a Web page, including HTML documents and graphics, counts as a hit. 4. In computer war and other games, when a character is successfully fired on, attacked, or otherwise taken out.

hit points n. Used in most computer and console war games to refer to the amount of times a player can be damaged before his or her character passes out or dies.

hive n. One of the top-level sets of keys, subkeys, and values in Windows 9x, Windows NT, Windows 2000, and Windows CE Registries. The term was created by a Microsoft programmer who thought the structure of the Registry resembled a beehive. Each hive is a permanent part of the Registry and is associated with a set of files containing information related to the configuration (applications, user preferences, devices, and so on) of the computer on which the operating system is installed. Registry hives include HKEY_LOCAL_MACHINE, HKEY_CURRENT_USER, and HKEY_CURRENT_CONFIG. See also Registry.

HKEY n. Short for hkey handle. In Windows 9x, Windows NT, and Windows 2000, a handle to a Registry key in which configuration information is stored. Each key leads to subkeys containing configuration information that, in earlier versions of Windows, was stored in .ini files. For example, the handle key HKEY_CURRENT_USERControl Panel leads to the subkey for the Windows Desktop. See also handle (definition 1).

HLL n. See high-level language.

HLS n. Acronym for hue-lightness-saturation. See HSB.

HMA n. See high memory area.

HMD n. See head-mounted device.

Hollerith tabulating/recording machine n. An electromechanical machine invented by Herman Hollerith in the late 1800s for processing data supplied in the form of holes punched at predetermined locations in cards. Contacts made through the holes completed electrical circuits, allowing signals to be passed to counting and tabulating devices. This machine is considered to have reduced the time required to finish the 1890 U.S. census by two-thirds. Such machines were manufactured in the early 1900s by Hollerith s Tabulating Machine Company, which eventually became the International Business Machines Corporation (IBM).

hologram n. A three-dimensional image record created by holography. The hologram consists of a light interference pattern preserved in a medium such as photographic film. When suitably illuminated, it produces an image that changes its appearance as the viewer changes viewing angle. See also holography.

holography n. A method of reproducing three-dimensional visual images by recording light interference patterns on a medium such as photographic film, creating a hologram. See also hologram.

holy war n. 1. A widespread and acrimonious debate among computer professionals over some aspect of the computer field, such as the debate over use of the GOTO statement in programming or that over big-endian versus little-endian data storage. 2. An argument in a mailing list, newsgroup, or other forum over some emotional and controversial topic, such as abortion or Northern Ireland. Introducing a holy war that is off the purported topic of the forum is considered a violation of netiquette.

home n. A beginning position, such as the upper left corner of a character-based display, the left end of a line of text, cell A1 of a spreadsheet, or the top of a document.

home automation n. The process of programmatically controlling appliances, lighting, heating and cooling systems, and other devices in a home network. See also home network (definition 1).

homebrew n. Hardware or software developed by an individual at home or by a company for its own use rather than as a commercial product, such as hardware developed by electronics hobbyists when microcomputers first appeared in the 1970s.

home computer n. A personal computer designed and priced for use in the home.

home controller n. A software or hardware interface used to control the systems in a home network for home automation.

home directory n. A directory associated with a user account under UNIX. The home directory is the current directory when the user first logs in, and the user can return to it by entering the command cd (change directory) without a pathname. The user s files will ordinarily be stored in the home directory and its descendants.

homegrown software n. Software developed by an individual at home rather than in a professional environment. Most public-domain and shareware programs are created this way.

Home key n. A key, found on most keyboards, whose function usually involves sending the cursor to some type of home position in an application. See also home.

home network n. 1. A communications network in a home or building used for home automation. Home networks can use wiring (existing or new) or wireless connections. See also home automation, home controller. 2. Two or more computers in a home that are interconnected to form a local area network (LAN).

home office n. 1. An office set up within a residence. 2. The main headquarters of a company.

home page n. 1. A document intended to serve as a starting point in a hypertext system, especially the World Wide Web. A home page is called a start page in Microsoft Internet Explorer. 2. An entry page for a set of Web pages and other files in a Web site. 3. A personal Web page, usually for an individual.

