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(1) A person who mostly employs trial and error as the basis for designing and building programs or for accessing computer-based systems. Frequently the work of the hacker is unmaintainable. (2) A person who uses his or her knowledge and means to gain unauthorized access to protected resources.

hardware abstraction layer.

half card:
Synonym for short card.

In data communications, pertaining to an alternating, one-way-at-a-time, independent transmission.

half-duplex transmission:
Data transmission in either direction, one direction at a time.

A contiguous sequence of bits or characters that comprises half a computer word and that is capable of being addressed as a unit.

A circular band of light around exceptionally bright objects in an image. A halo can be an undesirable characteristic of some imaging devices.

halt instruction:
An instruction that specifies the suspension of a program and a return of control to the operating system.

Hamming code:
An error-detecting and error-correcting binary code used in data transmission that can
  1. detect all single- and double-bit errors and
  2. correct all single-bit errors.
A Hamming code satisfies the relation 2m> m+k+1, where: m is the number of check bits in the block; k is the total number of information bits in the block; and where n = m + k and n is the total number of bits in the block.

Hamming distance:
The minimum number of bit transitions required to change any valid data block into another valid data block.

hand-held calculator:
Synonym for pocket calculator.

hand-held scanner:
A scanner where the user passes the scan head over the medium being scanned, such as a piece of paper.

(1) In computer graphics, a small rectangular box that may appear on one of the corners or in the middle of the side of a bounding box or a window, and that is used to resize the graphic object or the window. (2) In programming, an abridged form of handle an exception

handle an exception:
To take direct action as the result of the occurence of an exception. Action is normally taken as a result of transferring control to an exception handler.

Protocols and procedures used by two devices for establishing communications.

Pertaining to sensations of touch, pressure, temperature, twist, etc., mediated by skin, muscle, tendons, or joints. Haptic represents tactile senses, but are not limited to them.

haptic display:
In virtual reality, a computer-controlled object within a virtual world with assigned force fields, torque, friction, heat, and pressure that are made noticeable to a person interacting with the object.

hard copy:
(1) A permanent copy of machine output in a visually readable form, generated on a device such as a printer or plotter; for example, printed reports, listings, documents, and summaries. (2) A permanent copy of a display image generated on an output unit such as a printer or a plotter, and that can be carried away. Contrast with soft copy.

hard disk:
(1) A magnetic disk of rigid, rather than flexible, material. (2) Deprecated synonym for hard disk drive.

hard disk drive (HDD):
A magnetic storage device that uses hard disks. Typical hard disk drives use multiple hard disks mounted on a single spindle. Synonymous with hard drive.

hard drive:
Synonym for hard disk drive.

hard error:
A permanent error that always recurs on successive attempts to read data.

hard hyphen:
A hyphen required by the spelling of a word or an expression regardless of its position in a line. Hard hyphens are not subject to hyphen drop. Synonymous with required hyphen. Contrast with soft hyphen.

hard page break:
A page break entered manually in a selected position that does not change during automatic pagination. Synonymous with forced page break. Contrast with soft page break.

hard sectoring:
The physical marking of sector boundaries on a magnetic disk. Contrast with soft sectoring.

hard space:
A space represented by a special character in a character string at which a text processor will not divide the string. Synonymous with no-break space.

Any physical component capable of data processing; for example, computers, peripheral equipment. Contrast with software.

hardware abstraction layer (HAL):
A set of subprograms that translates various vendors' hardware characteristics to a common set of specifications to optimize the portability of an operating system.

hardware design language (HDL):
A design language with special language constructs and, sometimes, verification protocols, used to develop, analyze, and document a hardware design.

hardware interrupt:
A request for some service from the central processing unit, generated either externally by a device such as a disk or an input/output port, or internally by the processing unit itself. If the hardware interrupt is accepted, the processor suspends its current operation, saves the status of its work, and transfers control to a specified routine known as an interrupt handler.


hartley (Hart):
A unit of logarithmic measure of information expressed as a logarithm to base 10. For example, the decision content of a character set of eight characters equals 0.903 hartley (log108 = 0.903). The base of the logarithm determines the unit used. Contrast with natural unit, shannon.

hash addressing:
Synonym for hashing.

hash clash:
Synonym for collision (in hashing).

hash function:
In hashing, a function used to determine the position of a given item in storage to make more efficient use of that storage. The hash function operates on a selected field, the key, in each item and is used to map the set of keys to a usually much smaller set of storage positions; therefore this mapping is usually a many-to-one map.

