<system> The degree to which a system suffers degradation or
	interruption in its service to the customer as a consequence
	of failures of one or more of its parts.

	One of the components of {RAS}.

	(2000-08-13)

<programming> (Or "released version", "baseline") A version of
	a piece of software which has been made public (as opposed to
	a version that is in development, or otherwise unreleased).

	A release is either a {major release}, a {revision}, or a
	{bugfix}.

	Pre-release versions may be called {alpha test}, or {beta
	test} versions.

	See {change management}.

	(1996-08-04)

The ability of software and hardware on multiple machines from
	multiple vendors to communicate.

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)

<jargon> 1. A good property or behaviour (as of a program).
	Whether it was intended or not is immaterial.

	2. An intended property or behaviour (as of a program).
	Whether it is good or not is immaterial (but if bad, it is
	also a {misfeature}).

	3. A surprising property or behaviour; in particular, one that
	is purposely inconsistent because it works better that way -
	such an inconsistency is therefore a {feature} and not a
	{bug}.  This kind of feature is sometimes called a {miswart}.

	4. A property or behaviour that is gratuitous or unnecessary,
	though perhaps also impressive or cute.  For example, one
	feature of {Common LISP}'s "format" function is the ability to
	print numbers in two different Roman-numeral formats (see
	{bells, whistles, and gongs}).

	5. A property or behaviour that was put in to help someone
	else but that happens to be in your way.

	6. A bug that has been documented.  To call something a
	feature sometimes means the author of the program did not
	consider the particular case, and that the program responded
	in a way that was unexpected but not strictly incorrect.  A
	standard joke is that a bug can be turned into a {feature}
	simply by documenting it (then theoretically no one can
	complain about it because it's in the manual), or even by
	simply declaring it to be good.  "That's not a bug, that's a
	feature!" is a common catch-phrase.  Apparently there is a
	Volkswagen Beetle in San Francisco whose license plate reads
	"FEATURE".

	See also {feetch feetch}, {creeping featurism}, {wart}, {green
	lightning}.

	The relationship among bugs, features, misfeatures, warts and
	miswarts might be clarified by the following hypothetical
	exchange between two hackers on an airliner:

	A: "This seat doesn't recline."

	B: "That's not a bug, that's a feature.  There is an emergency
	exit door built around the window behind you, and the route
	has to be kept clear."

	A: "Oh.  Then it's a misfeature; they should have increased
	the spacing between rows here."

	B: "Yes.  But if they'd increased spacing in only one section
	it would have been a wart - they would've had to make
	nonstandard-length ceiling panels to fit over the displaced
	seats."

	A: "A miswart, actually.  If they increased spacing throughout
	they'd lose several rows and a chunk out of the profit margin.
	So unequal spacing would actually be the Right Thing."

	B: "Indeed."

	"Undocumented feature" is a common euphemism for a {bug}.

	7. An attribute or function of a {class} in {Eiffel}.

	[{Jargon File}]

	(1995-10-22)

After-sale handholding; something many software vendors
	promise but few deliver.  To hackers, most support people are
	useless - because by the time a hacker calls support he or she
	will usually know the software and the relevant manuals better
	than the support people (sadly, this is *not* a joke or
	exaggeration).  A hacker's idea of "support" is a tte--tte
	or exchange of {electronic mail} with the software's designer.

	[{Jargon File}]

	(1995-02-15)

1. {application program}.

	2. {function application}.

<programming> Combining software or hardware components or
	both into an overall system.

	(1996-05-22)

<software, hardware> A term that describes a language,
	software application or hardware device that works on more
	than one system {platform} (e.g. {Unix}, {Microsoft Windows},
	{Macintosh}).  E.g. {Netscape Navigator}, {Java}.

	(1998-02-24)

<operating system, programming> The ease with which a piece of
	software (or {file format}) can be "ported", i.e. made to run
	on a new {platform} and/or compile with a new {compiler}.

	The most important factor is the language in which the
	software is written and the most portable language is almost
	certainly {C} (though see {Vaxocentrism} for counterexamples).
	This is true in the sense that C compilers are available for
	most systems and are often the first compiler provided for a
	new system.  This has led several compiler writers to compile
	other languages to C code in order to benefit from its
	portability (as well as the quality of compilers available for
	it).

