H

H – Hacker (computer) to Hysteresis (communications, computer)

Hacker (computer)
In the early 1960’s this term had a "good" connotation that meant all "hackers" who slaved and developed early "microcode". It still refers, in computer circles, to programmers who write programs in assembly language or in high-level languages, such as BASIC and C. Although it may refer to any programmer, it implies very tedious "hacking away" at the bits and bytes. It has fallen into disrepute since it is now used "commercially" to refer to people who break a code, gaining illegal access into a system.

Half ADDER (computer/microelectronics)
Switching circuit which combines binary bits to generate the SUM and the CARRY. It can only take in the two binary bits to be added and generate the SUM and CARRY.

Half-Duplex (communications)
Transmission of data in both directions, but only one direction at a time. Two-way radio was the first to use half-duplex, for example, while one party spoke, the other party had to listen and wait their turn (“over” - - - - “over and out”---- etc.). Contrast with full duplex.

Half Height Drive (computer)
Disk drive mechanism that only takes up half the vertical height space of earlier drives.

Half Shift Register (computer/microelectronics)
Another name for certain types of flip-flop gates when used with a shift register. It takes two of these to make one stage in a shift register.

Halftone (A/V, computer/printer)
In printing, the simulation of a continuous-tone image (shaded drawing, photograph) with groups of dots. All printing processes, except for Cycolor, print dots. The smaller the dots and the wider they are spaced apart, the lighter the image. The denser the dots, the darker the image. If one looks at a newspaper or magazine photo through a magnifying glass, they can see how different dot densities simulate continuous shades.

In Audio Visual terms, the pitch interval between a note with a sharp or a flat and the adjacent whole tone. the difference between G# and A is a half-tone, also called a half step.

Half Track (A/V, production)
Audiotape recorder, or recording, that uses one-half the width of the tape for an audio signal on the first pass, and the other half on the reverse pass.

Hall Effect (computer/microelectronics)
Development of a transverse electric potential gradient in a current-carrying conductor placed in a magnetic field when the conductor is positioned so that the direction of the magnetic field is perpendicular to the direction of current flow. Analysis of the Hall effect yields important information on the band structure of metals and semiconductors and on the nature of the conductivity process. In semiconductor research, the magnitude of the Hall effect in simple cases provides a direct estimate of the concentration of charge carriers. The Hall effect is one of the so-called galvanomagnetic effects.


Halo (A/V, production)
Dark or coloured flare around a very bright light source or a highly reflecting object.

Halogen Metal Iodide Lamp: HMI (A/V, production)
Extremely efficient, high intensity light burning at 5,600 degrees Kelvin, (outdoor illumination). It needs an additional piece of equipment, a ballast, to operate properly.

Hammer (computer/printing)
Printing mechanism in an impact printer that pushes the typeface onto a ribbon and paper, or that pushes the paper into the ribbon and the typeface.

Hamming Code (communications)
Error correction code that is interspersed with the bits of each character. At the receiving station, the code is checked in order to detect missing bits.

Handle (computer/Windows)
Tiny square which is attached to a graphic image (on the screen) that is used for moving or reshaping the image. The handle is selected by moving the cursor onto it and pressing a key or mouse button. Also describes an unassigned integer assigned by Windows to uniquely identify an instance (occurrence) of a module (application, hModule), task (hTask), window (hWnd) or device context (hDC) or a graphic object.

Handler (computer)
Software routing that performs a particular task, for example, upon detection of an error, an error handler is called upon to recover from the error condition.

Hand Props (A/V, production)
Objects, called properties, that are handled by the performer.

Handset (computer)
Device at the end of the cord on a telephone set that contains the speaker and the microphone, where the voice pickup still remains as an analog function (not digitized as yet).

Handshaking (communications/Windows)
Exchange of predetermined sequences of control signals or control characters between two devices or systems to establish a connection, or to break a connection, or to exchange data and status information, is commonly referred to as handshaking. For personal computers using Windows, a flow control, or "go-ahead" signal sent by the local computer to a remote computer when using a communication program such as Terminal, in Windows. XON/XOFF is a standard software handshaking.. It is not used with remote systems that use a hardware handshaking method.