Home Phoneline Networking Alliance n. See HomePNA.

HomePNA n. Short for Home Phoneline Networking Alliance. An association of more than 100 companies working toward the adoption of a unified technology for setting up home networks over existing telephone wiring. Phoneline networking allows multiple PCs, printers, and peripheral devices to be connected for such purposes as multiplayer gaming, sharing printers and other peripherals, and rapid downloads over the Internet. The alliance was founded by a number of companies including IBM, Intel, AT&T, and Lucent Technologies.

Home Radio Frequency n. See HomeRF.

home record n. See header record.

HomeRF n. Acronym for Home Radio Frequency. A wireless home-networking specification that uses the 2.4-GHz frequency band to communicate between computers, peripherals, cordless phones, and other devices. HomeRF is supported by Siemens, Compaq, Motorola, National Semiconductor, Proxim, and other companies.

homogeneous environment n. A computing milieu, usually within an organization, in which only one manufacturer s hardware and one manufacturer s software are used. Compare heterogeneous environment.

homogeneous network n. A network on which all the hosts are similar and only one protocol is used.

Honeynet Project n. A nonprofit security research group created to collect and analyze data on hacking tools and methods by maintaining a decoy network of computers that is potentially attractive to hackers. The Honeynet Project sets up entire networks of computers in different combinations of operating systems and security to realistically simulate those used in businesses and organizations. Hackers are lured to the network where all inbound and outbound data is captured and contained to help researchers learn about hacker tactics and motives.

honeypot n. A security program designed to lure and distract a network attacker with decoy data. The honeypot appears to be a system that the intruder would like to crack but which, in reality, is safely separated from the actual network. This allows network administrators to observe attackers and study their activities without the intruders knowing they are being monitored. Honeypot programs get their name from the like a bear to honey metaphor.

honker n. A slang term for a hacker, the term originated in China. The Honker Union of China is an active group of Chinese hackers with nationalistic or hacktivist aims. The Honker Union of China has claimed patriotic motivation for defacing Japanese and U.S. Web sites, hacking U.S. networks, and releasing the Lion worm and other malicious programs. See also hacktivist, Lion worm.

hook n. A location in a routine or program in which the programmer can connect or insert other routines for the purpose of debugging or enhancing functionality.

hop n. In data communications, one segment of the path between routers on a geographically dispersed network. A hop is comparable to one leg of a journey that includes intervening stops between the starting point and the destination. The distance between each of those stops (routers) would be a communications hop.

horizontal blanking interval n. See blanking, horizontal retrace.

horizontal flyback n. See horizontal retrace.

horizontal market n. A broad category of business activity, such as accounting or inventory control, that carries across many types of business. Compare vertical market.

horizontal market software n. Application programs, such as word processors, that can be used in all types of business, as opposed to those geared for a certain industry.

horizontal retrace n. The movement of the electron beam in a raster-scan video display from the right end of one scan line to the left end (the beginning) of the next. During horizontal retrace, the electron beam is turned off, so the time required for the beam to move is called the horizontal blanking interval. See also blanking. Compare vertical retrace.

horizontal scrolling n. A feature of programs such as word processors and spreadsheets that enables the user to scroll left and right to display information beyond the horizontal limits of the screen (or window, in a graphical user interface).

horizontal synchronization n. On raster displays, the timing produced by a signal that controls the sweep of the display s electron beam as it moves from left to right and back again to form an image line by line. The horizontal synchronization signal is usually controlled by a circuit known as a phase-locked loop, which maintains a constant precise frequency so that a clear image is formed.

