1. <storage> To move the head of a {disk drive} radially,
	i.e., to move from one {track} to another.

	2. <storage> To wind the {tape} to a given location.

	3. <programming> To move the pointer that marks the next {byte}
	to be read from or written to a {file}.

	(1997-07-15)

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. To copy {data} (often {program} {code} to be {run}) into
	{memory}, possibly {parsing} it somehow in the process.
	E.g. "{WordPerfect} can't load this {RTF} file - are you sure
	it didn't get corrupted in the {download}?"  Opposite of
	{save}.

	2. The degree to which a computer, {network}, or other
	resource is used, sometimes expressed as a percentage of the
	maximum available.  E.g. "What kind of CPU load does that
	program give?", "The network's constantly running at 100%
	load".  Sometimes used, by extension, to mean "to increase the
	level of use of a resource".  E.g. "Loading a spreadsheet
	really loads the CPU".  See also: {load balancing}.

	3. To {install} a piece of {software} onto a system.
	E.g. "The computer guy is gonna come load Excel on my laptop
	for me".  This usage is widely considered to be incorrect.

	(2002-07-02)

[IRC] To cause somebody to be removed from a {IRC} channel, an
	option only available to {CHOPs}.  This is an extreme measure,
	often used to combat extreme {flamage} or {flood}ing, but
	sometimes used at the chop's whim.  Compare {gun}.

	[{Jargon File}]

<networking> (Note: not capitalised) Any set of networks
	interconnected with {routers}.  The {Internet} is the biggest
	example of an internet.

	(1996-09-17)

<World-Wide Web> (URL, previously "Universal") A {standard}
	way of specifying the location of an object, typically a {web
	page}, on the {Internet}.  Other types of object are described
	below.  URLs are the form of address used on the {World-Wide
	Web}.  They are used in {HTML} documents to specify the target
	of a {hyperlink} which is often another HTML document
	(possibly stored on another computer).

	Here are some example URLs:

	 http://www.w3.org/default.html
	 http://www.acme.co.uk:8080/images/map.gif
	 http://www.foldoc.org/?Uniform+Resource+Locator
	 http://www.w3.org/default.html#Introduction
	 ftp://wuarchive.wustl.edu/mirrors/msdos/graphics/gifkit.zip
	 ftp://spy:secret@ftp.acme.com/pub/topsecret/weapon.tgz
	 mailto:fred@doc.ic.ac.uk
	 news:alt.hypertext
	 telnet://dra.com

	The part before the first colon specifies the access scheme or
	{protocol}.  Commonly implemented schemes include: {ftp},
	{http} (World-Wide Web), {gopher} or {WAIS}.  The "file"
	scheme should only be used to refer to a file on the same
	host.  Other less commonly used schemes include {news},
	{telnet} or mailto ({e-mail}).

	The part after the colon is interpreted according to the
	access scheme.  In general, two slashes after the colon
	introduce a {hostname} (host:port is also valid, or for {FTP}
	user:passwd@host or user@host).  The {port} number is usually
	omitted and defaults to the standard port for the scheme,
	e.g. port 80 for HTTP.

	For an HTTP or FTP URL the next part is a {pathname} which is
	usually related to the pathname of a file on the server.  The
	file can contain any type of data but only certain types are
	interpreted directly by most {browsers}.  These include {HTML}
	and images in {gif} or {jpeg} format.  The file's type is
	given by a {MIME} type in the HTTP headers returned by the
	server, e.g. "text/html", "image/gif", and is usually also
	indicated by its {filename extension}.  A file whose type is
	not recognised directly by the browser may be passed to an
	external "viewer" {application}, e.g. a sound player.

	The last (optional) part of the URL may be a query string
	preceded by "?" or a "fragment identifier" preceded by "#".
	The later indicates a particular position within the specified
	document.

	Only alphanumerics, reserved characters (:/?#"<>%+) used for
	their reserved purposes and "$", "-", "_", ".", "&", "+" are
	safe and may be transmitted unencoded.  Other characters are
	encoded as a "%" followed by two {hexadecimal} digits.  Space
	may also be encoded as "+".  Standard {SGML} "&<name>;"
	character entity encodings (e.g. "&eacute;") are also accepted
	when URLs are embedded in HTML.  The terminating semicolon may
	be omitted if &<name> is followed by a non-letter character.

	{The authoritative W3C URL specification
	(http://www.w3.org/hypertext/WWW/Addressing/Addressing.html)}.

	(2000-02-17)

<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)

<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)

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)

<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)

<World-Wide Web> (CSS) An extension to {HTML} to allow styles,
	e.g. colour, {font}, size to be specified for certain elements
	of a {hypertext} document.  Style information can be included
	in-line in the HTML file or in a separate CSS file (which can
	then be easily shared by multiple HTML files).  Multiple
	levels of CSS can be used to allow selective overriding of
	styles.

	{Home (http://www.w3.org/Style/CSS/)}.

	(2000-07-26)

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)

<World-Wide Web, project> A {open source} {HTTP} server for
	{Unix}, {Windows NT}, and other {platforms}.  Apache was
	developed in early 1995, based on code and ideas found in the
	most popular HTTP server of the time, {NCSA httpd} 1.3.  It
	has since evolved to rival (and probably surpass) almost any
	other {Unix} based HTTP server in terms of functionality, and
	speed.  Since April 1996 Apache has been the most popular HTTP
	server on the {Internet}, in May 1999 it was running on 57% of
	all web servers.

	It features highly configurable error messages, {DBM}-based
	{authentication} {databases}, and {content negotiation}.

	Latest version: 1.3.9, as of 1999-10-27.

	{Home (http://www.apache.org/httpd.html)}.

	{FAQ (http://www.apache.org/docs/misc/FAQ.html)}.

	(1999-10-27)

1. <chat> {Unix}'s simple {talk} command and {protocol}.
	write has been largely superseded by {talk} and then {irc}.

	An enhancement, {RWP}, has been proposed.

	2. <tool> A simple {text editor} for {Windows}.

	(1998-04-28)

1. Not simulated.  Often used as a specific antonym to
	{virtual} in any of its jargon senses.

	2. <mathematics> {real number}.

	[{Jargon File}]

	(1997-03-12)

<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)

<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)

{system administration}

1. <jargon> Not visible, hidden; said of a system which
	functions in a manner not evident to the user.  For example,
	the {Domain Name System} transparently resolves a {fully
	qualified domain name} into an {Internet address} without the
	user being aware of it.

	Compare this to what {Donald Norman
	(http://www.atg.apple.com/Norman/)} calls "invisibility",
	which he illustrates from the user's point of view:

	"You use computers when you use many modern automobiles,
	microwave ovens, games, CD players and calculators.  You don't
	notice the computer because you think of yourself as doing the
	task, not as using the computer."  ["The Design of Everyday
	Things", New York, Doubleday, 1989, p. 185].

	2. <theory> Fully defined, known, predictable; said of a
	sub-system in which matters generally subject to volition or
	stochastic state change have been chosen, measured, or
	determined by the environment.  Thus for transparent systems,
	output is a known function of the inputs, and users can both
	predict the behaviour and depend upon it.

	(1996-06-04)

<theory> The meaning of a string in some language, as opposed
	to {syntax} which describes how symbols may be combined
	independent of their meaning.

	The semantics of a programming language is a function from
	programs to answers.  A program is a {closed term} and, in
	practical languages, an answer is a member of the syntactic
	category of values.  The two main kinds are {denotational
	semantics} and {operational semantics}.

	(1995-06-21)