<World-Wide Web> The {World-Wide Web} {search engine} that
	indexes the greatest number of web pages - over two billion by
	December 2001 and provides a free service that searches this
	index in less than a second.

	The site's name is apparently derived from "{googol}", but
	note the difference in spelling.

	The "Google" spelling is also used in "The Hitchhikers Guide
	to the Galaxy" by Douglas Adams, in which one of Deep
	Thought's designers asks, "And are you not," said Fook,
	leaning anxiously foward, "a greater analyst than the
	Googleplex Star Thinker in the Seventh Galaxy of Light and
	Ingenuity which can calculate the trajectory of every single
	dust particle throughout a five-week Dangrabad Beta sand
	blizzard?"

	{Home (http://www.google.com/)}.

	(2001-12-28)

1. <hardware> A generic term for a {display device} that shows
	text and/or images on a roughly flat rectangular surface.  The
	most common type is usually refered to as a "{monitor}" and is
	based on a {cathode-ray tube}, though {flat panel} displays
	have, since around 2000, become increasingly competitive in
	price and performance.

	(2005-07-28)

	2. A {screen multiplexer} utility which lets you run multiple
	{interactive} {terminal sessions} (and {curses} programs)
	through a single terminal connection (on one {virtual
	console}, one terminal, through one {modem} link, {telnet}
	session or {xterm}).

	Screen can detach processes from one terminal and attach them
	to another.  "Auto-detach" lets you continue working after
	being disconnected and reconnected.  It supports keyboard
	driven cut and paste from any text and/or curses application
	(like {Lynx}) to any other (like {xemacs}).

	Screen comes with many {Linux} distributions and is available
	(free) on many other {Unix} {platforms}.

	(2005-07-29)

<communications> Any part of a signal that is not the true or
	original signal but is introduced by the communication
	mechanism.

	A common example would be an electrical signal travelling down
	a wire to which noise is added by inductive and capacitive
	coupling with other nearby signals (this kind of noise is
	known as "{crosstalk}").

	A less obvious form of noise is {quantisation} noise, such as
	the error between the true colour of a point in a scene in the
	real world and its representation as a {pixel} in a digital
	image.

	(2003-07-05)

<programming> (Or "computer program", "program", "code") The
	instructions executed by a computer, as opposed to the
	physical device on which they run (the "{hardware}").

	The term was coined by the eminent statistician, {John Tukey}.

	Programs stored on {non-volatile storage} built from
	{integrated circuits} (e.g. {ROM} or {PROM}) are usually
	called {firmware}.

	Software can be split into two main types - {system software}
	and application software or {application programs}.  System
	software is any software required to support the production or
	execution of application programs but which is not specific to
	any particular application.  Examples of system software would
	include the {operating system}, {compilers}, editors and
	sorting programs.

	Examples of application programs would include an accounts
	package or a {CAD} program.  Other broad classes of
	application software include {real-time} software, {business
	software}, scientific and engineering software, {embedded
	software}, personal computer software and {artificial
	intelligence} software.

	Software includes both {source code} written by humans and
	executable {machine code} produced by {assemblers} or
	{compilers}.  It does not usually include the data processed
	by programs unless this is in a format such as {multimedia}
	which depends on the use of computers for its presentation.
	This distinction becomes unclear in cases such as {spread
	sheets} which can contain both instructions (formulae and
	{macros}) and data.  There are also various intermediate
	compiled or {semi-compiled}, forms of software such as
	{library} files and {byte-code}.

	Some claim that {documentation} (both paper and electronic) is
	also software.  Others go further and define software to be
	programs plus documentation though this does not correspond
	with common usage.

	The noun "program" describes a single, complete and
	more-or-less self-contained list of instructions, often stored
	in a single {file}, whereas "code" and "software" are
	uncountable nouns describing some number of instructions which
	may constitute one or more programs or part thereof.  Most
	programs, however, rely heavily on various kinds of {operating
	system} software for their execution.  The nounds "code" and
	"software" both refer to the same thing but "code" tends to
	suggest an interest in the implementation details whereas
	"software" is more of a user's term.