A method of transforming a search key into an address for the purpose of storing and retrieving data. The method is often designed to minimize the search time. Synonymous with hash addressing.

hash-table search:
A search in which the storage location of a desired data element is derived from a hash table, and an appropriate procedure is followed in case of an address collision.

hash value:
The number generated by a hash function to indicate the position of a given item in storage.

head/disk assembly.

hard disk drive.

hardware design language.

high-level data link control.

header label.

head crash:
A contact of a magnetic head with the surface of a moving data medium, damaging the data medium, the magnetic head, or both.

head/disk assembly (HDA):
In a disk drive, an assembly that includes magnetic disks, magnetic heads, and an access mechanism all enclosed in a container.

In a broadband LAN, a device that receives signals from each data station and retransmits them to all data stations. The retransmission may require a shift of carrier frequencies.

The control data that precedes user data such as in electronic mail, in HTML pages, and in protocol data units. In electronic mail, it contains date and time, sender and addressee, subject, and structure of message content. In an HTML page it typically contains title, character set identification, content description, keywords for search engines, and identifies the software used to generate the document. In protocol data units at a given protocol layer, it precedes the data being passed from (or to) a protocol entity of the next higher layer and contains control information relating to the protocol exchange with the corresponding protocol entity at the same level. Synonymous with envelope (in electronic mail).

header label (HDR):
An internal label that identifies a file, marks its location, and contains data for use in file control. Synonymous with beginning-of-file label.

head gap:
Synonym for flying height.

In ASCII and data communication, a sequence of characters preceded by the start-of-heading character that is used as the machine-sensible address or as routing information.

head loading zone:
A peripheral area on each magnetic disk surface where magnetic heads are positioned to the proper flying height for reading and writing data.

head-mounted display (HMD):
In virtual reality, a head-supported device including a three-dimensional display, position and orientation captors, and sometimes also earphones.

head-related transfer function (HRTF):
In virtual reality, the transfer function that transforms head movement data into spacial location for sound.

head switching:
Changing from one read/write head to another.

(1) A part of internal storage used for dynamically building or deleting data objects, where the order of using the data objects is undefined. (2) The set of data objects in a heap.

Hebbian learning:
In artificial neural networks, learning that increases the connection weight of a neural connection if the two artificial neurons are activated synchronously and decreases the connection weight if the artificial neurons are activated asynchronously. In the simplest case, the amount of change of the connection weight is proportional to the product of the two output values.

The maximum number of nodes in any path leading from the root node to a terminal node.

Helsinki principle:
In a conceptual schema language, any meaningful exchange of utterances that depends upon the prior existence of an agreed-upon set of semantic and syntactic rules.

The structure of a system whose components can communicate directly with each other.

heterogeneous computer network:
A computer network in which computers have dissimilar architectures but are able to communicate with each other. Synonymous with heterogeneous network.

heterogeneous network:
Synonym for heterogeneous computer network.

heuristic learning:
A learning strategy developed from results of experimentation, of evaluation, or of trial-and-error methods.

heuristic method:
A problem solving method, based on experience and judgment, used to obtain practical results without guarantee of completeness or correctness. For example, an exploratory method of solving problems in which an evaluation is made of the progress towards an acceptable final result using a series of approximate results.

heuristic rule:
An ad hoc rule written to formalize the knowledge and experience an expert uses to solve a problem.

Characterized by a selection, choice, or condition that has sixteen possible different values or states, such as the hexadecimal digits.

hexadecimal digit:
A digit used in the hexadecimal system; for example: the graphic characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F .

hexadecimal numeral:
A numeral in the hexadecimal system.

hexadecimal numeration system:
Synonym for hexadecimal system.

hexadecimal system:
The fixed-radix notation that uses the sixteen digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F, where the digits A, B, C, D, E, and F correspond to the decimal numerals 10, 11, 12, 13, 14, and 15, a fixed radix of sixteen, and the lowest integral weight of 1. For example, in the hexadecimal system, the numeral 3E8 represents 3 x 162 + 14 x 161 + 8 x 160 equivalent to the decimal numeral 1000. Synonymous with hexadecimal numeration system.

hidden character:
A character that is not normally printed, displayed, or intended to be printed. For example, an embedded control character.

hidden layer:
In artificial neural networks, a layer whose artificial neurons do not directly communicate with external systems.

hidden line:
A line or a segment of a line that can be masked in a view of a three-dimensional object.

hidden Markov model (HMM):
In speech recognition, a model in which the state of each speech segment is represented as a state in a Markov process and in which these states are not directly observable. To recognize an utterance, the speech recognizer computes the likelihood that it was generated by each of the models derived during training. The utterance is recognized as the word or syntagma whose model gives the highest likelihood score.

hidden neuron:
An artificial neuron that does not directly communicate with external systems.

hidden surface:
A surface of an opaque three-dimensional object that would not be visible when the object is viewed from a particular angle; for example, the backside of the moon.

hierarchical artificial neural network:
Synonym for hierarchical neural network.

hierarchical computer network:
A computer network in which the nodes are organized in a hierarchy of classes with respect to their capability of control or operation.

hierarchical data model:
The data model that provides a tree structure for relating data elements, where each node of the tree corresponds to a group of data elements or a record type, and may have only one superior node.

hierarchical network:
A network whose components are ranked into levels of subordination according to specific rules.

hierarchical neural network:
An artificial neural network consisting of several stages of subnetworks, in which the processing occurs from one stage to the next. Synonymous with hierarchical artificial neural network.

hierarchical planning:
A planning technique that refines the vague parts of a plan into more detailed subplans by generating a hierarchical representation of it.

