H.261, H.263, etc. — see H.x series

H2GF (HiperLAN2 Global Forum)
A consortium created to promote the European Telecommunications Standards Institute's (ETSI's) High-Performance Radio LAN Type 2 (HIPERLAN/2) standard. (Unlike the ETSI, H2GF styles the standard's name as "HiperLAN2.") See HIPERLAN/2.

HA (see high availability)

HA-API (Human Authentication Application Programming Interface)
A biometric interface specification originally developed at the request of the U.S. Department of Defense. In 1999, the HA-API working group merged with the BioAPI Consortium, and HA-API was merged with I/O Software's Biometric Application Programming Interface (BAPI) into the consortium's BioAPI specification. See BAPI and BioAPI.

HACMP (High Availability Clustered Multiprocessing)
An IBM RS/6000 product designed to provide a high-availability configuration by enabling automated failover from one RS/6000 to another.

half duplex
A circuit designed to handle two-way transmission by transmitting alternately in each direction, but not in both directions simultaneously. See full duplex.

hand geometry
The shape and features of a person's hand, as used in biometric technology to authenticate identity.

Handheld Device Markup Language (see HDML)

handling unit
A unit of goods, as viewed from the perspective of how goods are handled for distribution and logistics purposes. Examples include all the goods contained in carton or bundled on a pallet, or all the goods transferred in a single shipping container, rail car or truck trailer.

handset
A piece of handheld, end-user telephony equipment that contains a transmitter, receiver and keypad for dialing phone numbers. Cell phones, for example, are often referred to as "wireless handsets."

handshake
The exchange of predetermined control signals when a connection is established between modems or other communicating devices.

handwriting recognition
Technology that performs pattern matching to convert handwritten letters into computer-recognizable text characters. The two subfields are static recognition of handwritten documents such as forms, and dynamic recognition of real-time handwriting for devices such as personal digital assistants.

HARC (Hitachi Asynchronous Remote Copy)
A remote copy function for Hitachi Data Systems storage products. HARC allows movement of large amounts of data over any distance with full data integrity and minimal impact on performance. It duplicates data files directly from a primary subsystem to a secondary one without using valuable server processor cycles.

hard disk
The main data storage area of a computing device. The hard disk is typically where the computer's operating system and other software are permanently stored. Hard disks have a larger storage capacity and faster data retrieval capabilities than floppy disks.

hard drive (see HDD)

hardware
Machinery and equipment associated with computing devices. A computer is composed of both hardware and software. The software provides the instructions, and the hardware performs the processing.

hardware description language (see HDL)

hardware RAID
A redundant array of independent disks (RAID) storage solution that uses a processor separate from the application processor, and that provides nonvolatile memory for the data and instructions it receives from the host system. The term "hardware RAID" generally implies a dedicated disk array controller board — with its own microprocessor, memory and microcode — that implements the RAID functions and computations. However, the concept can be extended to storage servers that perform RAID operations using standard computer hardware and operating-system software. See RAID.

hardware token
A small device used to authenticate user access to an information system. Hardware tokens are distinguished from smart cards in that they do not require any type of reader or sensor. They are synchronized with an authentication server at the time they are issued, and they remain synchronized with the server for the life of the token. The token generates and displays a one-time password, which the user types into the device he or she uses to access the system, along with his or her personal identification number. The principal advantage of hardware tokens is their portability. They enable authentication from any device without imposing any special software or hardware requirements on the device. The principal disadvantage is the requirement that users carry the tokens with them, although credit-card-size tokens and key-fob form factors reduce the nuisance factor of this burden.

hard-wired
Having a permanent electronic configuration or connection. The term generally refers to electronic circuitry that performs fixed logical operations by virtue of unalterable circuit layout, rather than under computer or stored-program control. However, it can also be used to describe a communications link that permanently connects two nodes, stations or devices.

hashing
An algorithm that generates a unique "checksum" based on the content of transaction data, so that it can be verified by recipients using the same algorithm in reverse to ensure the content was not modified.

HBA (host bus adapter)
An adapter used to connects a host computer to a storage network.

HBT (heterojunction bipolar transistor)
A high-speed transistor design used in some semiconductors.

HCFA (Health Care Financing Administration)
A U.S. federal agency created in 1977 to coordinate the nation's Medicare and Medicaid programs. In 2001, HCFA was renamed the Centers for Medicare & Medicaid Services.

HCFA-1500
A uniform billing scheme widely used by healthcare payers for purposes of reimbursement and historical documentation. The name refers to the billing form for which the scheme was devised by U.S. Health Care Financing Administration (HCFA), now known as the Centers for Medicare and Medicaid Services.

