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)

<programming> The name given in {Smalltalk} and other
	{object-oriented languages} to a procedure or routine
	associated with one or more {classes}.  An {object} of a
	certain class knows how to perform actions, e.g. printing
	itself or creating a new instance of itself, rather than the
	function (e.g. printing) knowing how to handle different types
	of object.

	Different classes may define methods with the same name
	(i.e. methods may be {polymorphic}).  The term "method" is used
	both for a named operation, e.g. "PRINT" and also for the code
	which a specific class provides to perform tha
	t operation.

	Most methods operate on objects that are instances of a
	certain class.  Some object-oriented languages call these
	"object methods" to distinguish then from "{class methods}".

	In {Smalltalk}, a method is defined by giving its name,
	documentation, temporary local variables and a sequence of
	expressions separated by "."s.

	(2000-03-22)

<programming, operating system> (Or "application", "app") A
	complete, self-contained program that performs a specific
	function directly for the user.  This is in contrast to system
	software such as the {operating system} {kernel}, {server}
	processes and libraries which exists to support application
	programs.

	Editors for various kinds of documents, {spreadsheets}, and
	text formatters are common examples of applications.  Network
	applications include clients such as those for {FTP},
	{electronic mail}, {telnet} and {WWW}.

	The term is used fairly loosely, for instance, some might say
	that a client and server together form a distributed
	application, others might argue that editors and compilers
	were not applications but tools for building applications.

	One distinction between an application program and the
	operating system is that applications always run in "user
	mode" (or "non-privileged mode"), while operating systems and
	related utilities may run in "supervisor mode" (or "privileged
	mode").

	The term may also be used to distinguish programs which
	communicate via a {graphical user interface} from those which
	are executed from the {command line}.

	(1994-11-28)

<data processing, signal processing> Performing some
	predefined sequence of operations on an input to produce an
	output or change of internal state; activity specifically
	involving the computer's {CPU}.

	The term is often qualified: "{data processing}" treats
	{digital} data, "{signal processing}" treats {analog} data
	(possibly in digital form), "{word processing}" takes in typed
	human language input and produces digital documents, {image
	processing} transforms digital {images}.

	(2003-10-23)

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

	See also {dry run}.

	(1996-05-13)

<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)

<software> (Or "option", "flag", "switch", "option switch") An
	argument to a command that modifies its function rather than
	providing data.  Options generally start with "-" in {Unix} or
	"/" in {MS-DOS}.  This is usually followed by a single letter
	or occasionally a digit.

	Some commands require each option to be a separate argument,
	introduced by a new "-" or "/", others allow multiple option
	letters to be concatenated into a single argument with a
	single "-" or "/", e.g. "ls -al".  A few Unix commands
	(e.g. {ar}, {tar}) allow the "-" to be omitted.  Some options
	may or must be followed by a value, e.g. "cc prog.c -o prog",
	sometimes with and sometimes without an intervening space.

	{getopt} and {getopts} are commands for parsing command line
	options.  There is also a {C} library routine called getopt
	for the same purpose.

	(1996-12-11)

<software> Instructions for a computer in some programming
	language, often {machine language}.  The word "code" is often
	used to distinguish instructions from {data} (e.g. "The code
	is marked 'read-only'") whereas "{software}" is used in
	contrast with "{hardware}" and may consist of more than just
	code.

	(2000-04-08)

/knooth/ 1. {Donald Knuth}.

	2. ["The Art of Computer Programming", Donald E. Knuth]
	Mythically, the reference that answers all questions about
	data structures or algorithms.  A safe answer when you do not
	know: "I think you can find that in Knuth."

	Contrast {literature}.  See also {bible}.

	[{Jargon File}]

(Plural "indices" or "indexes")

	1. <programming> A number used to select an element of a list,
	vector, {array} or other sequence.  Such indices are nearly
	always non-negative integers but see {associative array}.

	2. <database> See {inverted index}.  [Other kinds?]

	3. <World-Wide Web> A {search engine}.

	4. <World-Wide Web> A {subject index}.

	4. <jargon> See {coefficient of X}.

	[{Jargon File}]

	(1997-04-09)

See also {complete graph}, {complete inference system},
	{complete lattice}, {complete metric space}, {complete partial
	ordering}, {complete theory}.

	[1. or 2. or both?]

	(1996-04-24)

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, compiler> Extra information associated with a
	particular point in a document or program.  Annotations may be
	added either by a {compiler} or by the programmer.  They are
	not usually essential to the correct function of the program
	but give hints to improve performance.