Hanging Indentation (computer/printing)
In text processing, a paragraph style in which all lines except the first are indented.

Hanging Paragraph (computer/printing)
Paragraph of a text where the first line starts at the left margin, but the remaining lines are indented (same as hanging indentation).

Happy Talk (A/V, production)
Banter between or among anchor persons during a newscast.

Hard card (computer)
Board that provides the capacity of a 20 to 100 megabyte hard disk. A hard card fits into an expansion slot inside a personal computer.

Hard Coded (computer)
Software that performs a fixed number of applications or works with a fixed number of devices. It can be a program written to work with only two types of plotters, that does not allow any substitutions. Hard code applications may run faster but can be inflexible for future applications.

Hard Copy (A/V, computer)
In audio/visual terms, the computer printout showing in typewritten form all editing decisions of the completed helical scan (tape) workprint or the master tape (soft copy information appears only on the computer screen). In computer terms, Output from a computer in permanent printed form.

Hard Disk (computer)
Inflexible disk; hard disks are usually in a pack, often in a sealed module.

Hard Error (computing)
Permanent, unrecoverable error: a group of errors that requires user intervention and includes disk read errors (fail?, retry?, abort?) and printer errors (printer jam?).

Hard Magnetic Disk (computer)
Disk platter coated with magnetic oxide and used for magnetic storage.

Hard Return (computer/printing)
Embedded or control code within a text or document that is inserted by pressing the Enter key (like a carriage or ball-element return on an electric typewriter). Hard returns may be invisible until a reveal-function is invoked which would then indicate all the hard returns (along with any other control codes) (retained feature of Corel, WordPerfect).

Hard Sectored Disk (computer)
Older, no longer used format with a hole in front of each sector, near the centre of the disk.

Hardware (computer)
Physical equipment and components forming a computer system.

Hardware Descriptive Language (computer)
Notations and languages that facilitate the documentation, design, simulation, and manufacturing of digital computer system.

Hardware Failure (computer)
Failure with the physical elements of a system rather than software.

Hardware Interrupt (computer)
Interrupt caused by a hardware device (printer, keyboard, touch-screen monitor).




Hardware Key (computer)
Copy protection device supplied with software that plugs between the computer port and the attached device (inserted between). The software requests the key serial number during execution to verify its existence, and it acts as a pass-through but tests for codes that read the serial number (trademark model is called a "dongle").

Hardware Monitor (computer)
Device used for measuring electrical events (pulses, voltage levels, etc.) in a digital computer. It is useful for gathering data for measurement and evaluation of computer systems, particularly when used in conjunction with software monitoring. Most are external, general-purpose, but in principle they could be built into a computer if it were economically justifiable.

Hard Wired Logic (computer/microelectronics)
Group of logical circuits permanently interconnected to perform a specific function.

Harmonic Analyzer (communications/microelectronics)
Device for separating and measuring the frequencies and amplitudes of the Fourier-series components of a complex periodic wave. A complete harmonic analysis would include finding the phase of each component; some analyzers do this especially the "rolling sphere" devices, now largely of historical interest. Most electrical analyzers find component amplitude only (see nonsinusoidal waveform).

Harmonic Distortion (communications)
Frequencies that are generated as multiples of the original frequency due to irregularities in the transmission facility or equipment or technique (radio waves, wire, etc.).

Hashing (computer)
Describes a general class of operations done to transform one or more fields (usually a key) into a different (usually more compact) arrangement. Hashing may have been first used because it seemed that "hash" was being made out of integral pieces of data. The rationale for hashing derives from being able to convert naturally occurring, ill-structured, scattered key fields into easily manipulated fields. In less complex applications, hashing can be the ability to apply a formula to a record key to yield a number that represents a disk address (also called randomizing).

Hash Total (computer)
Totalling of data in fields to determine the accuracy of processing information, including fields not normally used in calculations. At various stages in processing the hash total is recalculated and compared with the original, and, if any information has been changed or lost, the mismatch will signal an error to the user and the application.