HCM (human capital management)
A set of human-resource practices that focus on acquisition, management and optimization of the enterprise workforce.

HCO (healthcare organization)
A general term covering a variety of enterprises that use healthcare information systems. HCOs include care delivery organizations (CDOs) such as hospitals and physician practices, as well as healthcare payer organizations such as health plans. See CDO.

HDA (head disk assembly)
A sealed storage assembly containing disks, a magnetic head and access arms. By reducing contamination, a sealed HDA enables the head to fly closer to the disk surface, increasing the areal density that can be obtained.

HDD (hard disk drive)
A computer component (also called a "hard drive" or "rigid disk drive") that contains a hard disk, along with the magnetic head and drive mechanism used to store and read data from it. Unlike a floppy disk, the disk in an HDD is not removable. See floppy disk and hard disk.

HDL (hardware description language)
A programming language used by electronics engineers to design hardware components or devices, such as processors, cell phones or computers.

HDLC (High-Level Data Link Control)
A bit-oriented data link protocol developed by the International Organization for Standardization (ISO). One of the most commonly used protocols in the data link layer (Layer 2) of the ISO's Open Systems Interconnection (OSI) reference platform, HDLC adds data link control information to a transmitted frame of data. Variations of HDLC are used in X.25 and frame relay networks. See OSI, frame relay and X.25.

HDML (Handheld Device Markup Language)
A device- and network-independent application language developed by Unwired Planet for Web programming on a handheld device with limited memory and display, such as a cellular phone or an organizer.

HDS (Hitachi Data Systems)
A vendor of enterprise and modular storage systems and software. HDS is a wholly owned subsidiary of Tokyo-based electronics firm Hitachi, Ltd.

HDSL (high-bit-rate digital subscriber line)
One of several digital subscriber line (DSL) technologies. HDSL (also known as "high-speed digital subscriber line") provides network or Internet access over voice lines at 1.5 megabits per second. See DSL.

HDTV (high-definition television)
A high-resolution, wide-screen video format. HDTV images contain roughly twice the number of vertical and horizontal lines compared to conventional television images.

head disk assembly (see HDA)

head end
The originating point in a one-to-many network system (such as a TV cable network), or a central information-gathering point of an Internet service provider.

header
The initial portion of a network packet or e-mail message. The header contains any information and control codes that are not part of the message itself (such as routine or priority status, message type, destination, sender and time of origination).

head-mounted display (see HMD)

Health Care Financing Administration (see HCFA)

Healthcare Information and Management Systems Society (see HIMSS)

healthcare information system (see HIS)

healthcare organization (see HCO)

Health Insurance Portability and Accountability Act (see HIPAA)

Health Level Seven (see HL7)

health maintenance organization (see HMO)

Health Plan Employer Data and Information Set (see HEDIS)

HEDIS (Health Plan Employer Data and Information Set)
A set of standardized performance measures designed to provide purchasers and consumers with the information they need to reliably compare healthcare organizations' performance. HEDIS 99 contains measures that cover disease prevention and acute or chronic care across a full range of healthcare settings, such as physicians' offices, clinics and hospitals.

helical scan
A recording method used to increase data capacity and transfer rates in tape storage. The tape is wrapped around a transport drum at an angle, creating diagonal tracks that increase track density compared to conventional tape-recording methods.

help desk
The first point of contact for all technical and end-user support issues. Most help desks offer at least two tiers of support. Tier 1 is where routine or simple problems are solved, and where more-complex ones are handed off to a higher tier. Tier 2 help desk analysts have more in-depth technical knowledge or specialized expertise.

help system
A consistent, system-supplied mechanism for system and application programs to offer context-sensitive help to end users.

HEP (horizontal enterprise portal)
A portal that serves a broad population of users across an enterprise — unlike a vertical enterprise portal (VEP), which serves only a specific segment of this population. See portal and VEP.

hertz (see Hz)

heterogeneous
Applied to IT, this term describes a system, network, architecture or application portfolio that contains a variety of disparate components (such as hardware, operating systems, middleware, applications or network protocols), typically from multiple vendors.

heterojunction bipolar transistor (see HBT)

Hewlett-Packard (see HP)

hexadecimal
A number system based on 16 digits. Hexadecimal notation — with the numbers 0 through 9 representing the first 10 digits, and the letters A through F representing the final six — is typically used in storage or memory addressing to identify each of 16 possible bit patterns.

