<protocol> (UDP) {Internet} {standard} {network layer},
	{transport layer} and {session layer} {protocols} which
	provide simple but {unreliable} {datagram} services.  UDP is
	defined in {STD 6}, {RFC 768}.  It adds a {checksum} and
	additional process-to-process addressing information [to
	what?].  UDP is a {connectionless protocol} which, like {TCP},
	is layered on top of {IP}.

	UDP neither guarantees delivery nor does it require a
	connection.  As a result it is lightweight and efficient, but
	all error processing and retransmission must be taken care of
	by the {application program}.

	{Unix manual page}: udp(4).

	[Postel, Jon, User Datagram Protocol, RFC 768, Network
	Information Center, SRI International, Menlo Park, Calif.,
	August 1980].

	(1998-02-11)

1. {application program}.

	2. {function application}.

The unit of data sent across a {network}.  "Packet" is a
	generic term used to describe a unit of data at any layer of
	the {OSI} {protocol stack}, but it is most correctly used to
	describe {application layer} data units ("{application
	protocol data unit}", APDU).

	See also {datagram}, {frame}.

	(1994-11-30)

<standard> Standards are necessary for {interworking},
	{portability}, and {reusability}.  They may be {de facto
	standards} for various communities, or officially recognised
	national or international standards.

	{Andrew Tanenbaum}, in his Computer Networks book, once said,
	"The nice thing about standards is that there are so many of
	them to choose from", a reference to the fact that competing
	standards become a source of confusion, division,
	obsolescence, and duplication of effort instead of an
	enhancement to the usefulness of products.

	Some bodies concerned in one way or another with computing
	standards are {IAB} ({RFC} and {STD}), {ISO}, {ANSI}, {DoD},
	{ECMA}, {IEEE}, {IETF}, {OSF}, {W3C}.

	(1999-07-06)

<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. 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.

1. (Or "finite", "isolated") In {domain theory}, an element d
	of a {cpo} D is compact if and only if, for any {chain} S, a
	subset of D,

		d <= lub S  =>  there exists s in S such that d <= s.

	I.e. you always reach d (or better) after a finite number of
	steps up the chain.

	("<=" is written in {LaTeX} as {\sqsubseteq}).

	[{Jargon File}]

	(1995-01-13)

	2. Of a design, describes the valuable property that it can
	all be apprehended at once in one's head.  This generally
	means the thing created from the design can be used with
	greater facility and fewer errors than an equivalent tool that
	is not compact.  Compactness does not imply triviality or lack
	of power; for example, {C} is compact and {Fortran} is not,
	but C is more powerful than Fortran.  Designs become
	non-compact through accreting {features} and {cruft} that
	don't merge cleanly into the overall design scheme (thus, some
	fans of {Classic C} maintain that {ANSI C} is no longer
	compact).

	(1995-01-13)

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)

<programming> Saving the current state of a program and its
	data, including intermediate results, to disk or other
	{non-volatile storage}, so that if interrupted the program
	could be restarted at the point at which the last checkpoint
	occurred.

	This facility came into popular use in {mainframe} {operating
	systemss} such as {OS/360} in which programs frequently ran
	for longer than the mean time between system failures.  If a
	program run fails because of some event beyond the program's
	control (e.g. hardware or {operating system} failure) then the
	processor time invested before the checkpoint will not have
	been wasted.

	(1995-02-07)

To check the status of an input line, sensor, or memory
	location to see if a particular external event has been
	registered.

	Contrast {interrupt}.

	[{Jargon File}]

	(1995-01-31)

<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)

<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)

<character> The space character, {ASCII} 32.

	See {octal forty}.

<messaging> 1. {electronic mail}.

	2. The {Berkeley Unix} program for composing and reading
	{electronic mail}.  It normally uses {sendmail} to handle
	delivery.

	{Unix manual page}: mail(1)

	(1997-12-03)