	(2002-07-21)

1. <electronics> {push-button}.

	2. <operating system> A graphical representation of an
	electrical {push-button} appearing as part of a {graphical
	user interface}.  Moving the {mouse pointer} over the
	graphical button and pressing one of the physical mouse
	buttons starts some software action such as closing a window
	or deleting a file.

	See also {radio button}.

	(1997-07-07)

<programming> (API, or "application programming interface")
	The interface (calling conventions) by which an {application
	program} accesses {operating system} and other services.  An
	API is defined at {source code} level and provides a level of
	{abstraction} between the application and the {kernel} (or
	other privileged utilities) to ensure the {portability} of the
	code.

	An API can also provide an interface between a {high level
	language} and lower level utilities and services which were
	written without consideration for the {calling conventions}
	supported by compiled languages.  In this case, the API's main
	task may be the translation of parameter lists from one format
	to another and the interpretation of {call-by-value} and
	{call-by-reference} arguments in one or both directions.

	(1995-02-15)

1. To prepare to read or write a file.  This usually involves
	checking whether the file already exists and that the user has
	the necessary authorisation to read or write it.  The result
	of a successful open is usually some kind of {capability}
	(e.g. a {Unix} {file descriptor}) - a token that the user
	passes back to the system in order to access the file without
	further checks and finally to close the file.

	2. Abbreviation for "open (or left) parenthesis" - used when
	necessary to eliminate oral ambiguity.  To read aloud the LISP
	form (DEFUN FOO (X) (PLUS X 1)) one might say: "Open defun
	foo, open eks close, open, plus eks one, close close."

	3. Non-proprietary.  An open {standard} is one which can be
	used without payment.

	[{Jargon File}]

	(1995-01-31)

<language, programming> (Or "source", or rarely "source
	language") The form in which a computer program is written by
	the programmer.  Source code is written in some formal
	programming language which can be compiled automatically into
	{object code} or {machine code} or executed by an
	{interpreter}.

	(1995-01-05)

1. <programming> The prototype for an {object} in an
	{object-oriented language}; analogous to a {derived type} in a
	{procedural language}.  A class may also be considered to be a
	set of objects which share a common structure and behaviour.
	The structure of a class is determined by the {class
	variables} which represent the {state} of an object of that
	class and the behaviour is given by a set of {methods}
	associated with the class.

	Classes are related in a {class hierarchy}.  One class may be
	a specialisation (a "{subclass}") of another (one of its
	"{superclasses}") or it may be composed of other classes or it
	may use other classes in a {client-server} relationship.  A
	class may be an {abstract class} or a {concrete class}.

	See also {signature}.

	2. <programming> See {type class}.

	3. <networking> One of three types of {Internet addresses}
	distinguished by their most significant bits.

	3. <language> A language developed by the {Andrew Project}.
	It was one of the first attempts to add {object-oriented}
	features to {C}.

	(1995-05-01)

1. <file system> {hard link} or {symbolic link}.

	2. <hypertext> {hyperlink}.

	(1997-10-22)

1. <mathematics> A {set} containing a certain number of
	objects selected from another set.

	The number of combinations of r objects chosen from a set of n
	is

		n C r = n! / ((n-r)! r!)

	where "n C r" is normally with n and r as subscripts or as n
	above r in parentheses.

	See also {permutation}.

	2. <reduction> In the theory of {combinators}, a combination
	denotes an expression in which {function application} is the
	only operation.

	(1995-04-10)

1. <architecture> {cache hit}.

	2. <World-Wide Web> A request to a {web server} from a {web
	browser} or other {client} (e.g. a {robot}).

	The number of hits on a server may be important for
	determining advertising revenue.

	In the course of loading a single {web page}, a browser may
	hit a web server many times e.g. to retrieve the page itself
	and each {image} on the page.  In contrast, caching by
	browsers and {web proxies} reduces the number of hits on the
	server because some requests are satisfied from the cache.