HF (see high frequency)

HFC (hybrid fiber coaxial)
A network architecture that consists of fiber in the backbone network and coaxial cable in the access network. HFC can be used to provide high-speed network service to the home for applications such as video.

hierarchical database
A database that is organized in a tree structure in which each record has one owner. Navigation to individual records takes place through predetermined access paths.

hierarchical storage management (see HSM)

high availability
A high probability that a system will be operational at any given time, and will recover quickly in the event of a failure. In general, a high-availability system has a relatively low vulnerability to unscheduled outages, such as power failures, code defects or hardware failures.

High Availability Cluster Multiprocessing (see HACMP)

high-bit-rate digital subscriber line (see HDSL)

high-definition television (see HDTV)

high frequency
The portion of the electromagnetic spectrum typically used in short-wave radio applications. It includes frequencies spanning the three- to 30-megahertz range.

High-Level Data Link Control (see HDLC)

high-level language (see HLL)

High-Level Language Application Program Interface (see HLLAPI)

high-performance computing (see HPC)

High-Performance Links (see HiPerLinks)

High-Performance Parallel Interface (see HIPPI)

High-Performance Radio LAN Type 1 (see HIPERLAN/1)

High-Performance Radio LAN Type 2 (see HIPERLAN/2)

High Performance Transaction System (see HPTS)

high-speed circuit switched data (see HSCSD)

high-speed digital subscriber line (see HDSL)

High-Speed Serial Interface (see HSSI)

high-speed subscriber data line (see HSDL)

HIMSS (Healthcare Information and Management Systems Society)
An industry association that offers a variety of publications, educational programs and services related to healthcare information systems. Its members contribute to the development of such technologies as telemedicine, computer-based patient records, community health information networks and portable/wireless healthcare computing.

HIPAA (Health Insurance Portability and Accountability Act)
An act passed by the U.S. congress in August 1996. HIPAA's directives call for the use of electronic data interchange (EDI) in healthcare transactions, and for protecting the privacy of patient healthcare information. Under the HIPAA directives, healthcare organizations (HCOs) face fines of up to $250,000 and 10 years imprisonment for wrongfully disclosing patient information. They also risk having claims rejected if they do not conform to the EDI requirements. The HIPAA directives — for EDI in particular — have major IT implications for HCOs, many of which have devoted considerable time and resources to system compliance efforts.

HIPERLAN/1 (High-Performance Radio LAN Type 1)
A wireless-LAN standard from the European Telecommunications Standards Institute. HIPERLAN/1 is designed to provide high-speed communications (20 Mbps) between portable devices broadcasting in the 5-gigahertz radio band. It is intended to allow flexible data networks to be created without the need for a wired infrastructure. It can also be used as an extension of a wired LAN.

HIPERLAN/2 (High-Performance Radio LAN Type 2)
A 5-gigahertz wireless-LAN standard, developed by European Telecommunications Standards Institute as follow-up to the HIPERLAN/1 standard it introduced in the 1990s. HIPERLAN/2, which provides access at speeds up to 54 Mbps at physical layer, competes directly with IEEE's 802.11a standard, which also operates at 5 gigahertz.

HiperLAN2 Global Forum (see H2GF)

HiPerLinks (High-Performance Links)
A high-speed coupling-link technology introduced by IBM in 1997 for its S/390 mainframes.

HIPPI (High-Performance Parallel Interface)
An American National Standards Institute standard for high-speed channels used in processing-intensive systems, such as supercomputers.

HIS (healthcare information system)
A system or application used to manage hospital or other healthcare-related operations (such as financial, registration, scheduling and back-office functions); also called a "hospital information system."

hit
An individual visit to a Web site or Web page, expressed as a measure of its popularity (i.e., Web traffic volume). For example, a site that had 48,000 visitors during a 24-hour period might be said to have averaged 2,000 "hits" per hour during that period.

Hitachi Asynchronous Remote Copy (see HARC)

Hitachi Data Systems (see HDS)

Hitachi Extended Remote Copy (see HXRC)

Hitachi Remote Copy (see HRC)

HL7 (Health Level Seven)
A set of application-level standards for community health information network (CHIN) initiatives, widely used in hospitals. See CHIN.

HLL (high-level language)
A procedural programming language that offers a higher level of abstraction than assembly language. Examples of HLLs include COBOL, FORTRAN and C. The term is interchangeable with "third-generation language" (see 3GL).

HLLAPI (High-Level Language Application Programming Interface)
An IBM "screen scraping" standard that enables mainframe applications to be accessed using a PC.