host¹ n. 1. The main computer in a mainframe or minicomputer environment that is, the computer to which terminals are connected. 2. In PC-based networks, a computer that provides access to other computers. 3. On the Internet or other large networks, a server computer that has access to other computers on the network. A host computer provides services, such as news, mail, or data, to computers that connect to it.

host² vb. To provide services to client computers that connect from remote locations for example, to offer Internet access or to be the source for a news or mail service.

host adapter n. A device for connecting a peripheral to the main computer, typically in the form of an expansion card. Also called: controller, host bus adapter.

hosting n. The practice of providing computer and communication facilities to businesses or individuals, especially for use in creating Web and electronic commerce sites. A hosting service can provide high-speed access to the Internet, redundant power and data storage, and 24-hour maintenance at lower cost than implementing the same services independently. See also host, virtual hosting.

Host Integration Server n. A software application from Microsoft Corporation to allow businesses to integrate existing application, data, and network assets with new business applications and technologies. Host Integration Server preserves a company s existing legacy infrastructure and investments, while providing out-of-the-box development tools that enable integration with client/server and Web networks.

host language n. 1. The machine language of a CPU. 2. A high-level language that is specifically supported by an operating system with its toolbox routines and native development systems.

host name n. The name of a specific server on a specific network within the Internet, leftmost in the complete host specification. For example, www.microsoft.com indicates the server called www within the network at Microsoft Corporation.

host not responding n. An error message issued by an Internet client indicating that the computer to which a request has been sent is refusing the connection or is otherwise unavailable to respond to the request.

host replacement n. See rehosting.

host timed out n. An error condition that occurs when a remote system fails to respond within a reasonable amount of time (a few minutes) during an exchange of data over a TCP connection. This condition may mean that the remote system has crashed or been disconnected from the network. The error message the user sees may or may not be phrased in this manner. See also TCP. Compare host not responding.

host unreachable n. An error condition that occurs when the particular computer to which the user wishes to connect over a TCP/IP network cannot be accessed on its LAN because it is either down or disconnected from the network. The error message the user sees may or may not be phrased in this manner. See also TCP/IP.

hot adj. Of special or urgent interest, or deemed popular.

HotBot n. An Internet search engine developed by Inktomi Corporation and HotWired, Inc. Using Slurp, a Web robot, this tool maintains a database of documents that can be matched to key words entered by the user, in a fashion similar to other search engines. HotBot incorporates many workstations in parallel to search and index Web pages. See also spider.

hot carrier diode n. See Schottky diode.

hot docking n. The process of attaching a laptop computer to a docking station while the computer is running, and automatically activating the docking station s video display and other functions. See also docking station, laptop.

hot insertion n. The insertion of a device or card while there is power to the system. Many newer laptops allow for hot insertion of PCMCIA cards. High-end servers may also allow hot insertion to reduce downtimes.

HotJava n. A Web browser developed by Sun Microsystems, Inc., that is optimized to run Java applications and applets embedded in Web pages. See also applet, Java, Java applet.

hot key¹ n. A keystroke or combination of keystrokes that switches the user to a different program, often a terminate-and-stay-resident (TSR) program or the operating system user interface. See also TSR.

hot key² vb. To transfer to a different program by pressing a hot key.

hot link n. A connection between two programs that instructs the second program to make changes to data when changes occur in the first program. For example, a word processor or desktop publishing program could update a document based on information obtained from a database through a hot link. See hyperlink.

hotlist n. A list of frequently accessed items, such as Web pages in a Web browser, from which the user can select one. The hotlist of Web pages is called the bookmark list in Netscape Navigator and Lynx and is called the Favorites folder in Microsoft Internet Explorer.

