1. <philosophy, mathematics> A branch of philosophy and
	mathematics that deals with the formal principles, methods and
	criteria of validity of {inference}, reasoning and
	{knowledge}.

	Logic is concerned with what is true and how we can know
	whether something is true.  This involves the formalisation of
	logical arguments and {proofs} in terms of symbols
	representing {propositions} and {logical connectives}.  The
	meanings of these logical connectives are expressed by a set
	of rules which are assumed to be self-evident.

	{Boolean algebra} deals with the basic operations of truth
	values: AND, OR, NOT and combinations thereof.  {Predicate
	logic} extends this with existential and universal
	{quantifiers} and symbols standing for {predicates} which may
	depend on variables.  The rules of {natural deduction}
	describe how we may proceed from valid premises to valid
	conclusions, where the premises and conclusions are
	expressions in {predicate logic}.

	Symbolic logic uses a {meta-language} concerned with truth,
	which may or may not have a corresponding expression in the
	world of objects called existance.  In symbolic logic,
	arguments and {proofs} are made in terms of symbols
	representing {propositions} and {logical connectives}.  The
	meanings of these begin with a set of rules or {primitives}
	which are assumed to be self-evident.  Fortunately, even from
	vague primitives, functions can be defined with precise
	meaning.

	{Boolean logic} deals with the basic operations of {truth
	values}: AND, OR, NOT and combinations thereof.  {Predicate
	logic} extends this with {existential quantifiers} and
	{universal quantifiers} which introduce {bound variables}
	ranging over {finite} sets; the {predicate} itself takes on
	only the values true and false.  Deduction describes how we
	may proceed from valid {premises} to valid conclusions, where
	these are expressions in {predicate logic}.

	Carnap used the phrase "rational reconstruction" to describe
	the logical analysis of thought.  Thus logic is less concerned
	with how thought does proceed, which is considered the realm
	of psychology, and more with how it should proceed to discover
	truth.  It is the touchstone of the results of thinking, but
	neither its regulator nor a motive for its practice.

	See also fuzzy logic, logic programming, arithmetic and logic unit,
	first-order logic,

	See also {Boolean logic}, {fuzzy logic}, {logic programming},
	{first-order logic}, {logic bomb}, {combinatory logic},
	{higher-order logic}, {intuitionistic logic}, {equational
	logic}, {modal logic}, {linear logic}, {paradox}.

	2. <electronics> {Boolean} logic circuits.

	See also {arithmetic and logic unit}, {asynchronous logic},
	{TTL}.

	(1995-03-17)

1. <hardware> {monitor}.

	2. <language> A vector of pointers to {activation records}.
	The Nth element points to the activation record containing
	variables declared at {lexical depth} N.  This allows faster
	access to variables from outer {scopes} than the alternative
	of linked activation records (but most variable accesses are
	either local or global or occasionally to the immediately
	enclosing scope).  Displays were used in some {ALGOL}
	implementations.

	(1996-02-22)

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)

<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)

<convention, data> A string unique to a time duration of 24
	hours between 2 successive midnights defined by the local time
	zone.  The specific representation of a date will depend on
	which calendar convention is in force; e.g., Gregorian,
	Islamic, Japanese, Chinese, Hebrew etc. as well as local
	ordering conventions such as UK: day/month/year, US:
	month/day/year.

	Inputting and outputting dates on computers is greatly
	complicated by these {localisation} issues which is why they
	tend to operate on dates internally in some unified form such
	as seconds past midnight at the start of the first of January
	1970.

	Many software and hardware representations of dates allow only
	two digits for the year, leading to the {year 2000} problem.

	{Unix manual page}: date(1), ctime(3).

	(1997-07-11)

<World-Wide Web> (Or "website") Any computer on the
	{Internet} running a {World-Wide Web} {server} process.  A
	particular website is usually identified by the {hostname}
	part of a {URL}.  Multiple hostnames may actually map to the
	same computer in which case they are known as "{virtual
	servers}".

	(2005-07-12)

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)

1. <architecture> {cache hit}.

	2. <World-Wide Web> A request to a {web server} from a {web
	browser} or other {client} (e.g. a {robot}).

	The number of hits on a server may be important for
	determining advertising revenue.

	In the course of loading a single {web page}, a browser may
	hit a web server many times e.g. to retrieve the page itself
	and each {image} on the page.  In contrast, caching by
	browsers and {web proxies} reduces the number of hits on the
	server because some requests are satisfied from the cache.

	3. <jargon> To press and release a key on the keyboard.  Some
	prefer the less aggressive "tap".

	(2000-02-20)

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)

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}.