HMD (head-mounted display)
A display mounted close to the eye on a headset or goggles, typically using optical techniques to create the illusion of a larger screen further away from the eye. Many HCDs use a small, usually low-resolution liquid crystal display (LCD), and are used for applications such as industrial inspection and maintenance. The 3-D HCDs used in immersive virtual-reality systems are typically based on dual LCDs with a distinct image for each eye (offset to provide depth perception), updated at 30 frames per second.

HMI (human-machine interface)
The control interface used by the human operator of a mechanical or electronic system or device (such as cell phone or factory system).

HMO (health maintenance organization)
An organization that provides prepaid subscribers with a range of healthcare services from a limited group of medical professionals and facilities.

HOLAP (hybrid online analytical processing)
A means of combining data from relational online analytical processing (ROLAP) and multidimensional database (MDDB) sources through the same application. See MDDB and ROLAP.

holding time

1. The amount of time callers spend on hold (for example, when placing a call to a help desk or call center). Also called "hold time."

2. The length of time a communications channel is in use for each transmission. It includes message time and operating time. Also called "connect time."

home page
A Web page that serves as a starting point for access to other pages. For example, a Web site's home page is the one designed to serve as the top-level page or entry point for site visitors. A user's home page is the one specified in his or her browser to be loaded whenever the browser is launched.

HomeRF
A 2.4-gigahertz wireless LAN technology based on a frequency-hopping modulation scheme. HomeRF is designed to transport voice, video and data at an attractive price for consumer purchases.

homogeneous
Applied to IT, this term describes a system, architecture, application portfolio or network that is made up of highly similar or complementary components (such as hardware, operating systems, middleware, applications or network protocols) — often from a single vendor.

hop count
The number of stops a network packet makes from source to destination.

hospital information system (see HIS)

host
The primary or controlling system in a multiple-computer network operation. Typically, the term specifically denotes a network-connected computer that hosts services, facilities or applications used by the other computers or terminals on the same network. For example, a Web host is a computer on which a Web site's pages are stored.

host bus adapter (see HBA)

hosting
Storing data on a server for later access. Typically, the hosting server provides services and tools that expedite access by individuals or other servers. The popularity of the Web has given rise to an industry of hosting services that store Web site pages and provide related services (see Web hosting).

host interface
The link between a network or dedicated communications link and a host computer.

host processor
A mainframe attached to a network for network users' access.

hot standby
Alternate equipment ready to take over an operation quickly if the equipment on which the operation is being performed fails.

hot swap
Replacement of a component or module in a computer or network device while it is still running, rather than shutting it down first.

hot-swappable
Able to be exchanged via hot swaps. See hot swap.

HP (Hewlett-Packard)
A company founded in 1939 in Palo Alto, California, by Stanford University classmates William Hewlett and David Packard. It originally made audio oscillators and grew to become a multibillion-dollar computer vendor. HP acquired Compaq Computer in 2002.

HPC (high-performance computing)
Computing applications that require — or computers that provide — much higher performance (in processing power, memory, etc.) than that provided by most computers in mainstream commercial use. Computers with HPC capability are often called "supercomputers." HPC is typically applied to problems or applications that involve complex or high-speed computations and vast amounts of data — for example, aerospace engineering, artificial intelligence, atmospheric research, cryptographic analysis and experimental physics. See supercomputer.

HPNA (Home Phoneline Networking Alliance)

An alliance to advance technologies for high-speed local-area networking over conventional phone wires. It was founded in 1998 by 3Com, Advanced Micro Devices, AT&T Wireless Services, Compaq Computer, Conexant Systems, Hewlett-Packard, IBM, Intel, Lucent Technologies and Tut Systems.

HPTS (High Performance Transaction System)
A check-processing system from Check Solutions (Memphis, Tennessee).

HP-UX
Hewlett-Packard's Unix implementation, based on the System V operating system with real-time extensions added. See System V.

HR (human resources)
The enterprise function or organization responsible for staffing and personnel issues, such as hiring, employment policies and benefits.

HRC (Hitachi Remote Copy)
A controller-based remote-copy capability used in Hitachi Data Systems storage products.

HR disintermediation
A situation where managers bypass the human resources (HR) organization to define and implement their own technologies and practices to support human capital management (HCM). When no clear enterprise HCM strategy is in place, managers often formulate their own departmental plans and adopt the technologies they feel they need to support individual and group responsibilities for enterprise performance.