Hayes-Compatible Modem (communications, computer)
Modems that use the command set originated for the Hayes Smartmodem that became an industry-wide, de facto standard (Hayes Microcomputer Products, Inc.).

HDLC (communications)
High-level Data Link Control - International communications protocol defined by ISO and used in X.25 packet switching networks. HDLC provides error correction at the data link layer. SDLC (IBM), LAP, and LAPB are all subsets of HDLC. The protocol defines standards for linking Data Terminal Equipment and Data Communications Equipment.

HDTV (A/V, communications, computer)
High Definition Television - form of television transmission that results in clearer images, especially on large screen sets. Japanese television producers have established their own standard for HDTV under PAL. A standard for the U.S. version of HDTV, using digital sampling techniques related to techniques for audio sampling, is now being deployed. Basically, the technique doubles the lines of resolution of the current 525 line NTSC standard. In effect, using today's broadcast system, it would mean using two television channels to transmit HDTV information, and then re-integrating the channels at the TV.

Head Assembly (A/V)
In Audio head assembly: small electromagnet that erases the signal from the tape (erase head); puts the signals on the audiotape (recording head); and reads them off the tape (playback head). In Video head assembly: the electromagnet puts electronic signals on the videotape or reads the signals off the tape. Video heads are usually in motion.

Head Crash (computer)
Physical destruction of a hard disk. Due to head misalignment or contamination with dust and dirt, the read/write head collides with the disk's recording surface. The data is destroyed, and both the disk platter and read/write head usually have to be replaced. The read/write head touches the surface of a floppy disk, but on a hard disk, it hovers above its surface at a distance that is less than the diameter of a smoke particle. For example, a read/write head flying over the disk surface would be like a 3-stage rocket flying above a highway six inches above the surface at 5,000 miles per hour. One dust particle or finger print can cause the head of the rocket to put a serious gouge in the road surface. A smoke particle would appear as a "large boulder" - a fingerprint as a "large slab of rock" - a dust particle as a "small hill" - a human hair as a curved "train of cars".

Head End (communications)
Section of cable television distribution system where signals are collected or originated.

Header (communications, computer/microelectronics)
In microelectronics fabrication, the base of a hybrid circuit package, holding the leads. In computer processing, the first record in a file that identifies the file. The name of the file, date of last update and various other status data are stored in the header: in a document or report, as common text printed at the top of every page; in communications, the first part of the message that contains controlling data, such as originating and destination stations, message type and priority level. Also, a term used to define a connector, usually consisting of two rows of gold plated pins on 0.2 inch centers. A header is used with ribbon cables (such as the cables used to connect an internal CD-ROM drive) or to accommodate daughterboards.

Headers are also used as jumper blocks allowing one to select the device address, interrupt level, other options offered by adapter cards.

Header File (computer)
File type used by C programs to assign names to user-defined data types and symbolic constants and to declare prototypes of the functions used in the application. C header files carry the extension H. The term "include file" is often used synonymously.

Header Label (computer)
Record used for file identification that is placed at the beginning of the file.

Head Per Track (computer)
Disk drive that has a read/write head positioned over each track, eliminating the access arm movement from track to track (fixed head disk device).

Head Room (A/V, production)
Space left between the top of the head and the upper screen edge.

Head Switching (computer)
Activation of a particular read/write head over a particular track on a disk.

Heap (computer)
In programming terms, the free memory currently available to load and run programs.

Hearing Aid (A/V, communications)
Instrument used to amplify sounds, particularly the sound of speech. Modern electronic hearing aids are small enough to be worn comfortably and inconspicuously behind the ear, within the ear canal and concha, in the frames of spectacles, or in clothing. Essential components of a hearing aid are: microphone, electronic amplifier, earphone, plastic ear mold which serves to couple energy from the earphone to the eardrum either directly or through plastic tubes. Sometimes a vibrator is held by a spring headband behind the ear and delivers sound by bone conduction.

H054. Heat Sink (computer)
On a printed circuit board, for example, a space or a material that absorbs heat.