Hotmail n. A Web-based e-mail service launched in 1996 and owned and operated by Microsoft since December 1997. Hotmail provides free e-mail accounts and can be used by anyone with Internet access and Web browsing software.

hot plugging n. A feature that allows equipment to be connected to an active device, such as a computer, while the device is powered on.

hot-potato routing n. A packet routing scheme that relies on keeping data moving, even if it may temporarily move away from its final destination. Also called: deflection routing.

hot spare n. In RAID (redundant array of independent disks) systems, a spare drive in the array that is configured as a backup on which data can be rebuilt in the event that another drive fails. Hot spares are kept on line and do not require operator intervention to be activated. See also RAID.

hot spot n. The position in a mouse pointer, such as the position at the tip of an arrow or the intersection of the lines in a cross, that marks the exact location that will be affected by a mouse action, such as a button press.

hot swapping n. See hot plugging.

HotSync n. Software application from Palm that permits data synchronization between a Palm handheld computing device and another computing device, such as a laptop or personal computer. The synchronization occurs via a cable connection or wirelessly (for example, via infrared signals).

HotWired n. A Web site affiliated with Wired magazine that contains news, gossip, and other information about the culture of the Internet.

housekeeping n. Any of various routines, such as updating the clock or performing garbage collection, designed to keep the system, the environment within which a program runs, or the data structures within a program in good working order.

hover button n. Text or an image on a Web page, usually in the form of a button, that changes appearance when a cursor passes over it. The hover button may change color, blink, display a pop-up with additional information, or produce other similar effects. Hover buttons are usually implemented through ActiveX objects and scripting, although hover behavior can also be set through HTML attributes.

HPC n. See handheld PC.

HPFS n. Acronym for High Performance File System. A file system available with OS/2 versions 1.2 and later. See also FAT file system, NTFS.

HPGL n. Acronym for Hewlett-Packard Graphics Language. A language originally developed for images destined for plotters. An HPGL file consists of instructions that a program can use to reconstruct a graphical image.

HPIB n. Acronym for Hewlett-Packard Interface Bus. See general-purpose interface bus.

HPPCL n. Acronym for Hewlett-Packard Printer Control Language. See Printer Control Language.

HP/UX or HP-UX n. Acronym for Hewlett-Packard UNIX. A version of the UNIX operating system specifically designed to be run on Hewlett-Packard s workstations. See also UNIX.

.hqx n. A file extension for a file encoded with BinHex. See also BinHex.

HREF n. Short for hypertext reference. An attribute in an HTML document that defines a link to another document on the Web. See also HTML.

HSB n. Acronym for hue-saturation-brightness. A color model in which hue is the color itself as placed on a color wheel, where 0 is red, 60 is yellow, 120 is green, 180 is cyan, 240 is blue, and 300 is magenta; saturation is the percentage of the specified hue in the color; and brightness is the percentage of white in the color. Also called: HLS, HSV, hue. See also color model. Compare CMY, RGB.

HSM n. Short for Hierarchical Storage Management.. A technology for managing online data and data storage in which the medium on which the information resides is linked to the frequency with which the information is accessed. By migrating data to and from primary (rapidly accessed but expensive) and secondary (slower but less expensive) storage, HSM maintains often-used information on primary storage media and less frequently used data on secondary storage such as tape or an optical jukebox. Although information resides on different storage media, all of it appears to be on line and remains accessible to the user. When users request data residing on secondary storage, HSM moves the information back to the primary storage medium.

HSV n. Acronym for hue-saturation-value. See HSB.

H-sync n. See horizontal synchronization.

HTCPCP n. Acronym for Hyper Text Coffee Pot Con trol Protocol. A protocol defined in jest as an April Fools Day spoof of open Internet standards. HTCPCP/1.0 was proposed in RFC 2324 on April 1, 1998 by Larry Masinter of Xerox PARC. In this RFC, Masinter described a protocol for controlling, monitoring, and diagnosing coffee pots.

.htm n. The MS-DOS/Windows 3.x file extension that identifies Hypertext Markup Language (HTML) files, most commonly used as Web pages. Because MS-DOS and Windows 3.x cannot recognize file extensions longer than three letters, the .html extension is truncated to three letters in those environments. See also HTML.

.html n. The file extension that identifies Hypertext Markup Language (HTML) files, most commonly used as Web pages. See also HTML.