HRMS (human resource management system)
Business applications for the management of human resource (HR) transactions, best practices and enterprise reporting. Functions typically include core HR tracking, payroll and benefits. The scope is often extended to include recruiting, competency management, training, time management, performance management and self-service offerings.

HRMS (Human Resource Management System)
A PeopleSoft product.

HSCSD (high-speed circuit switched data)
A Global System for Mobile Communications (GSM) bearer service, already deployed in some networks (notably in Scandinavia, the United Kingdom and Hong Kong). It provides circuit-switched connections at speeds of up to 56 Kbps. This is achieved by channel-bonding time slots to obtain the requested speed. Typically, users will be allowed between two and four time slots in a real-life network. See GSM.

HSDL (high-speed subscriber data line)
A variety of digital subscriber line (DSL) technology that enables data to be transmitted at high speeds (up to two megabits per second) over local phone lines. HDSL provides full-duplex transmission over ordinary copper twisted pairs in unshielded cable. See DSL and full duplex.

HSM (hierarchical storage management)
A storage management technology that can be used to identify inactive data and move it to near-line storage, automate the retrieval process, and migrate the data back to the primary storage medium and provide access for the user.

HSSI (High-Speed Serial Interface)
Standard for a serial interface used to connect to T3 lines (see T3). HSSI operates over a shielded cable at speeds of up to 52 megabits per second (Mbps) and distances of up to 50 feet. Functionally, it serves the same purpose as lower-speed serial interfaces such as V.35 and RS-232, in that it provides the interface for wide-area-network communications (see V.35 and RS-232).

HTML (Hypertext Markup Language)
A document-formatting language derived from the Standard Generalized Markup Language (SGML), predominately used to create Web pages. The user's browser interprets HTML commands and formats the page layout, fonts and graphics on the screen. One of the more powerful features of HTML is its ability to create hyperlinks that enable the user to navigate between documents and files with a single click. HTTP is also sometimes used for messaging attachments as a way of supporting rich text formatting across product boundaries.

HTTP (Hypertext Transport Protocol)
The Internet standard for accessing and exchanging documents on the Web. It is a client/server protocol used to connect to Web servers.

HTTPS (Secure Hypertext Transport Protocol) — see S-HTTP

hub
A central device, usually in a star topology local-area network, to which each station's wiring is attached; also called a wiring concentrator. See intelligent hub.

human-machine interface (see HMI)

human resources (see HR)

HVP (healthcare vertical portal)
An Internet-based vendor that provides a foundation for creating e-business and e-health functions in conjunction with a care delivery organization by providing one or more of the following:

• Organized access to focused aggregate healthcare content

• Connectivity solutions for linking business partners and healthcare stakeholders

• E-commerce functions for managing business transactions

• Linkages to improve supply chain management operations by using the Internet as the communication and transaction medium

HW (see hardware)

HXRC (Hitachi Extended Remote Copy)
A remote-copy function for Hitachi Data Systems storage products. HXRC uses an asynchronous copy approach to deliver high data integrity with minimal disruption and performance impact to the primary system. It is compatible with industry-standard Extended Remote Copy (XRC). See XRC.

H.x series
A series of computing standards from the International Telecommunication Union (ITU). It includes:

• H.261: A standard for video compression (also known as px64). H.261 is a worldwide standard and therefore must accommodate both the North American National Television System Committee (NTSC) and European Phase Alternate Line (PAL) protocols. See PAL and NTSC.

• H.263: The video component of the H.323 videoconferencing suite.

• H.263+: A standard for compression of video at 128 Kbps.

• H.320: An international "umbrella" standard for audioconferencing and videoconferencing. It comprises many related standards, including H.261.

• H.323: An umbrella standard for audioconferencing and videoconferencing. It is a videoconferencing suite that has G.723 voice, T.120 collaborative and H.263 video components in a single session.

• H.324: An international standard for videoconferencing over the public switched telephone network.

hybrid card
A smart card that supports both contact-based (e.g., magnetic stripe) and contactless reader technologies. See smart card and contactless card.

hybrid fiber coaxial (see HFC)

hyperlink
An area on a Web page that, when clicked on with a mouse, will transport the user to another Web page. Also called "links" or "hot links," hyperlinks are analogous to hypertext. Hyperlinks are commonly used on the Web to provide navigation, reference and depth where published text cannot. A hyperlink can be created from text or from a graphic.

hypertext
Text that uses links to provide navigation among Web pages or documents. When the text is "clicked on," it can enable a user to navigate within or between Web pages. See hyperlink.

Hypertext Markup Language (see HTML)

Hypertext Transport Protocol (see HTTP)

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