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.

<networking> The {Berkeley Unix} mechansim for creating a
	virtual connection between processes.  Sockets interface
	{Unix}'s {standard I/O} with its {network} communication
	facilities.  They can be of two types, stream (bi-directional)
	or {datagram} (fixed length destination-addressed messages).
	The socket library function socket() creates a communications
	end-point or socket and returns a {file descriptor} with which
	to access that socket.  The socket has associated with it a
	socket address, consisting of a {port} number and the local
	host's network address.

	{Unix manual page}: socket(2).

	(1995-01-31)

1. {application program}.

	2. {function application}.

1. To prepare to read or write a file.  This usually involves
	checking whether the file already exists and that the user has
	the necessary authorisation to read or write it.  The result
	of a successful open is usually some kind of {capability}
	(e.g. a {Unix} {file descriptor}) - a token that the user
	passes back to the system in order to access the file without
	further checks and finally to close the file.

	2. Abbreviation for "open (or left) parenthesis" - used when
	necessary to eliminate oral ambiguity.  To read aloud the LISP
	form (DEFUN FOO (X) (PLUS X 1)) one might say: "Open defun
	foo, open eks close, open, plus eks one, close close."

	3. Non-proprietary.  An open {standard} is one which can be
	used without payment.

	[{Jargon File}]

	(1995-01-31)

1. <mathematics> A {set} containing a certain number of
	objects selected from another set.

	The number of combinations of r objects chosen from a set of n
	is

		n C r = n! / ((n-r)! r!)

	where "n C r" is normally with n and r as subscripts or as n
	above r in parentheses.

	See also {permutation}.

	2. <reduction> In the theory of {combinators}, a combination
	denotes an expression in which {function application} is the
	only operation.

	(1995-04-10)

<data, data processing, jargon> /day't*/ (Or "raw data")
	Numbers, {characters}, {images}, or other method of recording,
	in a form which can be assessed by a human or (especially)
	input into a {computer}, stored and {processed} there, or
	transmitted on some {digital channel}.  Computers nearly
	always represent data in {binary}.

	Data on its own has no meaning, only when interpreted by some
	kind of {data processing system} does it take on meaning and
	become {information}.

	People or computers can find patterns in data to perceive
	information, and information can be used to enhance
	{knowledge}.  Since knowledge is prerequisite to wisdom, we
	always want more data and information.  But, as modern
	societies verge on {information overload}, we especially need
	better ways to find patterns.

	1234567.89 is data.

	"Your bank balance has jumped 8087% to $1234567.89" is
	information.

	"Nobody owes me that much money" is knowledge.

	"I'd better talk to the bank before I spend it, because of
	what has happened to other people" is wisdom.

	(1999-04-30)

(Or "REDL") A language proposed by {Intermetrics} to meet the
	{Ironman} requirements which led to {Ada}.

	["On the RED Language Submitted to the DoD", E.W. Dijkstra,
	SIGPLAN Notices 13(10):27 (Oct 1978)].

	["RED Language Reference Manual", J. Nestor and M. van Deusen,
	Intermetrics 1979].

	(1995-01-19)

<programming, operating system> (I/O) Communication between a
	computer and its users, its storage devices, other computers
	(via a {network}) or the outside world.  The devices the
	computer uses to do this are called "{peripherals}".  What
	actually counts as I/O depends on what level of detail you are
	considering, e.g. communication between processors would not
	be considered I/O when considering a {multiprocessor} as a
	single system.

	Important aspects of I/O are {throughput}, {latency}, and
	whether the communications is {synchronous} or {asynchronous}
	(using some kind of {buffer}).

	(2003-12-04)

1. An area of memory used for storing messages.  Typically, a
	buffer will have other attributes such as an input pointer
	(where new data will be written into the buffer), and output
	pointer (where the next item will be read from) and/or a count
	of the space used or free.  Buffers are used to decouple
	processes so that the reader and writer may operate at
	different speeds or on different sized blocks of data.

	There are many different algorithms for using buffers, e.g.
	first-in first-out (FIFO or shelf), last-in first-out (LIFO or
	stack), double buffering (allowing one buffer to be read while
	the other is being written), cyclic buffer (reading or writing
	past the end wraps around to the beginning).

	2. An electronic device to provide compatibility between two
	signals, e.g. changing voltage levels or current capability.

