<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)

<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. <programming> A common name for the {integer} data type.
	In {C} for example, it means a (signed) integer of the
	computer's native {word length}.

	2. <networking> The {top-level domain} for international
	organisations.

	(1999-01-26)

1. <theory> In {domain theory}, the sum A + B of two {domains}
	contains all elements of both domains, modified to indicate
	which part of the union they come from, plus a new {bottom}
	element.  There are two constructor functions associated with
	the sum:

		inA : A -> A+B       inB : B -> A+B
		inA(a) = (0,a)	     inB(b) = (1,b)

	and a disassembly operation:

		case d of {isA(x) -> E1; isB(x) -> E2}

	This can be generalised to arbitrary numbers of domains.

	See also {smash sum}, {disjoint union}.

	2. <tool> A {Unix} utility to calculate a 16-bit {checksum} of
	the data in a file.  It also displays the size of the file,
	either in {kilobytes} or in 512-byte blocks.  The checksum may
	differ on machines with 16-bit and 32-bit ints.

	{Unix manual page}: sum(1).

	(1995-03-16)

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)

<architecture> {Data} transferred from a computer system to
	the outside world via some kind of {output device}.

	Opposite: {input}.

	(1997-04-28)

<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)

Common term for "computer", usually when considered at the
	hardware level.  The {Turing Machine}, an early example of
	this usage, was however neither hardware nor software, but
	only an idea.

	[Earlier use?]

	(1995-02-15)

1. <language, programming> {programming language}.

	2. <human language> {natural language}.

	(1998-09-07)

Loosely used to mean "in accordance with all the relevant
	rules", especially in connection with some set of constraints
	defined by software.  "The older =+ alternate for += is no
	longer legal syntax in ANSI C."  "This parser processes each
	line of legal input the moment it sees the trailing linefeed."
	Hackers often model their work as a sort of game played with
	the environment in which the objective is to maneuver through
	the thicket of "natural laws" to achieve a desired objective.
	Their use of "legal" is flavoured as much by this game-playing
	sense as by the more conventional one having to do with courts
	and lawyers.  Compare {language lawyer}, {legalese}.

	[{Jargon File}]

1. <programming> A variable or quantity that can take on one
	of two values; a bit, particularly one that is used to
	indicate one of two outcomes or is used to control which of
	two things is to be done.  "This flag controls whether to
	clear the screen before printing the message."  "The program
	status word contains several flag bits."  See also {hidden
	flag}, {mode bit}.

	2. {command line option}.

	[{Jargon File}]

	(1998-05-02)

<architecture> A {virtual machine} implementation approach,
	used to speed up execution of {byte-code} programs.  To
	execute a program unit such as a {method} or a {function}, the
	virtual machine compiles its bytecodes into (hardware) machine
	code.  The translated code is also placed in a cache, so that
	next time that unit's machine code can be executed
	immediately, without repeating the translation.

	This technique was pioneered by the commercial {Smalltalk}
	implementation currently known as {VisualWorks}, in the early
	1980s.  Currently it is also used by some implementations of
	the {Java Virtual Machine} under the name {JIT} (Just In Time
	compilation).

	[Peter L. Deutsch and Alan Schiffman. "Efficient
	Implementation of the Smalltalk-80 System", 11th Annual
	Symposium on Principles of Programming Languages, Jan 1984,
	pp. 297-302].

	(2002-04-15)

/knooth/ 1. {Donald Knuth}.

	2. ["The Art of Computer Programming", Donald E. Knuth]
	Mythically, the reference that answers all questions about
	data structures or algorithms.  A safe answer when you do not
	know: "I think you can find that in Knuth."

	Contrast {literature}.  See also {bible}.

	[{Jargon File}]

An error condition that changes the normal {flow of control}
	in a program.  An exception may be generated ("raised") by
	{hardware} or {software}.  Hardware exceptions include
	{reset}, {interrupt} or a signal from a {memory management
	unit}.  Exceptions may be generated by the {arithmetic logic
	unit} or {floating-point unit} for numerical errors such as
	divide by zero, {overflow} or {underflow} or {instruction
	decoding} errors such as privileged, reserved, {trap} or
	undefined instructions.  Software exceptions are even more
	varied and the term could be applied to any kind of error
	checking which alters the normal behaviour of the program.

	(1994-10-31)

<storage> These days, usually used synonymously with {Random
	Access Memory} or {Read-Only Memory}, but in the general sense
	it can be any device that can hold {data} in
	{machine-readable} format.

	(1996-05-25)