<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. <hardware> An electrical conductor.  For distances larger
	than a breadbox, a single line may consist of two electrical
	conductors in twisted, parallel, or concentric arrangement
	used to transport one logical signal.

	By extension, a (usually physical) medium such as an {optical
	fibre} which carries a signal.

	(1995-09-29)

<programming> A sequence of {data} values, usually {bytes},
	which usually stand for {characters} (a "character string").
	The {mapping} between values and characters is determined by
	the {character set} which is itself specified implcitly or
	explicitly by the environment in which the string is being
	interpreted.

	The most common character set is {ASCII} but, since the late
	1990s, there has been increased interest in larger character
	sets such as {Unicode} where each character is represented by
	more than eight {bits}.

	Most programming languages consider strings (e.g.
	"124:shabooya:\n", "hello world") basically distinct from
	numbers which are typically stored in fixed-length {binary} or
	{floating-point} representation.

	A {bit string} is a sequence of {bits}.

	(1999-12-21)

<architecture> {Data} transferred from a computer system to
	the outside world via some kind of {output device}.

	Opposite: {input}.

	(1997-04-28)

<language, text> An {SGML}, {HTML}, or {XML} {token}
	representing the beginning (start tag: "<p ...>") or end (end
	tag: "</p>") of an {element}.  In normal SGML {syntax} (and
	always in {XML}), a tag starts with a "<" and ends with an
	">".

	In {HTML} jargon, the term "tag" is often used for an
	"{element}".

	(2001-01-31)

<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)

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)

<language, text> (XML) An initiative from the {W3C} defining
	an "extremely simple" dialect of {SGML} suitable for use on
	the {World-Wide Web}.

	{(http://www.w3.org/XML/)}.

	[Relationship to the {XSL} forthcoming subset of {DSSSL}?]

	(1997-11-20)

In {object-oriented programming} sending a message to an
	{object} (to invoke a {method}) is equivalent to calling a
	{procedure} in traditional programming languages, except that
	the actual code executed may only be selected at run time
	depending on the {class} of the object.  Thus, in response to
	the message "drawSelf", the method code invoked would be
	different if the target object were a circle or a square.

	(1995-02-16)

1. <operating system, software> The sequence of states of an
	executing {program}.  A process consists of the program {code}
	(which may be shared with other processes which are executing
	the same program), private data, and the state of the
	{processor}, particularly the values in its {registers}.  It
	may have other associated resources such as a {process
	identifier}, open files, {CPU time} limits, {shared memory},
	{child processes}, and {signal handlers}.

	One process may, on some {platforms}, consist of many
	{threads}.  A {multitasking} {operating system} can run
	multiple processes {concurrently} or in {parallel}, and allows
	a process to spawn "child" processes.

	(2001-06-16)

	2. <business> The sequence of activities, people, and systems
	involved in carrying out some business or achieving some
	desired result.  E.g. software development process, project
	management process, configuration management process.

	(2001-06-16)

1. <data, programming> One of the items of data in an {array}.

	2. <language, text> One kind of node in an {SGML}, {HTML}, or
	{XML} {document} {tree}.  An SGML element is typically
	represented by a start {tag} ("<p>") and an end tag ("</p>").
	In some SGML implementations, some tags are omissible, as with
	"</p>" in {HTML}.

	The start tag can contain {attributes} ("<p lang="en-UK"
	class='stuff'>"), which are an unordered set of key-value
	bindings for that element.  Both the start tag and end tag for
	an element typically contain the "tag name" (also called the
	"{GI}" or generic identifier) for that element.

	In {XML}, an element is always represented either by an
	explicit start tag and end tag, or by an empty element tag
	("<img src='thing.{png}' alt='a dodad' />").

	Other kinds of SGML node are: a section of character data
	("foo"), a comment ("<!-- bar -->"), a markup declaration
	("<!ENTITY reg CDATA '&#174'>"), or a processing instruction
	("<?xml-stylesheet href="shop-english.xsl" type="text/xsl"
	?>").

	(2001-01-30)

1. Executable code, especially a "pure code" portion shared
	between multiple instances of a program running in a
	{multitasking} {operating system}.

	Compare {English}.

	2. Textual material in the mainstream sense; data in ordinary
	{ASCII} or {EBCDIC} representation (see {flat ASCII}).  "Those
	are text files; you can review them using the editor."

	These two contradictory senses confuse hackers too.

	[{Jargon File}]

	(1995-03-16)

<electronics> The quantity of {charge} per unit time, measured
	in Amperes (Amps, A).  By historical convention, the sign of
	current is positive for currents flowing from positive to
	negative {potential}, but experience indicates that electrons
	are negatively charged and flow in the opposite direction.

