<programming> An {object} adhering to a {component
	architecture}.

	(1997-11-20)

<operating system> A {directory} in the sense of a collection
	of computer {files}.  The term is more common in systems such
	as the {Macintosh} or {Windows 95} which have a {graphical
	user interface} and provide a graphical {file browser} in
	which directories are traditionally depicted as folders (like
	small briefcases).

	(1997-03-20)

<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)

<storage> A {byte}, {word} or other small unit of storage
	space in a computer's {main memory} that is identified by its
	starting {address} (and size).

	(1999-04-19)

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)

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)

(From the technical term "logical device", wherein a physical
	device is referred to by an arbitrary "logical" name) Having
	the role of.  If a person (say, Les Earnest at SAIL) who had
	long held a certain post left and were replaced, the
	replacement would for a while be known as the "logical" Les
	Earnest.  (This does not imply any judgment on the
	replacement).

	Compare {virtual}.

	At Stanford, "logical" compass directions denote a coordinate
	system in which "logical north" is toward San Francisco,
	"logical west" is toward the ocean, etc., even though logical
	north varies between physical (true) north near San Francisco
	and physical west near San Jose.  (The best rule of thumb here
	is that, by definition, El Camino Real always runs logical
	north-and-south.)  In giving directions, one might say: "To
	get to Rincon Tarasco restaurant, get onto {El Camino Bignum}
	going logical north."  Using the word "logical" helps to
	prevent the recipient from worrying about that the fact that
	the sun is setting almost directly in front of him.  The
	concept is reinforced by North American highways which are
	almost, but not quite, consistently labelled with logical
	rather than physical directions.

	A similar situation exists at MIT: Route 128 (famous for the
	electronics industry that has grown up along it) is a
	3-quarters circle surrounding Boston at a radius of 10 miles,
	terminating near the coastline at each end.  It would be most
	precise to describe the two directions along this highway as
	"clockwise" and "counterclockwise", but the road signs all say
	"north" and "south", respectively.  A hacker might describe
	these directions as "logical north" and "logical south", to
	indicate that they are conventional directions not
	corresponding to the usual denotation for those words.  (If
	you went logical south along the entire length of route 128,
	you would start out going northwest, curve around to the
	south, and finish headed due east, passing along one infamous
	stretch of pavement that is simultaneously route 128 south and
	Interstate 93 north, and is signed as such!)

	[{Jargon File}]

	(1995-01-24)

1. A {cathode-ray tube} and associated electronics connected
	to a computer's video output.  A monitor may be either
	{monochrome} (black and white) or colour ({RGB}).  Colour
	monitors may show either digital colour (each of the red,
	green and blue signals may be either on or off, giving eight
	possible colours: black, white, red, green, blue, cyan,
	magenta and yellow) or analog colour (red, green and blue
	signals are continuously variable allowing any combination to
	be displayed).  Digital monitors are sometimes known as {TTL}
	because the voltages on the red, green and blue inputs are
	compatible with TTL logic chips.

	See also {gamut}, {multisync}, {visual display unit}.

	2. A programming language construct which encapsulates
	variables, access procedures and initialisation code within an
	abstract data type.  The monitor's variable may only be
	accessed via its access procedures and only one process may be
	actively accessing the monitor at any one time.  The access
	procedures are {critical sections}.  A monitor may have a
	queue of processes which are waiting to access it.

	3. A hardware device that measures electrical events such as
	pulses or voltage levels in a digital computer.

	4. To oversee a program during execution.  For example, the
	monitor function in the {Unix} {C} library enables profiling
	of a certain range of code addresses.  A histogram is produced
	showing how often the {program counter} was found to be at
	each position and how often each profiled function was called.

	{Unix} {man} page: monitor(3).

	5. A control program within the {operating system} that
	manages the allocation of system resources to active
	programs.

	6. A program that measures software performance.

1. A change to a product which is intended to make it better
	in some way, e.g. new functions, faster, or occasionally more
	compatible with other systems.  Enhancements to {hardware}
	components, especially {integrated circuits} often mean they
	are smaller and less demanding of resources.  Sadly, this is
	almost never true of {software} enhancements.

	2. {Marketroid}-speak for a {bug fix}.  This abuse of language
	is a popular and time-tested way to turn incompetence into
	increased revenue.  A hacker being ironic would instead call
	the fix a {feature}, or perhaps save some effort by declaring
	"{That's not a bug, that's a feature!}".

	[{Jargon File}]

	(1998-04-04)

<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)