hacker
Someone who has the computer and network expertise to access information that others have tried to make inaccessible to anyone but those whom they have chosen. Some hacks steal or modify information. A different breed of hacker creates viruses. Hackers are the anti-heroes of the internet. See also netizen.
halftone
An image consisting of tiny dots. If you take a magnifying glass to a newspaper photo, the dots become obvious.
hard disk
A medium used for storage of computer data. This is long term or permanent memory as opposed to the transient working memory of RAM since the latter must be supplied with power to retain its contents whereas the former does not. Like audio tape, a hard disk is typically a material embedded with metal particles such as iron oxide. The disk is spun around and is interpreted with a reading and writing head which floats a microscopic distance above the disk. The disk is hard and rigid so the head does not touch the surface, thus allowing speeds greater than floppy disks, i.e. 3600 rpm versus 300 rpm. Hard disks typically have a 8-10 ms seek time and transfer rates at ATA or SCSI speeds, i.e. 5-160 Mb/s. See also removable storage.
hard page fault
See page fault.
hardware
The physical components of a computer. This includes the system unit, the front-end, and the backend. The hardware is the first level of a computer, the second is the software.
Harvest
A search engine that can work with WWW client/server applications like HTTP, FTP, NNTP, and Gopher.
HDTV
High Definition TeleVision. Television standards that uses digital instead of analog data. The HDTV screen is wider than regular TV, ie it has an aspect ratio of 16 wide by 9 high instead of 4 wide by 3 high. HDTV has a higher resolution, ie 1080 lines per screen as opposed to 525. Depending on screen size this can look like 35 mm film. The data can also be compressed for transmission and decompressed for viewing. This should help merge the television with the computer. Currently computer displays use RGB standards which are incompatible with the standards for TV. The FCC plans to have HDTV phase in by 2006. See also TV.
Aka header. The part of a document that contains preliminary information only. The head should not contain any document content which should be found in the body. Usually the entire head is examined before the body is looked at.
heap
Processing memory that can hold a variable size of data. The size and data type is determined at execution. See also stack.
Hello world!
Traditionally some programming variation of Hello world! is first when being introduced to a new programming language.
Relating to a numbering system with a base of 16. The digits usable are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A=10, B=11, C=12, D=13, E=14, and F=15, just as in a decimal system where the largest digit usable is 9. Each digit in a hexadecimal number is 16 to the power of the digit's position, with the first position being the power of zero.

The following may or may not be helpful in explaining a octal numbering system:
• Hexadecimal counts as follows: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, 10, 11,.... For comparison, decimal counts as follows: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,....
• Binary number may occur in quartets (sets of four). The positions of the octet may be numbered (from left to right) 3, 2, 1,and 0. The maximum in each position is 16 to that power. The value of each digit in each position would be 16^3=4096, 16^2=256, 16^1=16, and 16^0=1. For comparison, for a quartet of decimal numbers, the value of each digit in each position would be 10^3=1000, 10^2=100, 10^1=10, and 10^0=1.
• From right to left a binary system has a ones place, a 16s place, a 256s place, a 4096s place, a 65536s place, etc. For comparison, from right to left a decimal system has a ones place, a tens place, a hundreds place, a thousands place, a ten thousands place, etc.
• Given an arbitrary octal number FA8, its decimal equivalent is 15*16^2 + 10*16^1 + 8*16^0 = 3840 + 160 + 8 = 4008. For comparison, the decimal number 170 = 1*10^2 + 7*10^1 + 0*10^0 = 100 + 70 + 0.
Hexadecimal is often used to express binary in a compressed fashion. EG: Ethernet addresses are 48 bits or 6 octets: this can be expressed as 6 2-digit hex numbers or 3 4-digit hex numbers.

Hexadecimal is also used to code things. EG: gold=#FFD700.