	(1995-10-05)

<mathematics, data> (Or "child", "successor") In a {tree}, a
	{node} pointed to by a {parent}, i.e. another node closer to
	the {root node}.

	(1998-11-14)

1. A point or vertex in a {graph}.

	2. {network node}.

	3. A {hypertext} document.

1. <unit, text> (Sometimes abbreviated "pt") The unit of
	length used in {typography} to specify text character height,
	{rule} width, and other small measurements.

	There are six slightly different definitions: {Truchet point},
	{Didot point}, {ATA point}, {TeX point}, {Postscript point},
	and {IN point}.

	In Europe, the most commonly used is Didot and in the US, the
	formerly standard ATA point has essentially been replaced by
	the PostScript point due to the demise of traditional
	typesetting systems and rise of desktop computer based systems
	running software such as {QuarkXPress}, {Adobe InDesign} and
	{Adobe Pagemaker}.

	There are 20 {twips} in a point and 12 points in a {pica}
	(known as a "Cicero" in the Didot system).

	{Different point systems
	(http://www.vakcer.com/oberon/dtp/fonts/point.htm)}.

	(2004-12-23)

	2. <hardware> To move a {pointing device} so that the
	on-screen pointer is positioned over a certain object on the
	screen such as a {button} in a {graphical user interface}.  In
	most {window systems} it is then necessary to {click} a
	(physical) button on the pointing device to activate or select
	the object.  In some systems, just pointing to an object is
	known as "mouse-over" {event} which may cause some help text
	(called a "tool tip" in {Windows}) to be displayed.

	(2001-05-21)

<operating system> A character string which tells a program to
	perform a specific action.  Most commands take {arguments}
	which either modify the action performed or supply it with
	input.  Commands may be typed by the user or read from a file
	by a {command interpreter}.  It is also common to refer to
	menu items as commands.

	(1997-06-21)

<data> A named value or relationship that exists for some or
	all {instances} of some {entity} and is directly associated
	with that instance.

	Examples include the {href} attribute of an {HTML} {anchor}
	element, the columns of a database table considered as
	attributes of each row, and the {members} ({properties} and
	{methods} of an {object} in {OOP}.  This contrasts with the
	contents of some kind of container (e.g. an array), which are
	typically not named.  The contents of an {associative array},
	though they might be considered to be named by their key
	values, are not normally thought of as attributes.

	(2001-02-04)

<mathematics, data> A {directed acyclic graph}; i.e. a {graph}
	wherein there is only one route between any pair of {nodes},
	and there is a notion of "toward top of the tree" (i.e. the
	{root node}), and its opposite direction, toward the {leaves}.
	A tree with n nodes has n-1 edges.

	Although maybe not part of the widest definition of a tree, a
	common constraint is that no node can have more than one
	parent.  Moreover, for some applications, it is necessary to
	consider a node's {daughter} nodes to be an ordered {list},
	instead of merely a {set}.

	As a data structure in computer programs, trees are used in
	everything from {B-trees} in {databases} and {file systems}, to
	{game trees} in {game theory}, to {syntax trees} in a human or
	computer {languages}.

	(1998-11-12)

1. <networking> {segmentation}.

	2. The process, or result, of splitting a large area of free
	memory (on disk or in main memory) into smaller non-contiguous
	blocks.  This happens after many blocks have been allocated
	and freed.  For example, if there is 3 kilobytes of free space
	and two 1k blocks are allocated and then the first one (at the
	lowest address) is freed, then there will be 2k of free space
	split between the two 1k blocks.  The maximum size block that
	could then be allocated would be 1k, even though there was 2k
	free.  The solution is to "compact" the free space by moving
	the allocated blocks to one end (and thus the free space to
	the other).

	As modern file systems are used and files are deleted and
	created, the total free space becomes split into smaller
	non-contiguous blocks (composed of "{clusters}" or "{sectors}"
	or some other unit of allocation).  Eventually new files being
	created, and old files being extended, cannot be stored each
	in a single contiguous block but become scattered across the
	file system.  This degrades performance as multiple {seek}
	operations are required to access a single fragmented file.

	Defragmenting consolidates each existing file and the free
	space into a continuous group of sectors.  Access speed will
	be improved due to reduced seeking.

	The rate of fragmentation depends on the {algorithm} used to
	allocate space and the number and position of free sectors.  A
	nearly-full file system will fragment more quickly.

	{MSDOS} and {Microsoft Windows} use the simplest algorithm to
	allocate free clusters and so fragmentation occurs quickly.  A
	disk should be defragmented before fragmentation reaches 10%.

	See {garbage collection}.