	The least portable type of language is obviously {assembly
	code} since it is specific to one particular (family of)
	{processor}(s).  It may be possible to translate mechanically
	from one assembly code (or even {machine code}) into another
	but this is not really portability.  At the other end of the
	scale would come {interpreted} or {semi-compiled} languages
	such as {LISP} or {Java} which rely on the availability of a
	portable {interpreter} or {virtual machine} written in a lower
	level language (often C for the reasons outlined above).

	The act or result of porting a program is called a "port".
	E.g. "I've nearly finished the {Pentium} port of my big bang
	simulation."

	Portability is also an attribute of {file formats} and depends
	on their adherence to {standards} (e.g. {ISO 8859}) or the
	availability of the relevant "viewing" software for different
	{platforms} (e.g. {PDF}).

	(1997-06-18)

<language, programming> (J2SE) {Sun}'s {Java} programming
	platform aimed at network-oriented enterprise applications.
	J2SE comprises the {Java 2 Software Development Kit} (SDK) and
	the {Java 2 Run-Time Environment}.

	See also the Micro edition {J2ME} and the Enterprise edition
	{J2EE}.

	{Java 2 Platform (http://www.javasoft.com/j2se/)}.

	(2000-04-20)

<text> /ledding/ The spacing between lines of {text}.  This is
	defined when a {font} is designed but can often be altered in
	order to change the appearance of the text or for special
	effects.  It is measured in {points} and is normally 120% of
	the height of the text.

	See also {kerning}, {tracking}.

	(1996-06-07)

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)

<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)

<programming> Waffle for "{features}" or "function".  The
	capabilities or behaviours of a program, part of a program, or
	system, seen as the sum of its {features}.  Roughly, "the
	things it can do".  Generally used in a comparative sense,
	e.g. "The latest update adds some useful functionality".

	(1997-07-14)

1. <programming> A manifestation of an {error} in {software}.
	A fault, if encountered, may cause a {failure}.

	2. <architecture> {page fault}.

	(1996-05-14)

<reliability> Automatically switching to a redundant or
	standby server, system, or network upon the failure or
	abnormal termination of the currently-active server, system,
	or network (a "{hot standby}" or "{warm standby}").  Failover
	happens without human intervention.  This feature is usually
	built-in to expensive systems which must be available
	continuously.

	(2001-03-19)

<operating system> ("back up" when used as a verb) A spare
	copy of a file, file system, or other resource for use in the
	event of failure or loss of the original.

	The term commonly refers to a copy of the files on a
	computer's {disks}, made periodically and kept on {magnetic
	tape} or other removable medium (also called a "{dump}").

	This essential precaution is neglected by most new computer
	users until the first time they experience a {disk crash} or
	accidentally delete the only copy of the file they have been
	working on for the last six months.  Ideally the backup copies
	should be kept at a different site or in a fire safe since,
	though your hardware may be insured against fire, the data on
	it is almost certainly neither insured nor easily replaced.

	See also {backup software}, {differential backup},
	{incremental backup}, {full backup}.  Compare {archive},
	{source code management}.

	(2004-03-16)

<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)

An attempt to classify the degree of sophistication of
	programming languages.

	See {First generation language} -- {Fifth generation
	language}.

	(1995-06-15)

A quantity which is multiplied by another quantity.  See
	{coefficient of X}.  See also {divisor}.

	[{Jargon File}]

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)

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> 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)

<jargon> To transfer data from one computer to another.
	Downloading usually refers to transfer from a larger "host"
	system (especially a {server} or {mainframe}) to a smaller
	"client" system, especially a {microcomputer} or specialised
	peripheral, and "{upload}" usually means from small to large.

	Others hold that, technically, download means "receive" and
	upload means "send", irrespective of the size of the systems
	involved.

	Note that in communications between ground and space,
	space-to-earth transmission is always "down" and the reverse
	"up", regardless of size.  So far the in-space machines have
	invariably been smaller; thus the upload/download distinction
	has been reversed from its usual sense.

	[{Jargon File}]

	(2003-11-04)

1. To feed data through any {compression} {algorithm}.

	2. <tool> The {Unix} program "compress", now largely
	supplanted by {gzip}.