The structure of a system whose components are ranked into levels of subordination according to specific rules.

hierarchy chart:
Synonym for structure chart (in programming).

high-density diskette:
Any floppy disk operating at a higher capacity than when the first disks of the same form factor were introduced into production. The typical 3.5 inch floppy disks operating at 1.44 megabytes are characterized as "double-sided high-density" or "2 HD".

high-level data link control (HDLC):
Control of data links by means of a bit-oriented protocol using the frame structure defined in ISO/IEC 3309:1993 Information Technology -- Telecommunications And Information Exchange Between Systems -- High-Level Data Link Control (HDLC) Procedures -- Frame Structure.

high-level language:
A programming language that is primarily designed for, and syntactically oriented to, particular classes of problems and that is essentially independent of the structure of a specific computer or class of computers; for example, Ada, COBOL, Fortran, Pascal. Synonymous with high-order language. (Figure 2 - Hierarchy of language).

high-level processing:
In computer vision, image processing requiring a computer to simulate human intelligence.

high-level vision:
Computer vision that includes processes that simulate cognition.

Emphasizing a display element by modifying its visual attributes.

high-order language (HOL):
Synonym for high-level language.

high-speed carry:
In parallel addition, any procedure for speeding up the processing of carries, for example: standing-on-nines carry.

In a process computer system, the means for interconnection between the computer system and the process interface system. A bus may be used as a highway.

(1) The successful identification of one or more data items that satisfy specified selection criteria. Contrast with match. (2) A transient disturbance to a transmission medium.

head-mounted display.

hidden Markov model.

high-order language.

hold-for-delivery service:
A service that enables a recipient's user agent to request that the message transfer system holds its messages and reports for delivery until a later time.

hold mode:
That mode of an analog computer during which integration is stopped and all variables are held at the values they had when this mode was entered.

hole pattern:
An array of holes that implements on a data medium the coded representation of data; for example, a punching configuration that implements the representation of a single character.

Pertaining to a particular type of code or punch card that utilizes 12 positions per column and usually 80 columns per card.

home address:
The information written on a magnetic disk that identifies the track numbers.

home page:
A Web page at a network site that acts as the starting point for navigation.

homogeneous computer network:
A computer network in which all computers have a similar or the same architecture. Synonymous with homogeneous network.

homogeneous network:
Synonym for homogeneous computer network.

One of a set of identical terms that refer to different entities.

Hopfield network:
In artificial neural networks, a totally connected network having only visible neurons that are cyclically updated until a stable state is obtained. A Hopfield network has a finite number of stable states, corresponding to local minimums of an energy function. During learning, the connection weights are adjusted so that the stable states correspond to the patterns to be stored. After applying an input pattern, the network evolves toward the closest stored pattern. A Hopfield network may be a synchronous neural network or an asynchronous neural network. Hopfield networks are mainly used as an associative storage but also has applications in optimization. Synonymous with crossbar associative network.

horizontal format:
Synonym for landscape.

horizontal formatting:
Synonym for horizontal tabulation.

horizontal resolution:
In computer graphics, the reciprocal of the number of pixels per linear measure along a single horizontal scanning line, that is, the distance between pixel centers.

horizontal synch:
The portion of a composite video signal that controls the timing for horizontal sweep.

horizontal tabulation:
The capability of a text editor to position text horizontally to locations defined by the user.

horizontal tabulation character (HT):
A format effector that causes the print or display position to move forward to the next of a series of predetermined positions along the same line.

Synonym for host computer.

host computer:
In a computer network, a computer that provides users with services such as computation and database access and that may perform network control functions. Synonymous with host.

Synonym for content hosting.

host language:
A programming language in which statements of a data manipulation language or other specialized language are embedded.

host machine:
(1) A computer used to develop software intended for another computer. Contrast with target machine. (2) A computer used to emulate another computer. Contrast with target machine. (3) The computer on which a program or file is installed.

host name:
A name identifying one specific host computer, within a given context. Contexts include intranets where a simple name may be a request and the Internet where a fully qualified domain would be required.

host type:
Synonym for base type.

hot site:
A fully equipped computer center that provides an immediate alternative data processing capability for use in the event of a disaster.