<process> The approach that engineering (and some other)
	disciplines use to specify how to create or do something.  A
	successful design must satisfies a (perhaps informal)
	{functional specification} (do what it was designed to do);
	conforms to the limitations of the target medium (it is
	possible to implement); meets implicit or explicit
	requirements on performance and resource usage (it is
	efficient enough).

	A design may also have to satisfy restrictions on the design
	process itself, such as its length or cost, or the tools
	available for doing the design.

	In the {software life-cycle}, design follows {requirements
	analysis} and is followed by implementation.

	["Object-Oriented Analysis and Design with Applications", 2nd
	ed., Grady Booch].

	(1996-12-08)

<data processing, signal processing> Performing some
	predefined sequence of operations on an input to produce an
	output or change of internal state; activity specifically
	involving the computer's {CPU}.

	The term is often qualified: "{data processing}" treats
	{digital} data, "{signal processing}" treats {analog} data
	(possibly in digital form), "{word processing}" takes in typed
	human language input and produces digital documents, {image
	processing} transforms digital {images}.

	(2003-10-23)

See {followup}.

1. <networking> {e-mail address}.

	2. <networking> {Internet address}.

	3. <networking> {MAC address}.

	4. <storage, programming> An unsigned integer used to select
	one fundamental element of storage, usually known as a {word}
	from a computer's {main memory} or other storage device.  The
	{CPU} outputs addresses on its {address bus} which may be
	connected to an {address decoder}, {cache controller}, {memory
	management unit}, and other devices.

	While from a hardware point of view an address is indeed an
	integer most {strongly typed} programming languages disallow
	mixing integers and addresses, and indeed addresses of
	different data types.  This is a fine example for {syntactic
	salt}: the compiler could work without it but makes writing
	bad programs more difficult.

	(1997-07-01)

<programming> A program like {Unix}'s "split" which breaks an
	input file into parts, usually of a pre-set size, e.g. the
	maximum size that can fit on a {floppy}.  The parts can then
	be assembled with a {dechunker}, which is usually just the
	chunker in a different mode.

	(1998-12-15)

1. <operating system> {device driver}.

	2. <programming> The {main loop} of an event-processing
	program; the code that gets commands and dispatches them for
	execution.

	3. <tool> In the {TeX} world and the computerised typesetting
	world in general, a program that translates some
	device-independent or other common format to something a real
	device can actually understand.

	[{Jargon File}]

<networking, protocol> (TCP) The most common {transport layer}
	{protocol} used on {Ethernet} and the {Internet}.  It was
	developed by {DARPA}.

	TCP is the {connection-oriented} protocol built on top of
	{Internet Protocol} (IP) and is nearly always seen in the
	combination {TCP/IP} (TCP over IP).  It adds {reliable
	communication} and {flow-control} and provides {full-duplex},
	process-to-process connections.

	TCP is defined in {STD 7} and {RFC} 793.

	{User Datagram Protocol} is the other, connectionless,
	protocol that runs on top of IP.

	(2001-06-14)

<language, architecture> (JVM) A specification for software
	which interprets {Java} programs that have been compiled into
	{byte-codes}, and usually stored in a ".class" file.  The JVM
	{instruction set} is {stack}-oriented, with variable
	instruction length.  Unlike some other instruction sets, the
	JVM's supports {object-oriented} programming directly by
	including instructions for object {method} invocation (similar
	to {subroutine} call in other instruction sets).

	The JVM itself is written in {C} and so can be {ported} to run
	on most {platforms}.  It needs {thread} support and {I/O} (for
	{dynamic class loading}).  The Java byte-code is independent
	of the platform.

	There are also some hardware implementations of the JVM.

	{Specification
	(http://www.javasoft.com/docs/books/vmspec/html/VMSpecTOC.doc.html)}.

	{Sun's Java chip
	(http://news.com/News/Item/0,4,9328,00.html)}.

	[Documentation?  Versions?]

	(2000-01-03)

That which surrounds, and gives meaning to, something else.

	<grammar> In a {grammar} it refers to the symbols before and
	after the symbol under consideration.  If the syntax of a
	symbol is independent of its context, the grammar is said to
	be {context-free}.

<programming> (JNI) A {native} programming interface for
	{Java} that allows Java code running inside a {Java Virtual
	Machine} to interoperate with {applications} and {libraries}
	written in other programming languages such as {C}, {C++} and
	{assembly language}.

	(1997-12-07)