HTML n. Acronym for Hypertext Markup Language. The markup language used for documents on the World Wide Web. A tag-based notation language used to format documents that can then be interpreted and rendered by an Internet browser. HTML is an application of SGML (Standard Generalized Markup Language) that uses tags to mark elements, such as text and graphics, in a document to indicate how Web browsers should display these elements to the user and should respond to user actions such as activation of a link by means of a key press or mouse click. HTML 2, defined by the Internet Engineering Task Force (IETF), included features of HTML common to all Web browsers as of 1994 and was the first version of HTML widely used on the World Wide Web. HTML+ was proposed for extending HTML 2 in 1994, but it was never implemented. HTML 3, which also was never standardized or fully implemented by a major browser developer, introduced tables. HTML 3.2 incorporated features widely implemented as of early 1996, including tables, applets, and the ability to flow text around images. HTML 4, the latest specification, supports style sheets and scripting languages and includes internationalization and accessibility features. Future HTML development will be carried out by the World Wide Web Consortium (W3C). Most Web browsers, notably Netscape Navigator and Internet Explorer, recognize HTML tags beyond those included in the present standard. See also .htm, .html, SGML, tag (definition 3), Web browser.

HTML attribute n. A value within an HTML tag that assigns additional properties to the object being defined. Some HTML editing software assigns some attributes automatically when you create an object such as a paragraph or table.

HTML code fragment n. HTML code that you add to a Web page to create features such as a script, a counter, or a scrolling marquee. Often used in the context of webrings to add a link and standard graphics or automation to an individual page to indicate membership.

HTML document n. A hypertext document that has been coded with HTML. See Web page.

HTML editor n. A software program used to create and modify HTML documents (Web pages). Most HTML editors include a method for inserting HTML tags without actually having to type out each tag. A number of HTML editors will also automatically reformat a document with HTML tags, based on formatting codes used by the word processing program in which the document was created. See also tag (definition 3), Web page.

HTML extensions n. A feature or setting that is an extension to the formal HTML specification. Extensions may not be supported by all Web browsers, but they may be used widely by Web authors. An example of an extension is marquee scrolling text.

HTML page n. See Web page.

HTML server control n. An ASP.NET server control that belongs to the System.Web.UI.HtmlControls namespace. An HTML server control maps directly to an HTML element and is declared on an ASP.NET page as an HTML element marked by a runat=server attribute. In contrast to Web server controls, HTML server controls do not have an <asp:ControlName> tag prefix. See also Web server control.

HTML source n. See source (definition 2).

HTML source file n. See source (definition 2).

HTML tag n. See tag (definition 3).

HTML validation service n. A service used to confirm that a Web page uses valid HTML according to the latest standard and/or that its hyperlinks are valid. An HTML validation service can catch small syntactical errors in HTML coding as well as deviations from the HTML standards. See also HTML.

HTTP n. Acronym for Hypertext Transfer Protocol. The protocol used to carry requests from a browser to a Web server and to transport pages from Web servers back to the requesting browser. Although HTTP is almost universally used on the Web, it is not an especially secure protocol.

HTTPd n. Acronym for Hypertext Transfer Protocol Daemon. A small, fast HTTP server that was available free from NCSA. HTTPd was the predecessor for Apache. Also called: HTTP Daemon. See also Apache, HTTP server, NCSA (definition 1).

HTTP Daemon n. See HTTPd.

HTTP Next Generation n. See HTTP-NG.

HTTP-NG n. Acronym for Hypertext Transfer Protocol Next Generation. A standard under development by the World Wide Web Consortium (W3C) for improving performance and enabling the addition of features such as security. Whereas the current version of HTTP establishes a connection each time a request is made, HTTP-NG will set up one connection (which consists of separate channels for control information and data) for an entire session between a particular client and a particular server.