	3. <jargon> To press and release a key on the keyboard.  Some
	prefer the less aggressive "tap".

	(2000-02-20)

<programming> One of a sequence of copies of a program, each
	incorporating new modifications.  Each version is usually
	identified by a number, commonly of the form X.Y where X is
	the major version number and Y is the release number.
	Typically an increment in X (with Y reset to zero) signifies a
	substantial increase in the function of the program or a
	partial or total re-implementation, whereas Y increases each
	time the progam is changed in any way and re-released.

	Version numbers are useful so that the user can know if the
	program has changed ({bugs} have been fixed or new functions
	added) since he obtained his copy and the programmer can tell
	if a bug report relates to the current version.  It is thus
	always important to state the version when reporting bugs.
	Statements about compatibility between different software
	components should always say which versions they apply to.

	See {change management}.

	(1997-12-07)

1. <data, graphics> Data representing a two-dimensional scene.
	A digital image is composed of {pixels} arranged in a
	rectangular array with a certain height and width.  Each pixel
	may consist of one or more {bits} of information, representing
	the brightness of the image at that point and possibly
	including colour information encoded as {RGB} triples.

	{Images} are usually taken from the real world via a {digital
	camera}, {frame grabber}, or {scanner}; or they may be
	generated by computer, e.g. by {ray tracing} software.

	See also {image formats}, {image processing}.

	(1994-10-21)

	2. <mathematics> The image (or range) of a {function} is the
	set of values obtained by applying the function to all
	elements of its {domain}.  So, if f : D -> C then the set f(D)
	= \{ f(d) | d in D \} is the image of D under f.  The image is
	a subset of C, the {codomain}.

	(2000-01-19)

1. <robotics> A mechanical device for performing a task which
	might otherwise be done by a human, e.g. spraying paint on
	cars.

	See also {cybernetics}.

	2. <chat> An {IRC} or {MUD} user who is actually a program.
	On IRC, typically the robot provides some useful service.
	Examples are {NickServ}, which tries to prevent random users
	from adopting {nicks} already claimed by others, and MsgServ,
	which allows one to send {asynchronous} messages to be
	delivered when the recipient signs on.  Also common are
	"annoybots", such as KissServ, which perform no useful
	function except to send cute messages to other people.
	Service robots are less common on {MUDs}; but some others,
	such as the "Julia" robot active in 1990--91, have been
	remarkably impressive {Turing test} experiments, able to pass
	as human for as long as ten or fifteen minutes of
	conversation.

	3. <World-Wide Web> {spider}.

	[{Jargon File}]

	(1996-03-23)

<file system> An element of data storage in a {file system}.

	The history of computing is rich in varied kinds of files and
	{file systems}, whether ornate (e.g., {Macintosh file system}
	for a well-known case) or deficient (e.g., many simple
	pre-1980s file systems don't allow {directories}).

	However, the prototypical file has these characteristics:

	* It is a single sequence of bytes (but consider {Macintosh}
	{resource forks}).

	* It has a finite length, unlike, e.g. a {Unix} {device}.

	* It is stored in a {non-volatile storage} medium (but see
	{ramdrive}).

	* It exists (nominally) in a {directory}.

	* It has a name that it can be referred to by in file
	operations, possibly in combination with its {path}.

	Additionally, a file system may associate other information
	with a file, such as {permission} bits or other {file
	attributes}; timestamps for file creation, last revision, and
	last access; revision numbers (a` la VMS), and other kinds of
	{magic}.

	Compare: {document}.

	(1997-04-08)

<graphics> (AWT) {Java}'s {platform}-independent {windowing},
	graphics, and user-interface {toolkit}.  The AWT is part of
	the {Java Foundation Classes} (JFC) - the standard {API} for
	providing a {graphical user interface} (GUI) for a Java
	program.

	Compare: {SWING}.