(1) The x, y position that corresponds to the coordinates reported for a pointer. For example, the position of the tip of an arrow. (2) An icon or an active region in a hypermedia application that can be selected by a pointing device to activate a hyperlink; for example: an icon used to represent an anchor in a document. A hotspot usually is a word highlighted by underlining or other means, or a small picture. (Figure 71 - Difference between anchor and hotspot).

hot standby:
A configuration in which a redundant functional unit is kept in an operational mode so that it can be immediately brought into service should the primary functional unit fail.

head-related transfer function.

The horizontal tabulation character.

A markup language used to create hypertext documents that are portable from one platform to another. HTML is based on SGML and has generic semantics that are appropriate for representing information from a wide range of applications. HTML is the abbreviation for HyperText Mark-up Language.

Name of an application protocol providing means to transfer hypertext documents between servers and clients. HTTP is the abbreviation for Hypertext Transfer Protocol.

(1) A control feature of a disk or reel that fits onto the spindle. (2) In distributed systems, a functional unit that provides interconnectivity between multiple nodes. Hubs may be passive or include repeaters but do not provide switching or routing.

That attribute of a colored object by which it is identified as red, green, blue, etc. The hues of pure colors correlate directly with the dominant wavelength of their radiation. White, black, and grays possess no hue. Hue is one of the three attributes of color; the other are saturation and luminance.

human error:
Synonym for mistake.

human voice:
Synonym for voice.

hybrid computer:
A computer that has features that are a combination of those of a digital computer and an analog computer and that converts data between digital and analog representations.

Synonym for hypercube network.

hypercube network:
A hypergrid network the edges of which are reduced to two nodes. An n-dimensional hypercube has 2n nodes. Synonymous with hypercube.

A hyperobject consisting of an integrated set of documents where individual units of data are connected by hyperlinks. Synonymous with hypermedia document.

Synonym for hypergrid network.

hypergrid network:
A multidimensional expansion of a linear network. If n is the dimension of the hypergrid network, so there are 2(n-1) different classes of nodes; the innermost nodes are connected to 2n branches, the hypercorners to n branches. If there exist only nodes on the hypercorners then the hypergrid network is called a hypercube. Synonymous with hypergrid.

A set of hyperdocuments among which hyperlinks can be established. Synonymous with hypermedia library.

An oriented logical connection between individual units of data in a hypermedia application, that allows moving from one unit to another. At the source of a hyperlink a tag, an icon, or a region of a picture may be displayed and used as a hotspot. The target of a hyperlink may be a specific tag within a document, a general reference to a document, or a process. Synonymous with hypermedia link.

(1) Pertaining to the organization, storage, or presentation of data, with references within these data, that permit users to move from one data to another without linear searches. (2) The domain of hypermedia concepts, applications, and techniques, for example: hypertext, a Web page with embeddded video. (Figure 68 - Current usage of terms in relation to the characteristics).

hypermedia document:
Synonym for hyperdocument.

hypermedia library:
Synonym for hyperlibrary.

hypermedia link:
Synonym for hyperlink.

hypermedia navigation:
The process of moving from one hypermedia node to another by following hyperlinks.

hypermedia node:
An individual unit of data that is either the source or the target of a hyperlink.

hypermedia path:
A defined sequence of linked hypermedia nodes.

hypermedia structure:
The arrangement of data into hypermedia nodes.

hypermedia/time-based structuring language:
Synonym for HyTime.

hypermedia tool:
An application that allows authoring or presenting hypermedia.

hypermedia web:
An interconnected set of hypermedia nodes and hyperlinks. Usually the hyperlinks deal with a common topic, or can be traversed continuously through common anchors.

A multimedia representation of an object; for example: a WWW home page. (Figure 69 - Examples of object types).

An abstract environment that is constructed using hypermedia techniques. Hyperspace may have more than the usual number of dimensions and its overabundance of hyperlinks may cause disorientation to the user.

(1) A method of presenting text in discrete units, or nodes, that are connected by links for navigation. (2) Text designed to be read or accessed in a nonlinear manner using nodes that are connected by links for navigation. (Figure 68 - Current usage of terms in relation to the characteristics). (3) Synonym for hypermedia (deprecated in this sense).

hypertext markup language:

hyphenation control:
A function that enables manual or automatic determination of whether to insert or omit a hyphen.

hyphen drop:
The function that ensures that a soft hyphen does not appear in the presentation of a word when it is not necessary to divide the word.

A standard hypermedia structuring language for representing hyperlinks, temporal and spatial event scheduling, and synchronization. HyTime is an extension of SGML. Synonymous with hypermedia/time-based structuring language.

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