	(1997-08-29)

<programming> A constant made available to a process, by
	inclusion in the executable text.  Most modern systems do not
	allow texts to modify themselves during execution, so literals
	are indeed constant; their value is written at compile-time
	and is read-only at run time.

	In contrast, values placed in variables or files and accessed
	by the process via a symbolic name, can be changed during
	execution.  This may be an asset.  For example, messages can
	be given in a choice of languages by placing the translation
	in a file.

	Literals are used when such modification is not desired.  The
	name of the file mentioned above (not its content), or a
	physical constant such as 3.14159, might be coded as a
	literal.  Literals can be accessed quickly, a potential
	advantage of their use.

	(1996-01-23)

<data> A data structure holding many values, possibly of
	different types, which is usually accessed sequentially,
	working from the head to the end of the tail - an "ordered
	list".  This contrasts with a (one-dimensional) {array}, any
	element of which can be accessed equally quickly.

	Lists are often stored using a cell and pointer arrangement
	where each value is stored in a cell along with an associated
	pointer to the next cell.  A special pointer, e.g. zero, marks
	the end of the list.  This is known as a (singly) "linked
	list".  A doubly linked list has pointers from each cell to
	both next and previous cells.

	An unordered list is a {set}.

	(1998-11-12)

<programming> Any piece of program code in a {high-level
	language} which, when (if) its execution terminates, returns a
	value.  In most programming languages, expressions consist of
	constants, variables, operators, functions, and {parentheses}.
	The operators and functions may be built-in or user defined.
	Languages differ on how expressions of different {types} may
	be combined - with some combination of explicit {casts} and
	implicit {coercions}.

	The {syntax} of expressions generally follows conventional
	mathematical notation, though some languages such as {Lisp} or
	{Forth} have their own idiosyncratic syntax.

	(2001-05-14)

1. Annoyingly complicated.  "{DWIM} is incredibly hairy."

	2. Incomprehensible.  "{DWIM} is incredibly hairy."

	3. Of people, high-powered, authoritative, rare, expert,
	and/or incomprehensible.  Hard to explain except in context:
	"He knows this hairy lawyer who says there's nothing to worry
	about."  See also {hirsute}.

	The adjective "long-haired" is well-attested to have been in
	slang use among scientists and engineers during the early
	1950s; it was equivalent to modern "hairy" and was very likely
	ancestral to the hackish use.  In fact the noun "long-hair"
	was at the time used to describe a hairy person.  Both senses
	probably passed out of use when long hair was adopted as a
	signature trait by the 1960s counterculture, leaving hackish
	"hairy" as a sort of stunted mutant relic.

	4. <topology> {hairy ball}.

	[{Jargon File}]

	(2001-03-29)

<operating system, programming> The process of carrying out
	the {instructions} in a computer program by a computer.

	See also {dry run}.

	(1996-05-13)

1. <application> Any specific type of {file} produced or
	edited by a specific {application}; usually capable of being
	printed.  E.g. "Word document", "Photoshop document", etc.

	2. <hypertext> A term used on some systems (e.g. {Intermedia})
	for a {hypertext} {node}.  It is sometimes used for a
	collection of nodes on related topics, possibly stored or
	distributed as one.

	3. <programming> To write {documentation} on a certain piece
	of code.

	(2003-10-25)

<digital signal processing> The result of measuring the
	amplitude of an analog signal at a specified time.  In
	{digital signal processing} a sample is a signed or unsigned
	number and the number of samples per second is called the
	{sample rate}.

	(2001-06-06)

1. <operating system> The {Unix} {superuser} account (with
	user name "root" and user ID 0) that overrides file
	permissions.  The term {avatar} is also used.  By extension,
	the privileged system-maintenance login on any {operating
	system}.

	See {root mode}, {go root}, {wheel}.

	[{Jargon File}]

	(1994-10-27)

	2. <operating system> {root directory}.

	(1996-11-21)

	3. <data> {root node}.

	(1998-11-14)

(RTF) An interchange format from {Microsoft} for exchange of
	documents between {Word} and other document preparation
	systems.

	(1994-12-08)

1. <tool> A program used primarily to create, manipulate,
	modify, or analyse other programs, such as a compiler or an
	editor or a cross-referencing program.  Opposite: {app},
	{operating system}.

	2. A {Unix} {application program} with a simple, "transparent"
	(typically text-stream) interface designed specifically to be
	used in programmed combination with other tools (see {filter},
	{plumbing}).

	3. <jargon> ({MIT}: general to students there) To work; to
	study (connotes tedium).  The {TMRC} Dictionary defined this
	as "to set one's brain to the grindstone".  See {hack}.