HTTPS n. 1. Acronym for Hypertext Transfer Protocol Secure. A variation of HTTP that provides for encryption and transmission through a secure port. HTTPS was devised by Netscape and allows HTTP to run over a security mechanism known as SSL (Secure Sockets Layer). See also HTTP, SSL. 2. Web server software for Windows NT. Developed by the European Microsoft Windows NT Academic Centre (EMWAC) at the University of Edinburgh, Scotland, it offers such features as WAIS search capability. See also HTTP server, WAIS.

HTTP server n. 1. Server software that uses HTTP to serve up HTML documents and any associated files and scripts when requested by a client, such as a Web browser. The connection between client and server is usually broken after the requested document or file has been served. HTTP servers are used on Web and Intranet sites. Also called: Web server. See also HTML, HTTP, server (definition 2). Compare application server.. 2. Any machine on which an HTTP server program is running.

HTTP status codes n. Three-digit codes sent by an HTTP server that indicate the results of a request for data. Codes beginning with 1 respond to requests that the client may not have finished sending; with 2, successful requests; with 3, further action that the client must take; with 4, requests that failed because of client error; and with 5, requests that failed because of server error. See also 400, 401, 402, 403, 404, HTTP.

HTTP streaming n. The process of downloading streaming digital media using an HTTP server (a standard Internet server) rather than a server designed specifically to transmit streaming media. HTTP streaming downloads the media file onto a computer, which plays the downloaded file as it becomes available. See also real-time streaming.

hub n. In a network, a device joining communication lines at a central location, providing a common connection to all devices on the network. The term is an analogy to the hub of a wheel. See also active hub, switching hub.

hue n. In the HSB color model, one of the three characteristics used to describe a color. Hue is the attribute that most readily distinguishes one color from other colors. It depends on the frequency of a light wave in the visible spectrum. See also color model, HSB. Compare brightness, saturation (definition 2).

Huffman coding n. A method of compressing a given set of data based on the relative frequency of the individual elements. The more often a given element, such as a letter, occurs, the shorter, in bits, is its corresponding code. It was one of the earliest data compression codes and, with modifications, remains one of the most widely used codes for a large variety of message types.

human engineering n. The designing of machines and associated products to suit the needs of humans. See also ergonomics.

human-machine interface n. The boundary at which people make contact with and use machines; when applied to programs and operating systems, it is more widely known as the user interface.

hung adj. See hang.

hybrid circuit n. A circuit in which fundamentally different types of components are used to perform similar functions, such as a stereo amplifier that uses both tubes and transistors.

hybrid computer n. A computer that contains both digital and analog circuits.

hybrid microcircuit n. A microelectronic circuit that combines individual microminiaturized components and integrated components.

hybrid network n. A network constructed of different topologies, such as ring and star. See also bus network, ring network, star network, Token-Ring network, topology.

Hybris virus n. A slow-spreading but persistent self-updating Internet worm first detected in late 2000. The Hybris virus is activated whenever an infected computer is connected to the Internet. It attaches itself to all outgoing e-mail messages, maintains a list of all e-mail addresses in the headers of incoming e-mail messages, and sends copies of itself to all e-mail addresses on the list. Hybris is difficult to eradicate because it updates itself regularly, accessing and downloading updates and plug-ins from anonymous postings to the alt.comp.virus newsgroup. Hybris incorporates downloaded extensions into its code, and it e-mails its modified form to additional potential victims. Hybris often includes a spiral plug-in which produces a spinning disk on top of any active windows on a user s screen.

