HAL

n. See hardware abstraction layer.

half-duplex

adj. Of or pertaining to two-way communication that takes place in only one direction at a time. For example, communication between people is half-duplex when one person listens and waits to speak until the other has finished speaking. Compare duplex¹.

half-duplex transmission

n. Two-way electronic communication that takes place in only one direction at a time. Compare duplex², simplex transmission.

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.

handheld computer

n. A computer small enough to be held in one hand while being operated by 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 PC

n. A computer that is small enough to fit in a jacket pocket and that can run, for example, Microsoft Windows CE (a scaled-down version of Windows 95) and applications made for that operating system. Compare handheld computer, PDA. Acronym: HPC.

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.

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.

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 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. Also called hard disk drive. Compare floppy 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 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.

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, 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. See also application programing interface, device independence. Acronym: HAL.

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 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 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.

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.

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.

HDTV

n. Acronym for high-definition television. A method of transmitting and receiving television signals that produces a picture with much greater resolution and clarity than does standard television technology. International standards for HDTV are not yet established.

help

n. 1. The capability of many application programs to display advice or instructions for using their features when so requested by the user, as by a screen button or 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. Although help facilities are not usually as extensive as manuals, they give the user a means of refreshing the memory and may also offer the more advanced user quick access to details on little-used program features. 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.

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 or 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 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 contrls, plug-in (definition 2).

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).

hertz

n. Abbreviated Hz. 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 = 1,000 Hz = 10³ Hz), megahertz (MHz = 1,000 kHz = 10⁶ Hz), gigahertz (GHz = 1,000 MHz = 10⁹ Hz), or terahertz (THz = 1,000 GHz = 10¹² Hz).

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.

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.

hierarchical

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

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 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. 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 5.0 and later) can move portions of itself into the high memory area, thereby increasing the amount of conventional memory available for applications. See also conventional memory, expanded memory. Acronym: HMA.

high tech

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

HIPPI

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

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), record¹. 3. Retrieval of a document, such as a home page, from a Web site.

HKEY

n. Short for handle key. In Windows 95, 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_USER\Control Panel leads to the subkey for the Windows Desktop. See also handle (definition 1).

HLS

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

home

n. A beginning position, such as the top 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.

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 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 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.

homogeneous network

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

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).

host

n. The main computer in a system of computers or terminals connected by communications links.

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.

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 timed out

n. An error message returned by a server when the host machine that contains the requested information fails to return a response within a set time limit. Some UNIX servers will close timed-out sessions to manage system resources.

host unreachable

n. An error message indicating that a server has failed to connect to the requested host. This may be because the server does not know the host's address, the host may be down, or the host is refusing the connection.

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 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.

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.

HotWired

n. A Web site affiliated with Wired magazine that contains news, gossip, and other information about the culture of the Internet: http://www.hotwired.com/frontdoor/.

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.

HP/UX

n. Acronym for Hewlett-Packard UNIX. A version of UNIX developed by Hewlett-Packard for use on their workstations.

HREF

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

HTML+

n. An unofficial specification for enhancements to the original HTML, such as forms and tables. HTML+ was not adopted as a standard but influenced the HTML 2.0 and HTML 3.2 standards. See also HTML.

HTML

n. Acronym for Hypertext Markup Language. The markup language used for documents on the World Wide Web. HTML is an application of SGML 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 2.0, defined by the Internet Engineering Task Force (IETF), includes features of HTML common to all Web browsers as of 1995 and was the first version of HTML widely used on the World Wide Web. Future HTML development will be carried out by the World Wide Web Consortium (W3C). HTML 3.2, the latest proposed standard, incorporates features widely implemented as of early 1996. 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 2.0

n. A revised version of the HTML specification that added the capability for forms and eliminated certain little-used tags. Produced as an Internet Draft in mid-1994, HTML 2.0 represented common practice among browser developers at the time. It was standardized as an RFC in November 1995. See also HTML+, HTML, HTML 3.0, HTML 3.2, RFC.

HTML 3.0

n. A revised version of the HTML specification. Its primary enhancement to HTML 2.0 is the support of tables. HTML 3.0 was never standardized or fully implemented by a major browser developer. See also HTML+, HTML, HTML 2.0, HTML 3.2.

HTML 3.2

n. A World Wide Web Consortium (W3C) recommendation for an HTML standard that supersedes the proposed HTML 3.0 standard and adds features to HTML 2.0 such as applets, sub- and superscripts, tables, and text flow around images. See also HTML, HTML 2.0, HTML 3.0.

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 attribute

n. A name-value pair used within an HTML tag to assign additional properties to an object being defined.

HTML tag

n. A symbol used in HTML to identify a page element's type, format, and appearance.

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 client/server protocol used to access information on the World Wide Web. See also URL.

HTTPd

n. A small, fast HTTP server available free from NCSA. See also HTTP server, NCSA (definition 1).

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. Web server software for Windows NT. Developed by the European Microsoft Windows NT Academic Centre (EMWAC) at the University of Edinburgh, Scotland, it is available for download and 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). 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.

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).

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.

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, phrase, symbol, or image, and a different element in the document, another hypertext 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. See also anchor (definition 2), HTML, hypermedia, hypertext, URL.

hypermedia

n. Any nontextual element, such as animation, recorded sound, images, or video that links to other information. 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. The programming language used to manipulate HyperCard stacks. 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. See also hypermedia.

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.

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.

Hz