The process of analysis, design, coding and testing software.

1. <operating system> A task running in the background (a
	background task) is detached from the terminal where it was
	started (and often running at a lower priority); opposite of
	{foreground}.  This means that the task's input and output
	must be from/to files (or other processes).

	Nowadays this term is primarily associated with {Unix}, but it
	appears to have been first used in this sense on {OS/360}.

	Compare {amp off}, {batch}, {slopsucker}.

	2. <jargon> For a human to do a task "in the background" is to
	do it whenever {foreground} matters are not claiming your
	undivided attention, and "to background" something means to
	relegate it to a lower priority.  "For now, we'll just print a
	list of nodes and links; I'm working on the graph-printing
	problem in the background."  Note that this implies ongoing
	activity but at a reduced level or in spare time, in contrast
	to mainstream "back burner" (which connotes benign neglect
	until some future resumption of activity).  Some people prefer
	to use the term for processing that they have queued up for
	their unconscious minds (often a fruitful tack to take upon
	encountering an obstacle in creative work).

	(1996-05-28)

<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> {fill-out form}.

	2. <library> (Xforms) A {GUI} component library for {X11}.

	(1998-03-24)

<programming> A computer system or process that requests a
	service of another computer system or process (a "{server}")
	using some kind of {protocol} and accepts the server's
	responses.  A client is part of a {client-server} software
	architecture.

	For example, a {workstation} requesting the contents of a file
	from a {file server} is a client of the file server.

	(1997-10-27)

<jargon> A {marketroid} term for something he wants to sell
	you without bothering you with the often dizzying distinctions
	between {hardware}, {software}, {services}, {applications},
	{file formats}, companies, brand names and {operating
	systems}.

	"{Flash} is a perfect image-streaming solution."  "What is
	it?"  "Um...  about a thousand dollars."

	See also: {technology}.

	(1998-07-07)

1. <mathematics> (Or "map", "mapping") If D and C are sets
	(the domain and codomain) then a function f from D to C,
	normally written "f : D -> C" is a subset of D x C such that:

	1. For each d in D there exists some c in C such that (d,c) is
	an element of f.  I.e. the function is defined for every
	element of D.

	2. For each d in D, c1 and c2 in C, if both (d,c1) and (d,c2)
	are elements of f then c1 = c2.  I.e. the function is uniquely
	defined for every element of D.

	See also {image}, {inverse}, {partial function}.

	2. <programming> Computing usage derives from the mathematical
	term but is much less strict.  In programming (except in
	{functional programming}), a function may return different
	values each time it is called with the same argument values
	and may have {side effects}.

	A {procedure} is a function which returns no value but has
	only {side-effects}.  The {C} language, for example, has no
	procedures, only functions.  {ANSI C} even defines a {type},
	{void}, for the result of a function that has no result.

	(1996-09-01)

1. <software> An occurrence or happening of significance to a
	task or program, such as the completion of an asynchronous
	input/output operation.  A task may wait for an event or any
	of a set of events or it may (request to) receive asynchronous
	notification (a {signal} or {interrupt}) that the event has
	occurred.

	See also {event-driven}.

	2. <data> A transaction or other activity that affects the
	records in a file.

	(2000-02-09)

(Scientific computation) Output from a computation that may
	not be significant but at least indicates that the program is
	running.  Numbers may be used to placate management, grant
	sponsors, etc.  "Making numbers" means running a program
	because output - any output, not necessarily meaningful output
	- is needed as a demonstration of progress.

	See {pretty pictures}, {math-out}, {social science number}.

	[{Jargon File}]

	(1995-01-13)

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)

<mathematics> (NaN) An {IEEE floating point} representation
	for the result of a numerical operation which cannot return a
	valid number value.  A NaN can result from multiplying an
	infinity by a zero, or from subtracting one infinity from
	another [what else?].

	NaN is encoded as a special {bit pattern} [what pattern?]
	which would otherwise represent a {floating-point} number.  It
	is used to signal error returns where other mechanisms are not
	convenient, e.g. a hardware {floating-point unit} and to allow
	errors to propagate through a calculation.

	Similar bit patterns represent positive and negative
	{overflow} and {underflow} and the positive and negative
	infinities resulting from {division by zero}.

	{Bit patterns
	(http://www.psc.edu/general/software/packages/ieee/ieee.html)}.

	[ANSI/IEEE Std 754-1985].

	[Correct?]

	(2001-04-01)

<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)

1. <database, information science> A user's (or {agent}'s)
	request for information, generally as a formal request to a
	{database} or {search engine}.

	{SQL} is the most common {database query language}.

	2. <character> {question mark}.

	(1997-04-09)

1. A program which provides some service to other ({client})
	programs.  The connection between client and server is
	normally by means of {message passing}, often over a
	{network}, and uses some {protocol} to encode the client's
	requests and the server's responses.  The server may run
	continuously (as a {daemon}), waiting for requests to arrive
	or it may be invoked by some higher level daemon which
	controls a number of specific servers ({inetd} on {Unix}).

	There are many servers associated with the {Internet}, such as
	those for {HTTP}, {Network File System}, {Network Information
	Service} (NIS), {Domain Name System} (DNS), {FTP}, {news},
	{finger}, {Network Time Protocol}.  On Unix, a long list can
	be found in /etc/services or in the {NIS} database "services".
	See {client-server}.

	2. A computer which provides some service for other computers
	connected to it via a network.  The most common example is a
	{file server} which has a local disk and services requests
	from remote clients to read and write files on that disk,
	often using {Sun}'s {Network File System} (NFS) {protocol} or
	{Novell Netware} on {PCs}.  Another common example is a {web
	server}.