HyperCard n. An information-management software tool, designed for the Apple Macintosh, that implements many hypertext concepts. A HyperCard document consists of a series of cards, collected into a stack. Each card can contain text, graphical images, sound, buttons that enable travel from card to card, and other controls. Programs and routines can be coded as scripts in an object-oriented language called HyperTalk or developed as external code resources (XCMDs and XFCNs). See also hypertext, object-oriented programming, XCMD, XFCN.

hyperlink n. A connection between an element in a hypertext document, such as a word, a phrase, a symbol, or an image, and a different element in the document, another document, a file, or a script. The user activates the link by clicking on the linked element, which is usually underlined or in a color different from the rest of the document to indicate that the element is linked. Hyperlinks are indicated in a hypertext document through tags in markup languages such as SGML and HTML. These tags are generally not visible to the user. Also called: hot link, hypertext link, link. See also anchor (definition 2), HTML, hypermedia, hypertext, URL.

hypermedia n. The combination of text, video, graphic images, sound, hyperlinks, and other elements in the form typical of Web documents. Essentially, hypermedia is the modern extension of hypertext, the hyperlinked, text-based documents of the original Internet. Hypermedia attempts to offer a working and learning environment that parallels human thinking that is, one in which the user can make associations between topics, rather than move sequentially from one to the next, as in an alphabetic list. For example, a hypermedia presentation on navigation might include links to astronomy, bird migration, geography, satellites, and radar. See also hypertext.

hyperspace n. The set of all documents that can be accessed by following hyperlinks in the World Wide Web. Compare cyberspace (definition 2), Gopherspace.

HyperTalk n. A programming language used to manipulate HyperCard stacks developed by Apple Computer, Inc. See also HyperCard.

hypertext n. Text linked together in a complex, nonsequential web of associations in which the user can browse through related topics. For example, in an article with the word iron, traveling among the links to iron might lead the user to the periodic table of the elements or a map of the migration of metallurgy in Iron Age Europe. The term hypertext was coined in 1965 to describe documents presented by a computer that express the nonlinear structure of ideas as opposed to the linear format of books, film, and speech. The term hypermedia, more recently introduced, is nearly synonymous but emphasizes the nontextual element, such as animation, recorded sound, and video. See also HyperCard, hypermedia.

Hyper Text Coffee Pot Control Protocol n. See HTCPCP.

hypertext link n. See hyperlink.

Hypertext Markup Language n. See HTML.

Hypertext Transfer Protocol n. See HTTP.

Hypertext Transfer Protocol Daemon n. See HTTPd.

Hypertext Transfer Protocol Next Generation n. See HTTP-NG.

HyperWave n. A World Wide Web server that specializes in database manipulation and multimedia.

hyphen n. A punctuation mark (-) used to break a word between syllables at the end of a line or to separate the parts of a compound word. Word processing programs with sophisticated hyphenation capabilities recognize three types of hyphens: normal, optional, and nonbreaking. Normal hyphens, also called required or hard hyphens, are part of a word s spelling and are always visible, as in long-term. Optional hyphens, also called discretionary or soft hyphens, appear only when a word is broken between syllables at the end of a line; they are usually supplied by the word processing program itself. Nonbreaking hyphens are always visible, like normal hyphens, but they do not allow a line break. See also hyphenation program.

hyphenation program n. A program (often included as part of a word processing application) that introduces optional hyphens at line breaks. A good hyphenation program will avoid ending more than three lines in a row with hyphens and will prompt the user for confirmation or tag ambiguous breaks, as in the word desert (did the army de-sert in the des-ert?). See also hyphen.

hysteresis n. The tendency of a system, a device, or a circuit to behave differently depending on the direction of change of an input parameter. For example, a household thermostat might turn on at 68 degrees when the house is cooling down, but turn off at 72 degrees when the house is warming up. Hysteresis is important in many devices, especially those employing magnetic fields, such as transformers and read/write heads.

HYTELNET n. A menu-driven index of Internet resources that are accessible via telnet, including library catalogs, databases and bibliographies, bulletin boards, and network information services. HYTELNET can operate through a client program on a computer connected to the Internet, or through the World Wide Web.

HyTime n. Acronym for Hypermedia/Time-based Structuring Language. A markup language standard that describes links within and between documents and hypermedia objects. The standard defines structures and some semantic features, enabling description of traversal and presentation information of objects.

Hz n. See hertz.