	["Java in a Nutshell", O'Reilly].

	{Home (http://java.sun.com/products/jdk/awt/)}.

	(2000-07-26)

<language> Beginner's All-purpose Symbolic Instruction Code.
	A simple language oroginally designed for ease of programming
	by students and beginners.

	BASIC exists in many dialects, and is popular on
	{microcomputers} with sound and graphics support.  Most micro
	versions are {interactive} and {interpreted}.

	BASIC has become the leading cause of brain-damage in
	proto-hackers.  This is another case (like {Pascal}) of the
	cascading lossage that happens when a language deliberately
	designed as an educational toy gets taken too seriously.  A
	novice can write short BASIC programs (on the order of 10-20
	lines) very easily; writing anything longer is (a) very
	painful, and (b) encourages bad habits that will make it
	harder to use more powerful languages well.  This wouldn't be
	so bad if historical accidents hadn't made BASIC so common on
	low-end micros.  As it is, it ruins thousands of potential
	wizards a year.

	Originally, all references to code, both {GOTO} and GOSUB
	(subroutine call) referred to the destination by its line
	number.  This allowed for very simple editing in the days
	before {text editors} were considered essential.  Just typing
	the line number deleted the line and to edit a line you just
	typed the new line with the same number.  Programs were
	typically numbered in steps of ten to allow for insertions.
	Later versions, such as {BASIC V}, allow {GOTO}-less
	{structured programming} with named {procedures} and
	{functions}, IF-THEN-ELSE-ENDIF constructs and {WHILE} loops
	etc.

	Early BASICs had no graphic operations except with graphic
	characters.  In the 1970s BASIC {interpreters} became standard
	features in {mainframes} and {minicomputers}.  Some versions
	included {matrix} operations as language {primitives}.

	A {public domain} {interpreter} for a mixture of {DEC}'s
	{MU-Basic} and {Microsoft Basic} is {here
	(ftp://oak.oakland.edu/pub/Unix-c/languages/basic/basic.tar-z)}.
	A {yacc} {parser} and {interpreter} were in the
	comp.sources.unix archives volume 2.

	See also {ANSI Minimal BASIC}, {bournebasic}, {bwBASIC},
	{ubasic}, {Visual Basic}.

	[{Jargon File}]

	(1995-03-15)

<unit> (b) {binary} digit.

	The unit of information; the amount of information obtained by
	asking a yes-or-no question; a computational quantity that can
	take on one of two values, such as false and true or 0 and 1;
	the smallest unit of storage - sufficient to hold one bit.

	A bit is said to be "set" if its value is true or 1, and
	"reset" or "clear" if its value is false or 0.  One speaks of
	setting and clearing bits.  To {toggle} or "invert" a bit is
	to change it, either from 0 to 1 or from 1 to 0.

	The term "bit" first appeared in print in the computer-science
	sense in 1949, and seems to have been coined by the eminent
	statistician, {John Tukey}.  Tukey records that it evolved
	over a lunch table as a handier alternative to "bigit" or
	"binit".

	See also {flag}, {trit}, {mode bit}, {byte}, {word}.

	[{Jargon File}]

	(2002-01-22)

1. <database> A value used to identify a {record} in a
	database, derived by applying some fixed function to the
	record.  The key is often simply one of the {fields} (a
	{column} if the database is considered as a table with records
	being rows, see "{key field}").  Alternatively the key may be
	obtained by applying some function, e.g. a {hash function}, to
	one or more of the fields.  The set of keys for all records
	forms an {index}.  Multiple indexes may be built for one
	database depending on how it is to be searched.

	2. <cryptography> A value which must be fed into the
	{algorithm} used to decode an encrypted message in order to
	reproduce the original {plain text}.  Some encryption schemes
	use the same (secret) key to encrypt and decrypt a message,
	but {public key encryption} uses a "private" (secret) key and
	a "public" key which is known by all parties.

	3. <hardware> An electromechanical {keyboard} button.

	(2003-07-04)