H055. Helical Scan (A/V, computer)
Diagonal tracking for video and digital audio tape (DAT) increasing storage capacity over parallel methods. A videotape recording in which the video signal is put on tape in a slanted, diagonal way (contrary to transverse scanning, which goes across the tape). The helical method is used by all video recorders except "quad" video recorders; it is also called slant track recording. This method has several advantages over older linear recording techniques, including higher storage density and longer tape life.

Help (computer/DOS)
DOS Command that displays a list of DOS commands and brief description, or displays help information on specific commands. This command is used when an operator needs a reminder of the syntax for a command.

Help Index (computer)
On-Screen reference material providing assistance with a program or application.

Help Key (computer)
Key that, when pressed, accesses the user to on-screen reference material.

Hertz (Hz) (communications)
Frequency of electrical vibrations (cycles) per second. Abbreviated as "Hz", one Hz is equal to one cycle per second. In 1883, Heinrich Hertz detected electromagnetic waves. In the early 1970's, cycles per second became standardized as "Hertz".



Heterodyne Principle (communications)
Basic principle underlying the operation of a superheterodyne radio, television, or other receiver, wherein two alternating currents that differ in frequency are mixed in a nonlinear device to produce two new frequencies, corresponding to the sum and the difference of the input frequencies. Only the difference frequency is commonly used in a superheterodyne receiver, where it serves as the input to the intermediate-frequency amplifier. This principle permits conversion of a wide range of different input frequencies to a predetermined, lower intermediate-frequency value that can be amplified efficiently. Some frequency meters also use the heterodyne principle when comparing an unknown input frequency with a calibrated frequency standard.

H061. Heuristic (computer)
Method of problem solving using exploration, trial and error methods. Heuristic program design provides a framework for solving the problem in contrast with a fixed set of rules (algorithmic) that cannot vary. (Heuristic, more human - Algorithmic, computer).

Hexadecimal: Hex (computer)
Meaning sixteen, it is the base 16 numbering system used for representing all possible values of a number, character, byte. Each half byte (four bits) is assigned a hexadecimal digit. Hexadecimal is used because of its uniformity. Two hexadecimal digits always make up one byte, (decimal can be 0 through 255) (other systems are binary, decimal, octal).

Hidden Attribute (computer/DOS/Windows)
One of four markers that MS-DOS can use to classify a disk file. Files with the hidden attribute are not ordinarily displayed in File Manager's directory windows, but a user can us the View menu's Include command to make them appear.

Hidden File (computer/DOS)
System file that cannot be viewed, such as the common MS-DOS BIOS file.

Hierarchical (communications, computer)
Hierarchical structure are a one to many relationship, each item having one or more items below it. In communications, a hierarchical network refers to a single computer that has control over all the nodes connected to it.

Hierarchical File System (computer/DOS)
File system that stores data in a top-to-bottom structure requiring that all access to the information start at the top and work down through the levels of hierarchy. In DOS the root directory is the hierarchical start point. Files can be stored in the root directory, or directories can be created off the root directory, that become subdirectories.

Hierarchical Menu (computer/Windows)
A menu with multiple levels. The menu consists of a main menu leading to one or more levels of submenus from which choices of actions are made. Almost all Windows applications use hierarchical menu structures.

High 8: Hi-8 (A/V)
Abbreviation for High Band 8 millimeter, a format developed by Sony Corporation for camcorder videotapes. Hi-8 provides the capability of recording PCM digital audio and time-code tracks in addition to conventional analog audio and enhanced-quality video information. Hi-8 format is found on Sony commercial and industrial equipment and is now beginning to be more commonly used in audio/visual consumer products.

High Angle (A/V, production)
Refers to a shot looking down on the action below.

High Band (A/V, communications)
In A/V equipment it refers to the frequency of the video information. High-band videotape recorders operate on a high frequency range (7 to 10 megahertz FM signal deviation), providing operationally higher quality pictures with less video noise and better resolution than low-band recordings. Most high quality color machines are high-band.

High Bit Characters (computer)
Characters with ANSI or ASCII values higher than 127.

High Definition Television: HDTV (A/V, communications)
Use of special cameras and recording equipment for the production of high-quality pictures. The pictures have a higher resolution (show smaller detail more clearly) than regular television pictures. For example, double the 525 lines of resolution for Broadcast TV (see HDTV).