	Unix compress was written in {C} by Joseph M. Orost, James
	A. Woods et al., and was widely circulated via {Usenet}.  It
	uses the {Lempel-Ziv Welch} {algorithm} and normally produces
	files with the suffix ".Z".

	Compress uses variable length codes.  Initially, nine-bit
	codes are output until they are all used.  When this occurs,
	ten-bit codes are used and so on, until an
	implementation-dependent maximum is reached.

	After every 10 {kilobytes} of input the compression ratio is
	checked.  If it is decreasing then the entire string table is
	discarded and information is collected from scratch.

1. <filename extension> {filename extension}.

	2. <programming> A {feature} or piece of {code} which
	{extends} a program's {functionality}, e.g. a {plug-in}.

	(1997-06-21)

<programming> An unwanted and unintended property of a program
	or piece of hardware, especially one that causes it to
	malfunction.  Antonym of {feature}.  E.g. "There's a bug in
	the editor: it writes things out backward."  The
	identification and removal of bugs in a program is called
	"{debugging}".

	Admiral {Grace Hopper} (an early computing pioneer better
	known for inventing {COBOL}) liked to tell a story in which a
	technician solved a {glitch} in the {Harvard Mark II machine}
	by pulling an actual insect out from between the contacts of
	one of its relays, and she subsequently promulgated {bug} in
	its hackish sense as a joke about the incident (though, as she
	was careful to admit, she was not there when it happened).
	For many years the logbook associated with the incident and
	the actual bug in question (a moth) sat in a display case at
	the Naval Surface Warfare Center (NSWC).  The entire story,
	with a picture of the logbook and the moth taped into it, is
	recorded in the "Annals of the History of Computing", Vol. 3,
	No. 3 (July 1981), pp. 285--286.

	The text of the log entry (from September 9, 1947), reads
	"1545 Relay #70 Panel F (moth) in relay.  First actual case of
	bug being found".  This wording establishes that the term was
	already in use at the time in its current specific sense - and
	Hopper herself reports that the term "bug" was regularly
	applied to problems in radar electronics during WWII.

	Indeed, the use of "bug" to mean an industrial defect was
	already established in Thomas Edison's time, and a more
	specific and rather modern use can be found in an electrical
	handbook from 1896 ("Hawkin's New Catechism of Electricity",
	Theo. Audel & Co.)  which says: "The term "bug" is used to a
	limited extent to designate any fault or trouble in the
	connections or working of electric apparatus."  It further
	notes that the term is "said to have originated in
	{quadruplex} telegraphy and have been transferred to all
	electric apparatus."

	The latter observation may explain a common folk etymology of
	the term; that it came from telephone company usage, in which
	"bugs in a telephone cable" were blamed for noisy lines.
	Though this derivation seems to be mistaken, it may well be a
	distorted memory of a joke first current among *telegraph*
	operators more than a century ago!

	Actually, use of "bug" in the general sense of a disruptive
	event goes back to Shakespeare!  In the first edition of
	Samuel Johnson's dictionary one meaning of "bug" is "A
	frightful object; a walking spectre"; this is traced to
	"bugbear", a Welsh term for a variety of mythological monster
	which (to complete the circle) has recently been reintroduced
	into the popular lexicon through fantasy {role-playing games}.

	In any case, in jargon the word almost never refers to
	insects.  Here is a plausible conversation that never actually
	happened:

	"There is a bug in this ant farm!"

	"What do you mean?  I don't see any ants in it."

	"That's the bug."

	[There has been a widespread myth that the original bug was
	moved to the Smithsonian, and an earlier version of this entry
	so asserted.  A correspondent who thought to check discovered
	that the bug was not there.  While investigating this in late
	1990, your editor discovered that the NSWC still had the bug,
	but had unsuccessfully tried to get the Smithsonian to accept
	it - and that the present curator of their History of
	American Technology Museum didn't know this and agreed that it
	would make a worthwhile exhibit.  It was moved to the
	Smithsonian in mid-1991, but due to space and money
	constraints has not yet been exhibited.  Thus, the process of
	investigating the original-computer-bug bug fixed it in an
	entirely unexpected way, by making the myth true!  - ESR]

	[{Jargon File}]

	(1999-06-29)