1. <mathematics> An {edge} in a {tree}.

	2. <programming> A {jump}.

	(1998-11-14)

<file system> A node in a hierarchical {file system} which
	contains zero or more other nodes - generally, {files} or
	other directories.

	Compare {folder}.

	(1997-04-10)

<programming> (Sometimes "var" /veir/ or /var/) A named memory
	location in which a program can store intermediate results and
	from which it can read it them.  Each {programming language}
	has different rules about how variables can be named, typed,
	and used.  Typically, a value is "assigned" to a variable in
	an {assignment} statement.  The value is obtained by
	evaluating an expression and then stored in the variable.  For
	example, the assignment

		x = y + 1

	means "add one to y and store the result in x".  This may look
	like a mathematical equation but the mathematical equality is
	only true in the program until the value of x or y changes.
	Furthermore, statements like

		x = x + 1

	are common.  This means "add one to x", which only makes sense
	as a state changing operation, not as a mathematical equality.

	The simplest form of variable corresponds to a single-{word}
	of {memory} or a {CPU} {register} and an assignment to a
	{load} or {store} {machine code} operation.

	A variable is usually defined to have a {type}, which never
	changes, and which defines the set of values the variable can
	hold.  A type may specify a single ("atomic") value or a
	collection ("aggregate") of values of the same or different
	types.  A common aggregate type is the {array} - a set of
	values, one of which can be selected by supplying a numerical
	{index}.

	Languages may be {untyped}, {weakly typed}, {strongly typed},
	or some combination.  {Object-oriented programming} languages
	extend this to {object} types or {classes}.

	A variable's {scope} is the region of the program source
	within which it represents a certain thing.  Scoping rules are
	also highly language dependent but most serious languages
	support both {local variables} and {global variables}.
	{Subroutine} and {function} {formal arguments} are special
	variables which are set automatically by the language runtime
	on entry to the subroutine.

	In a {functional programming} language, a variable's value
	never changes and change of state is handled as recursion over
	lists of values.

	(2004-11-16)

<programming> (Or "parameter") A name in a {function} or
	{subroutine} definition that is replaced by, or bound to, the
	corresponding {actual argument} when the function or
	subroutine is called.  In many languages formal arguments
	behave like {local variables} which get initialised on entry.

	See: {argument}.

	(2002-07-02)

1. <operating system> The {Unix} {superuser} account (with
	user name "root" and user ID 0) that overrides file
	permissions.  The term {avatar} is also used.  By extension,
	the privileged system-maintenance login on any {operating
	system}.

	See {root mode}, {go root}, {wheel}.

	[{Jargon File}]

	(1994-10-27)

	2. <operating system> {root directory}.

	(1996-11-21)

	3. <data> {root node}.

	(1998-11-14)

(Or "primitive") A built-in function or operator is one
	provided by the lowest level of a language implementation.
	This usually means it is not possible (or efficient) to
	express it in the language itself.  Typical examples are the
	basic arithmetic and {Boolean} operators (in {C} syntax: +, -,
	*, /, %, !, &&, ||), bit manipulation operators (~, &, |, ^)
	and I/O primitives.  Other common functions may be provided in
	libraries but are not built-in if they are written in the
	language being implemented.

	(1995-02-14)

<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)

See {followup}.

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)

<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. <programming> An independent piece of {software} which
	forms part of one or more larger {programs}.  Different
	languages have different concepts of a module but there are
	several common ideas.

	Modules are usually compiled seperately (in compiled
	languages) and provide an {abstraction} or information hiding
	mechanism so that a module's implementation can be changed
	without requiring any change to other modules.  In this
	respect they are similar to {objects} in an {object-oriented
	language}, though a module may contain many {procedures}
	and/or {functions} which would correspond to many objects.

	A module often has its own {name space} for {identifiers} so
	the same identifier may be used to mean different things in
	different modules.

	[Difference from {package}?].

	2. <hardware> An independent assembly of electronic components
	with some distinct function, e.g. a RAM module consisting of
	several RAM chips mounted on a small circuit board.

	(1997-10-27)

<character> (Or "ctrl", "^") One (or a pair) of {modifier
	keys} found on all modern {keyboards}.  If the control key is
	held down while pressing and releasing certain other keys then
	a "{control character}" is generated, e.g. holding control and
	hitting "A" generates control-A ({ASCII} code 1).  The ASCII
	code for the control character is generally 64 less than that
	for the unmodified character.

	The control key does not generate any character on its own but
	most modern keyboards and {operating systems} allow a program
	to tell whether each of the individual keys on the keyboard
	(including modifier keys) is pressed at any time.

	Control characters mostly have some kind of "non-printing"
	effect on the output such as ringing the bell (Control-G) or
	advancing to the next line (Control-J).  Most have alternative
	names suggesting these functions (Bell, Line Feed, etc.).

	See {ASCII character table}.

	(1997-07-10)

1. <programming> {Speech Application Programming Interface}.

	2. <programming> {Scheduling Application Programming
	Interface}.

	3. <networking> {Service Access Point Identifier}.

	(1996-10-03)

<jargon, architecture> (Via the technical term {virtual
	memory}, probably from the term "virtual image" in optics)
	1. Common alternative to {logical}; often used to refer to the
	artificial objects (like addressable {virtual memory} larger
	than physical memory) created by a computer system to help the
	system control access to shared resources.

	2. Simulated; performing the functions of something that isn't
	really there.  An imaginative child's doll may be a virtual
	playmate.

	Opposite of {real} or physical.

	[{Jargon File}]

	(1994-11-30)

1. <networking> A computer connected to a {network}.

	The term {node} includes devices such as routers and printers
	which would not normally be called "hosts".

	2. <communications> A computer to which one connects using a
	{terminal emulator}.

	(1995-02-16)

<theory> The least defined element in a given {domain}.

	Often used to represent a non-terminating computation.

	(In {LaTeX}, bottom is written as {\perp}, sometimes with the
	domain as a subscript).

	(1997-01-07)

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)

<computer> A machine that can be programmed to manipulate
	symbols.  Computers can perform complex and repetitive
	procedures quickly, precisely and reliably and can quickly
	store and retrieve large amounts of data.

	The physical components from which a computer is constructed
	(electronic circuits and input/output devices) are known as
	"{hardware}".  Most computers have four types of hardware
	component: CPU, input, output and memory.  The CPU ({central
	processing unit}) executes programs ("{software}") which tell
	the computer what to do.  Input and output (I/O) devices allow
	the computer to communicate with the user and the outside
	world.  There are several kinds of memory - fast, expensive,
	short term memory (e.g. {RAM}) to hold intermediate results,
	and slower, cheaper, long-term memory (e.g. {magnetic disk} and
	{magnetic tape}) to hold programs and data between jobs.

	See also {analogue computer}.

	(1995-03-10)