High Frequency Impedance Measurements (communications)
Electrical measurement of the complex ratio of voltage to current in a given circuit at frequencies from several hundred kilohertz (kHz) to 100,000 megahertz (MHz). this frequency range includes medium and high-frequency bands. The types of measurements include: voltmeter/ammeter; vector impedance meter; potentiometer; series-resonance; parallel-resonance; resonant-rise method; radio frequency bridges; microwave null devices; standing-wave methods; general radio reflectometer; automatic plotter; impedance plotter.

High Hat (A/V, production)
Cylinder-shaped camera mount that can be bolted to scenery or a dolly to permit panning and tilting of the camera without tripod or pedestal.

High Key (A/V, computer/printing)
In audio/visual production, high intensity overall illumination where the background is generally lit. In computer/printing terms, a photograph in which the majority of tonal values are higher, or lighter, than a middle grey.

High Level Data Link Control: HDLC (communications)
Protocol defining standards for linking Data Terminal Equipment, and Data Communications Equipment (part of ISO/OSI standards - see HDLC).

High Level Language
Programming Language using symbols and statements that can be read; problem-oriented language independent of any particular computer on which the program is finally run.

Highlight (computer/printing)
Whitest or brightest parts of a photograph; the opposite of shadow.

Highlight Bar (computer)
Line within an on-screen menu that may be displayed in reverse video or different colour.

H080. Highlighted (computer/Windows)
Indication that an object or text is selected and will be affected by the next user action. It can appear in reverse video on monochrome displays or in colour on colour displays. Highlighted objects might change colour or be surrounded by a selection cursor.

High Polymer Transducer (A/V, communications)
Transducer that uses a piezoelectric high-polymer film, consisting of polyvinylidene fluoride. Of particular interest are high-polymer loudspeakers and high-polymer stereophonic headphones. As the film is very thin and flexible, an omnidirectional high-polymer loudspeaker was developed making the film into a cylindrical shape. The loudspeaker has perfect omnidirectional pattern in the horizontal plane. The high-polymer headphones have wide frequency range, flat frequency response, low distortion, light weight, thin shape, and high stability around moisture and dust.

High Temperature Electronics (communications, computer, microelectronics)
Technology of electronic components capable of operating at high temperatures (above 300 degrees celsius). The need for electronic devices for geothermal well probes, planetary space probes, jet-engine controls, and nuclear power plant instruments is supplying the impetus for advancements in this area. Conventional silicon diodes, transistors, and integrated circuits will not function in this temperature range.

High Resolution (A/V, computer, printer)
High-quality image on a display screen or printed form. The more dots used per square inch, the higher the quality. To display totally realistic images including the shades of human skin requires about 1,000 x 1,000 pixels per square inch on a 15" diagonal screen. Desktop laser printers print respectable text and graphics at 300 dpi.. Typesetter systems print 1,200& 2,400 dpi (and higher).

High Sierra Format (A/V, computer)
Name assigned to the predecessor of ISO standard 9660 defining the table of contents and directory structure of CD-ROMs for computer applications. Microsoft's MSCDEX.DRV driver reads the table of contents and directory structure and converts the latter to the structure used by DOS. This function enables the user to treat CD-ROM files as if they were located on a conventional hard disk drive.

High Speed Shutter (A/V)
Feature on camcorders for recording fast-paced movement with the high speed shutter switch on. While in playback mode or slow mode, a VHS, VCR will show the fine points of any motion at 1/100th, 1/250th, or 1/500th of a second with no blurred screen image. As a cautionary note, this feature increases the LUX level (light level needs) dramatically, so this feature should only be used outside during bright sunlight.

High Temperature Reverse Bias (computer/microelectronics)
Burn-in type test of diodes and transistors conducted with the junctions reverse biased to affect any failure due to ion migration in bonds of dissimilar metals.

Hints (computer/printing)
Algorithms contained in some fonts, such as Adobe PostScript fonts, that increase type quality when printing at low resolutions or in small point sizes.


Hit Rate (computer)
Percentage of time that information being sought or accessed is found in a cache memory.