<company> The biggest supplier of {operating systems} and
	other software for {IBM PC} compatibles.  Software products
	include {MS-DOS}, {Microsoft Windows}, {Windows NT},
	{Microsoft Access}, {LAN Manager}, {MS Client}, {SQL Server},
	{Open Data Base Connectivity} (ODBC), {MS Mail}, and {SNA
	Server} for Windows NT.

	Microsoft was founded as "Micro-soft" in 1975 by {Bill Gates}
	(now CEO) and his high school pal Paul Allen.  Their first
	product was a version of {BASIC} for the new {Altair} computer
	[which one?].  In 1980, {IBM} chose Microsoft to supply the
	{operating system} for the {IBM PC}.

	On the UK television program "The Net" in May 1994, {Bill
	Gates} said he was betting his company on the {information
	highway}".

	Quarterly sales $1293M, profits $362M (Aug 1994).

	{Home (http://www.microsoft.com/)}.
	{(ftp://ftp.microsoft.com/)}.

	{Interesting Info and Other Microsoft WWW Servers
	(http://www-drg.microsoft.com/devinfo.htm)}.

	{Microsoft Windows Developer Information
	(http://www-drg.microsoft.com/devinfo.htm)}.

	{Microsoft Research Group Information
	(http://www.research.microsoft.com)}.

	{Win_News
	(http://www.microsoft.com/chicago/ms-www/ms-intro.htm)}.
	maintained by the Personal Operating Systems Division to
	distribute information on {Microsoft Windows}, {MS-DOS} and
	{Windows 95}.

	(1998-11-06)

<product> {Microsoft}'s bundles of {productivity tools}
	including {Microsoft Word}, {Microsoft Excel}, {Microsoft
	Powerpoint}, {Microsoft Outlook}, {Microsoft Access},
	{Microsoft Publisher}, {Microsoft Front Page}, {Microsoft Team
	Manager}, {Microsoft Project}, {Microsoft Schedule+},
	{Microsoft Internet Explorer}, {Small Business Financial
	Manager}, {Automap Streets Plus}.

	Editions of Office include {Microsoft Office Professional
	Edition}, {Microsoft Office Standard Edition}, {Microsoft
	Office Small Business Edition}, {Microsoft Office Developer
	Edition}.  Different editions contain different subsets of the
	above applications.

	Current version, as of 2004-08-30: Office 2003.

	{Home (http://www.microsoft.com/office)}.

	(2004-08-30)

<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)

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)

<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)

<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. <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)

<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)

<software> A program by {Richard Stallman} to discover
	properties of the current {platform} and to set up {make} to
	compile and install {gcc}.

	{Cygnus configure} was a similar system developed by
	K. Richard Pixley in collaboration with Richard Stallman.
	In 1994, David MacKenzie and others modified {autoconf} to
	incorporate all the features of Cygnus configure and many
	{GNU} programs, including gcc now use autoconf.

	{Metaconfig} is a similar program used in building {Perl}.

	{(http://www.airs.com/ian/configure)}.

	(2005-04-15)

1. <programming, operating system> A simple item of data that
	identifies a resource.  For example, a {Unix} file handle
	identifies an open file and associated data such as whether it
	was opened for read or write and the current read/write
	position.  On the {Macintosh}, a handle is a pointer to a
	pointer to some dynamically-allocated memory.  The extra level
	of indirection allows on-the-fly {memory compaction} or
	{garbage collection} without invalidating application program
	references to the allocated memory.

	2. <jargon> An alias used intended to conceal a user's true
	identity in an electronic message.  The term is common on
	Citizen's Band and other amateur radio but, in that context
	usually means the user's real name as {FCC} rules forbid
	concealing one's identity.

	Use of grandiose handles is characteristic of {crackers},
	{weenies}, {spods}, and other lower forms of network life;
	true hackers travel on their own reputations.

	Compare {nick}.

	[{Jargon File}]

	(2004-07-20)

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)

<file format, multimedia> (MIME) A {standard} for multi-part,
	{multimedia} {electronic mail} messages and {World-Wide Web}
	{hypertext} documents on the {Internet}.  MIME provides the
	ability to transfer non-textual data, such as graphics,
	{audio} and fax.  It is defined in {RFC 2045}, {RFC 2046},
	{RFC 2047}, {RFC 2048}, {RFC 2049}, and {BCP0013}.  It uses
	{mimencode} to encode binary data into {base 64} using a
	subset of {ASCII}.

	{FAQ
	(http://www.cis.ohio-state.edu/hypertext/faq/usenet/mail/mime-faq/top.html)}.

	(1995-04-04)