	[{Jargon File}]

	(2003-12-29)

<chat, tool, networking, messaging> A {Unix} program and
	{protocol} supporting conversation between two or more users
	who may be logged into the same computer or different
	computers on a network.  Variants include {ntalk}, {ytalk},
	and {ports} or {emulators} of these programs for other
	{platforms}.

	{Unix} has the {talk} program and {protocol} and its variants
	{xtalk} and {ytalk} for the {X Window System}; {VMS} has
	{phone}; {Windows for Workgroups} has {chat}.  {ITS} also has
	a talk system.  These split the screen into separate areas for
	each user.

	{Unix}'s {write} command can also be used, though it does not
	attempt to separate input and output on the screen.

	Users of such systems are said to be in {talk mode} which has
	many conventional abbreviations and idioms.  Most of these
	survived into {chat} jargon, but many fell out of common use
	with the migration of {user} prattle from talk-like systems to
	{chat} systems in the early 1990s.  These disused
	talk-specific forms include:

	"BYE?" - are you ready to close the conversation?  This is the
	standard way to end a talk-mode conversation; the other person
	types "BYE" to confirm, or else continues the conversation.

	"JAM"/"MIN" - just a minute

	"O" - "over" (I have stopped talking).  Also "/" as in x/y - x
	over y, or two newlines (the latter being the most common).

	"OO" - "over and out" - end of conversation.

	"\" - Greek {lambda}.

	"R U THERE?" - are you there?

	"SEC" - wait a second.

	"/\/\/" - laughter.  But on a {MUD}, this usually means
	"earthquake fault".

	See also {talk bomb}.

	(1998-01-25)

<architecture> A sequence of {functional units} ("stages")
	which performs a task in several steps, like an assembly line
	in a factory.  Each functional unit takes inputs and produces
	outputs which are stored in its output {buffer}.  One stage's
	output buffer is the next stage's input buffer.  This
	arrangement allows all the stages to work in parallel thus
	giving greater throughput than if each input had to pass
	through the whole pipeline before the next input could enter.

	The costs are greater latency and complexity due to the need
	to synchronise the stages in some way so that different inputs
	do not interfere.  The pipeline will only work at full
	efficiency if it can be filled and emptied at the same rate
	that it can process.

	Pipelines may be synchronous or asynchronous.  A synchronous
	pipeline has a master clock and each stage must complete its
	work within one cycle.  The minimum clock period is thus
	determined by the slowest stage.  An asynchronous pipeline
	requires {handshaking} between stages so that a new output is
	not written to the interstage buffer before the previous one
	has been used.

	Many {CPUs} are arranged as one or more pipelines, with
	different stages performing tasks such as fetch instruction,
	decode instruction, fetch arguments, arithmetic operations,
	store results.  For maximum performance, these rely on a
	continuous stream of instructions fetched from sequential
	locations in memory.  Pipelining is often combined with
	{instruction prefetch} in an attempt to keep the pipeline
	busy.

	When a {branch} is taken, the contents of early stages will
	contain instructions from locations after the branch which
	should not be executed.  The pipeline then has to be flushed
	and reloaded.  This is known as a {pipeline break}.

	(1996-10-13)

<chat> (From SF fandom via {Usenet}) In My Humble Opinion.
	Also seen in variant forms such as IMO, IMNSHO (In My
	Not-So-Humble Opinion) and IMAO (In My Arrogant Opinion).

	[{Jargon File}]

	(1998-09-24)

1. To cause to be {broken} (in any sense).  "Your latest patch
	to the editor broke the paragraph commands."

	2. (Of a program) To stop temporarily, so that it may
	debugged.  The place where it stops is a "{breakpoint}".

	3. To send an {EIA-232} break (two character widths of line
	high) over a {serial line}.

	4. [Unix] To strike whatever key currently causes the tty
	driver to send SIGINT to the current process.  Normally,
	break, delete or {control-C} does this.

	5. "break break" may be said to interrupt a conversation (this
	is an example of verb doubling).  This usage comes from radio
	communications, which in turn probably came from landline
	telegraph/teleprinter usage, as badly abused in the Citizen's
	Band craze a few years ago.

	6. {pipeline break}.

	7. {break statement}.

	[{Jargon File}]

	(2004-03-24)

1. Not operating.  "The up escalator is down" is considered a
	humorous thing to say, and "The elevator is down" always
	means "The elevator isn't working" and never refers to what
	floor the elevator is on.  With respect to computers, this
	term has passed into the mainstream; the extension to other
	kinds of machine is still hackish.

	2. "go down" To stop functioning; usually said of the
	{system}.  The message from the {console} that every hacker
	hates to hear from the operator is "System going down in 5
	minutes".

	3. "take down", "bring down" To deactivate purposely, usually
	for repair work or {PM}.  "I'm taking the system down to work
	on that bug in the tape drive."  Occasionally one hears the
	word "down" by itself used as a verb in this sense.

	See {crash}; opposite: {up}.

	[{Jargon File}]

	(1994-12-07)

Using code developed for one {application program} in another
	application.  Traditionally achieved using program libraries.
	{Object-oriented programming} offers reusability of code via
	its techniques of {inheritance} and {genericity}.  {Class}
	libraries with {intelligent browsers} and {application
	generators} are under development to help in this process.
	{Polymorphic} {functional languages} also support reusability
	while retaining the benefits of {strong typing}.

	See also {DRAGOON}, {National Software Reuse Directory},
	{RLF}.

[{Usenet}] 1. To duplicate a portion (or whole) of another's
	message (typically with attribution to the source) in a reply
	or followup, for clarifying the context of one's response.
	See the discussion of inclusion styles under "Hacker Writing
	Style".

	2. [{C}] "#include <disclaimer.h>" has appeared in {sig
	blocks} to refer to a notional "standard {disclaimer} file".

	[{Jargon File}]