HLLAPI (communications, computer)
High Level Language Application Program Interface; from IBM that allowed a personal computer application to communicate with a mainframe application. The hardware hookup was handled using a 3270 emulation package. HLLAPI allowed the personal computer program to interact with the mainframe application.

HMI Light: Halogen Metal Iodide (A/V, production)
Extremely efficient, high-intensity light burning at 5,600 degrees Kelvin (outdoor illumination). It needs an additional piece of equipment, a ballast, to operate properly.

HMS Time (A/V, computer)
Time expressed in hours, minutes, and seconds, usually separated by colons.

HMSF Time (A/V, computer)
Time expressed in hours, minutes, seconds, and video or motion picture frame. SMPTE time code and Sony RC time code are examples of HMSF.

Hog (computer)
Term sometimes used to describe a program or application that uses inefficient or excessive amounts of computer memory or other resources.

Holes In Solids (communications/microelectronics)
Vacant electron energy states near the top of an energy band in a solid are called holes. A full band cannot carry electric current; a band nearly full with only a few unoccupied states near its maximum energy can carry current, but the current behaves as though the charge carriers are positively charged. Hole conduction is important in many semiconductors, notably germanium and silicon. The occurrence of hole conduction in semiconductors is favored by alloying with a material of lower valence than the "host". The mobile vacancy or electron deficiency in the valence structure of a semiconductor makes it equivalent to a positive charge.

Hollerith Cards (historic/computer)
Punched card 90 column data processing system using cards that were sized the same as the size of the 1870's dollar currency size; the main reason being that the inventor Herman Hollerith (1860-1929), could store his new punched cards in the same economically priced cabinets and file drawers as standardized for currency. Hollerith had a monopoly on punched cards for 25 years, from 1890 to World War I. Hollerith was the founder of the firm that evolved to become IBM.

Hologram (A/V, photonics)
Recording of interference pattern between an object beam and a reference beam of light. Such a recording allows for the reconstruction of the wave front of the object beam.

Holographic Optical Element (A/V, photonics)
Optical element that is realized by means of a hologram, rather than by traditional (usually refractive) devices.

Hololens (A/V, photonics)
Holographic Lens.

Home Computers
Same industry as personal computers, except for the home and home/office use. It was an early name given to personal computers.

Home Controls (computing)
Term sometimes used to describe computer-controlled devices that provide utility functions in the home (security checks, phone answering features, light switching, temperature monitoring, etc.).

Home Directory (computer/Windows)
Directory that is accessible to the user and contains files and programs for that user. A home directory can be assigned to an individual user or can be shared by many users.

Home Key (computer)
Keyboard key used to move the cursor to the top of the screen or to the previous word or beginning of a line (can be used in conjunction with the arrow keys).

Hook (computer)
Programming term used to describe instructions that provide logical breakpoints for future expansion. Hooks may be changed to call some outside routine or function or may be placed where additional processing is added. The term also sometimes refers to certain attributes between similar operating systems or programs that allow some features to be used, but can disallow other features between competitive programs.

Hopper (computer)
Device (tray, chute, shuttle) that accepts input to a mechanical device for unattended disk duplication, 35mm slide conversions, or other repetitive tasks.

Horizontal Drive (A/V)
Pulse at horizontal rate used in TV cameras. Its leading edge is coincident with the leading edge of the horizontal blanking pulse, and the trailing edge is coincident with the trailing edge of the horizontal sync pulse.

Horizontal Plane (A/V, production)
Lines parallel to the horizon in a picture. The horizontal plane should be kept level unless a special effect is intended.

Horizontal Resolution (A/V)
Number of vertical lines observed by a video camera or receiver in a horizontal direction on a television test chart. A rating for detail quality in a monitor/receiver or Television picture. The more lines, the better. A standard VHS, VCR records and plays back approximately 160 to 240 lines of horizontal luminance resolution. A High 8, or S-VHS, or laser disc player plays back approximately 330 lines of horizontal resolution.

Horizontal Sync (A/V)
Sync pulses that control the horizontal scanning of the electron beam at 15,734 Hz for colour and 15,750 Hz for black and white.