The c/c++/java shorthand for a hexadecimal value is to prefix with 0x. EG: This decimal value int y = 12 is the same as this hexadecimal value int y = 0x2C.

hierarchal database
A collection of information in parent-to-child relationships from top to bottom. EG: Animals: Mammals: Canines: Dogs. The relationships may be one-to-one or one-to-many.
High Definition Television
See HDTV.
high-level language
A programming language that reads more closely to everyday English. These are also called symbolic programming languages in that the English-like language is symbolic of low-level machine language. These programs must either be compiled by a compiler into executable machine language, or interpreted by an interpreter which then executes the program line by line. See programming languages.
host
Any machine with a network interface configured to use TCP/IP, , eg a user's host name may be Sue and her domain may be Marketing.
hot swappable
Devices such as hard drives, floppy drives, and PC cards that can be removed and replaced without turning the computer off.
hop
The connection between two network devices, regardless of the route it takes to get there. As far as the Internet is concerned, the hops are usually counted as being between routers.
HPC
Handheld Personal Computer.
hqx
.hqx. Mac files that have been converted between ASCII and binary with the BinHex encoding process. It preserves the file type, icon, and full Mac name.
HSL
Hue Saturation Lightness.
HtGrep
A PERL script that can be used as a CGI accessed search engine for a web site.
HTH
Hope This Helps.
HTML
HyperText Markup Language. HTML is RFC 1866, the programming language of the WWW. HTML 0.0 was developed by Berners-Lee in 1990. An HTML document on a web server presents information with text or objects that can lead to other information via URLs. It is a specific application of SGML in the WWW. Different versions of HTML are different DTDs of SGML. XML is somewhere between SGML and HTML.
HTTP
Hyper Text Transfer Protocol. Used since 1990, HTTP is client server protocol that allows the user's browser to download and interact with HTML pages on an Web server. It exists at the Application Level of the OSI Reference Model. HTTP is considered stateless since it cannot maintain application information from session to session.
HTTPd
Hyper Text Transfer Protocol Daemon. The software that a web server uses to monitor its Internet or intranet connection for requests from clients.

Here are some of the more popular HTTPd packages available:
HTTP server
A file server that specializes in HTTP for distributing HTML pages. A typical user uses his or her browser to connect to an HTTP server at the default TCP port of 80. Then the server processes the request, returns a response, and then disconnects. That leaves the HTTP server free to service other users. Of course during a typical session a user will often connect to a multitude of different HTTP servers all over the world.

netstat is a common TCP/IP utility used to monitor HTTP sessions.
HTTP Status Codes
A three-digit number indicating the status of an HTTP server. These are common codes:
1xx Informational (reserved)
2xx Success
204 No Response
3xx Redirection: needs more action to complete
301 Document Moved
4xx Client Error: request had incorrect syntax
401 Unauthorized
403 Forbidden
5xx Server Error
501 Not Implemented
A complete listing of HTTP Status Codes can be found at http://www.w3.org/Protocols/HTTP/HTRESP.html
HTX
HyperText markup language eXtension. Used by IDC to format the results of a SQL query submitted from a web page. This is legacy technology since the introduction of active server pages. See also IDC.
hub
(1) Aka concentrator or multiport repeater. A hub connects multiple network segments in a star topology and usually operates in the OSI Physical Layer. Each network segment is connected to a port on the hub. There are three kinds of hubs:
• A passive hub merely connect network segments. It takes a signal from each port and retransmits it to the other ports with out boosting the signal.
• An active hub is like a passive hub that also act as a repeater, i.e. it takes a signal from each port, cleans it up, and boosts the signal before passing it on to the other ports.
• An intelligent or switched hub is an active hub that may perform additional services such as packet switching, traffic routing, and traffic monitoring.
(2) A common non-Ethernet hub is a USB hub. A USB hub connects multiple USB devices to a computer.

hue
Aka chroma. A point on the color spectrum, independent of value and saturation, eg red v. green.
hunt group
In phone mail systems, the outside world can call one of your numbers. The call is forwarded to an extension in that number's hunt group. After a certain number of rings, the call is forwarded to another extension. This continues n number of times. If no one in the hunt group answers by the last extension, then the number goes to a voice mail extension. EG:
• A customer dials 312-555-7500.
• The call rings at x4000.
• If no one answers after 4 rings, it then rings at x4001.
• If no one answers after 4 rings, it then rings at x4002.
• If no one answers after 4 rings, it then goes to voice mail at x4100.
HW
HardWare. The part of a computer system that can be kicked.
hypertext
A word coined in 1965. It refers to the concept of information being linked directly to other related information. Medias other than just text are now hyper. Apple came utilized hypertext or hypermedia technology with HyperCard in 1987 but never realized its potential.
Hyper Text Markup Language
See HTML.
Hyper Text Markup Language Extension
See HTX.
Hyper Text Transfer Protocol
See HTTP.

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