	2. <hypertext> A new commentary {node} linked to an existing
	node.  If readers, as well as authors, can annotate nodes,
	then they can immediately provide feedback if the information
	is misleading, out of date or plain wrong.

	(1995-11-26)

1. The {supervisor} program or {operating system} on a
	computer.

	2. The entire computer system, including input/output devices,
	the {supervisor} program or {operating system} and possibly
	other {software}.

	3. Any large program.

	4. Any method or {algorithm}.

	[{Jargon File}]

1. See {multithreading}.

	2. See {threaded code}.

	3. {topic thread}.

	[{Jargon File}]

1. <programming, compiler> Extra information associated with a
	particular point in a document or program.  Annotations may be
	added either by a {compiler} or by the programmer.  They are
	not usually essential to the correct function of the program
	but give hints to improve performance.

	2. <hypertext> A new commentary {node} linked to an existing
	node.  If readers, as well as authors, can annotate nodes,
	then they can immediately provide feedback if the information
	is misleading, out of date or plain wrong.

	(1995-11-26)

A safe program analysis is one which will not reach invalid
	conclusions about the behaviour of the program.  This may
	involve making safe approximations to properties of parts of
	the program.  A safe approximation is one which gives less
	information.

	For example, strictness analysis aims to answer the question
	"will this function evaluate its argument"?.  The two possible
	results are "definitely" and "don't know".  A safe
	approximation for "definitely" is "don't know".  The two
	possible results correspond to the two sets: "the set of all
	functions which evaluate their argument" and "all functions".
	A set can be safely approximated by another which contains it.

To produce something according to an {algorithm} or program or
	set of rules, or as a (possibly unintended) {side effect} of
	the execution of an algorithm or program.

	The opposite of {parse}.

	[{Jargon File}]

	(1995-06-15)

<file format, filename extension> (jar) A compressed {archive}
	file containing {Java} {class} files, filename extension:
	".jar".  The {Java Development Kit} contains a tool called
	"jar" for creating .jar files, similar to the standard {Unix}
	{tar} command.  As well as archiving and compressing the Java
	class files, it also inserts a "manifest" file which can
	contain information about the class files, such as a {digital
	signature}.  Combining class files into a single archive file
	makes it possible to download them in a single {HTTP}
	transaction.  This, and the {compression}, speeds up execution
	of Java programs delivered via the {Internet}.

	(2001}-02-03)

<computer, parallel> (Or "multi-tasking", "multiprogramming",
	"concurrent processing", "concurrency", "process scheduling")
	A technique used in an {operating system} for sharing a single
	processor between several independent jobs.  The first
	multitasking operating systems were designed in the early
	1960s.

	Under "{cooperative multitasking}" the running task decides
	when to give up the CPU and under "{pre-emptive multitasking}"
	(probably more common) a system process called the
	"{scheduler}" suspends the currently running task after it has
	run for a fixed period known as a "{time-slice}".  In both
	cases the scheduler is responsible for selecting the next task
	to run and (re)starting it.

	The running task may relinquish control voluntarily even in a
	pre-emptive system if it is waiting for some external {event}.
	In either system a task may be suspended prematurely if a
	hardware {interrupt} occurs, especially if a higher priority
	task was waiting for this event and has therefore become
	runnable.

	The scheduling {algorithm} used by the scheduler determines
	which task will run next.  Some common examples are
	{round-robin} scheduling, {priority scheduling}, {shortest job
	first} and {guaranteed scheduling}.

	Multitasking introduces {overheads} because the processor
	spends some time in choosing the next job to run and in saving
	and restoring tasks' state, but it reduces the worst-case time
	from job submission to completion compared with a simple
	{batch} system where each job must finish before the next one
	starts.  Multitasking also means that while one task is
	waiting for some external event, the {CPU} to do useful work
	on other tasks.

	A multitasking operating system should provide some degree of
	protection of one task from another to prevent tasks from
	interacting in unexpected ways such as accidentally modifying
	the contents of each other's memory areas.

	The jobs in a multitasking system may belong to one or many
	users.  This is distinct from {parallel processing} where one
	user runs several tasks on several processors.  {Time-sharing}
	is almost synonymous but implies that there is more than one
	user.

	{Multithreading} is a kind of multitasking with low
	{overheads} and no protection of tasks from each other, all
	threads share the same memory.

	(1998-04-24)

<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)

Specific computer hardware, as in the phrase
	"platform-independent".  It may also refer to a specific
	combination of hardware and {operating system} and/or
	{compiler}, as in "this program has been ported to several
	platforms".  It is also used to refer to support software for
	a particular activity, as in "This program provides a platform
	for research into routing protocols".

	(1994-12-07)