Host (communications, computer)
Controlling computer in a timesharing or distributed processing environment.

Host System (communications, computer)
In multiprogramming systems, the host system is responsible for allocating storage and I/O (input-output) resources to each of the logical machines (active programs) which are usually called virtual machines - as they are required. This allows a number of virtual machines to share physical resources without logical conflict. In microcomputer systems, the notion of host system applied to the physical machine that interprets (emulates) the programs written in other machine languages. The machine being emulated by the host machine is said be the image machine. Another and an increasing use of the term host system is in time-sharing or remote computing, where the host is the central computer providing service to terminals or satellite computers (host computer vs remote computer).

Hot (A/V, production)
Current or signal-carrying wire. Also, instruments that are turned on, such as a hot camera, or a hot microphone, or a hot amplification system.

Hot Editing (A/V, production)
Method of assembling shots when producing a completely edited tape during production. The editor stops the videotape from time to time to correct mistakes or to change the set or costumes and proceeds by editing the next take directly onto the existing master tape.

Hotkey (computer)
Selected key or combination of keystrokes that can cause an automated function or series of functions to occur no matter what else is occurring at the time. Hotkeys are commonly used to activate memory resident functions (such as TSR's - terminate, stay resident).

Hot Link (computer)
Term describing a dynamic data exchange (DDE) operation in which a change in the source of the DDE data (the server) is immediately reflected in the object of the destination application (the client) to which it is linked.

Hot Spot (A/V, production)
Undesirable concentration of light in one spot; it can be especially noticeable in the middle of a rear screen projection image.

Housekeeping (computer)
Set of instructions that can be executed at the beginning of a program to set conditions, set all counters and flags to their starting values and prepare a program for executions. The term can also include day-to-day maintenance chores on computer hardware, software, or application functions.

House Number (A/V, production)
In-house system of identification; each piece of a recorded program must be identified by a certain code number, called house number, since they differ from station to station (house to house).

HPGL (computer/printer)
Hewlett-Packard Graphics Language - designed for use with Hewlett-Packard plotters, it is a vector format for graphic images.

HPIB (computer)
Hewlett-Packard Interface Bus - version of the IEEE 488 General Purpose Interface Bus.

HPPCL (computer/printer)
Hewlett-Packard Printer Control Language. HPPCL was designed to create and manipulate images to be printed by HP LaserJet printers. Several numbered versions of HPPCL implemented by specific LaserJet models exist.

H Rate (A/V)
Time that it takes for scanning one complete horizontal line, including trace and retrace.

HSG (A/V, computer)
High Sierra Group abbreviation - HSG indicates the directory format of a CD-ROM in High Sierra format rather than ISO-9660 format.

Hue (A/V, production)
Attribute of colour perception that determines whether the colour is red, green, blue, etc.

Hum (A/V, communications, computer)

Unwanted signal, usually in an audio input circuit, from power lines or electromagnetic fields. Hum in the U.S.A. is 60-Hz. In most other regions of the world, hum is 50-Hz. It is minimised by proper shielding and grounding of audio and video components.

Hybrid Circuit (computer, microelectronics)
Making integrated circuits using a combination of monolithic, thin-film and thick-film techniques.

Hybrid Computers (communications, computer)
Systems with at least one stored-program digital processor linked with a multiplicity of analog counting units, have been used since the late 1950s for the solution of a wide range of engineering simulation studies. In addition, the continuous parallel computing capability of analog devices in combination with the sampling and storage facilities of the digital computer, has proven to be very efficient for complex signal processing.

Hybrid Microcircuit (computer/microelectronics)
Circuit composed of different types of integrated circuits and discrete components, mounted on a ceramic base, especially suited for customised analog functions.

Hybrid Network (communications)
Network made up of equipment from different manufacturers, communicating compatibly.

Hypercube (computer)
Parallel processing architecture containing binary multiples of computers (4, 18, 16, 32, 64, 128, 256, 512, 1024); all interconnected so that data travel is kept to a minimum and maximizes individual processing power of each connected computer for the whole result.

Hysteresis (communications, computer)
Lag between making a change, such as increasing or decreasing power or signal strength, and the response or effect of that change.