	4. <jargon, person> ({MIT}) A student who studies too much and
	hacks too little.  MIT's student humour magazine rejoices in
	the name "Tool and Die".

	[{Jargon File}]

	(1996-12-12)

1. <programming> An {address}, from the point of view of a
	programming language.  A pointer may be typed, with its {type}
	indicating the type of data to which it points.

	The terms "pointer" and "reference" are generally
	interchangable although particular programming languages often
	differentiate these two in subtle ways.  For example, {Perl}
	always calls them references, never pointers.  Conversely, in
	C, "pointer" is used, although "a reference" is often used to
	denote the concept that a pointer implements.

	{Anthony Hoare} once said:

	Pointers are like jumps, leading wildly from one part of the
	data structure to another.  Their introduction into high-level
	languages has been a step backward from which we may never
	recover.

	[C.A.R.Hoare "Hints on Programming Language Design", 1973,
	Prentice-Hall collection of essays and papers by Tony Hoare].

	2. <operating system> (Or "mouse pointer") An {icon}, usually
	a small arrow, that moves on the screen in response to
	movement of a {pointing device}, typically a {mouse}.  The
	pointer shows the user which object on the screen will be
	selected etc. when a mouse button is clicked.

	(1999-07-07)

<convention> (FAQ, or rarely FAQL, FAQ list) A document
	provided for many {Usenet} {newsgroups} (and, more recently,
	{World-Wide Web} services) which attempts to answer questions
	which new readers often ask.  These are maintained by
	volunteers and posted regularly to the newsgroup.  You should
	always consult the FAQ list for a group before posting to it
	in case your question or point is common knowledge.

	The collection of all FAQ lists is one of the most precious
	and remarkable resources on the {Internet}.  It contains a
	huge wealth of up-to-date expert knowledge on many subjects of
	common interest.  Accuracy of the information is greatly
	assisted by its frequent exposure to criticism by an
	interested, and occasionally well-informed, audience (the
	readers of the relevant newsgroup).

	The main {FTP archive} for FAQs is on a computer called {RTFM}
	at {MIT}, where they can be accessed either {by group
	(ftp://rtfm.mit.edu/pub/usenet-by-group/comp.answers/)} or {by
	hierarchy (ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/)}.
	There is another archive at {Imperial College
	(ftp://src.doc.ic.ac.uk/usenet/news-info/)}, London, UK and a
	{World-Wide Web} archive in {Ohio
	(http://www.cis.ohio-state.edu/hypertext/faq/usenet/top.html)},
	USA.

	The FAQs are also posted to {Usenet} newsgroups:
	{news:comp.answers}, {news:news.answers} and
	{news:alt.answers}.

	(1997-12-08)

1. <application, algorithm> To arrange a collection of items
	in some specified order.  The items - {records} in a file or
	data structures in memory - consist of one or more {fields} or
	members.  One of these fields is designated as the "sort key"
	which means the records will be ordered according to the value
	of that field.  Sometimes a sequence of key fields is
	specified such that if all earlier keys are equal then the
	later keys will be compared.  Within each field some ordering
	is imposed, e.g. ascending or descending numerical, {lexical
	ordering}, or date.

	Sorting is the subject of a great deal of study since it is a
	common operation which can consume a lot of computer time.
	There are many well-known sorting {algorithms} with different
	time and space behaviour and programming {complexity}.

	Examples are {quicksort}, {insertion sort}, {bubble sort},
	{heap sort}, and {tree sort}.  These employ many different
	data structures to store sorted data, such as {arrays},
	{linked lists}, and {binary trees}.

	2. <tool> The {Unix} utility program for sorting lines of
	files.

	{Unix manual page}: sort(1).

	(1997-02-12)

<company> (IBM) The best known American computer manufacturer,
	founded by Thomas J. Watson (born 1874-02-17), known as "Big
	Blue" after the colour of its logo.  IBM makes everything from
	{mainframes} to {personal computers} (PCs) and has been
	immensely successful in selling them, chiefly to business.  It
	has often been said that "Nobody has ever been sacked for
	buying IBM".

	The {IBM PC} in its various versions has been so successful
	that unqualified reference to a "PC" almost certainly means a
	PC from IBM, or one of the many brands of {clone} produced by
	other manufacturers to cash in on IBM's original success.

	Alternative expansions of "IBM" such as Inferior But
	Marketable; It's Better Manually; Insidious Black Magic; It's
	Been Malfunctioning; Incontinent Bowel Movement, illustrate
	the considerable antipathy most hackers have long felt toward
	the "industry leader" (see {fear and loathing}).

	Quarterly sales $15351M, profits $689M (Aug 1994).

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

	(1999-04-07)

<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)