<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)

<programming> The name given in {Smalltalk} and other
	{object-oriented languages} to a procedure or routine
	associated with one or more {classes}.  An {object} of a
	certain class knows how to perform actions, e.g. printing
	itself or creating a new instance of itself, rather than the
	function (e.g. printing) knowing how to handle different types
	of object.

	Different classes may define methods with the same name
	(i.e. methods may be {polymorphic}).  The term "method" is used
	both for a named operation, e.g. "PRINT" and also for the code
	which a specific class provides to perform tha
	t operation.

	Most methods operate on objects that are instances of a
	certain class.  Some object-oriented languages call these
	"object methods" to distinguish then from "{class methods}".

	In {Smalltalk}, a method is defined by giving its name,
	documentation, temporary local variables and a sequence of
	expressions separated by "."s.

	(2000-03-22)

<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)

<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)

<unit> (b) {binary} digit.

	The unit of information; the amount of information obtained by
	asking a yes-or-no question; a computational quantity that can
	take on one of two values, such as false and true or 0 and 1;
	the smallest unit of storage - sufficient to hold one bit.

	A bit is said to be "set" if its value is true or 1, and
	"reset" or "clear" if its value is false or 0.  One speaks of
	setting and clearing bits.  To {toggle} or "invert" a bit is
	to change it, either from 0 to 1 or from 1 to 0.

	The term "bit" first appeared in print in the computer-science
	sense in 1949, and seems to have been coined by the eminent
	statistician, {John Tukey}.  Tukey records that it evolved
	over a lunch table as a handier alternative to "bigit" or
	"binit".

	See also {flag}, {trit}, {mode bit}, {byte}, {word}.

	[{Jargon File}]

	(2002-01-22)

<electronics> The quantity of {charge} per unit time, measured
	in Amperes (Amps, A).  By historical convention, the sign of
	current is positive for currents flowing from positive to
	negative {potential}, but experience indicates that electrons
	are negatively charged and flow in the opposite direction.

	(1995-10-05)

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)

<programming, tool> A program that converts another program
	from some {source language} (or {programming language}) to
	{machine language} (object code).  Some compilers output
	{assembly language} which is then converted to {machine
	language} by a separate {assembler}.

	A compiler is distinguished from an assembler by the fact that
	each input statement does not, in general, correspond to a
	single machine instruction or fixed sequence of instructions.
	A compiler may support such features as automatic allocation
	of variables, arbitrary arithmetic expressions, control
	structures such as FOR and WHILE loops, variable {scope},
	input/ouput operations, {higher-order functions} and
	{portability} of source code.

	{AUTOCODER}, written in 1952, was possibly the first primitive
	compiler.  {Laning and Zierler}'s compiler, written in
	1953-1954, was possibly the first true working algebraic
	compiler.

	See also {byte-code compiler}, {native compiler}, {optimising
	compiler}.

	(1994-11-07)

A language proposed by Cii {Honeywell-Bull} to meet the DoD
	{Ironman} requirements which led to {Ada}.  This language won
	in 1979.

	["On the GREEN Language Submitted to the DoD", E.W. Dijkstra,
	SIGPLAN Notices 13(10):16-21 (Oct 1978)].

	(1994-12-02)

1. <unit> The standard metric prefixes used in the {Systme
	International d'Units} (SI) conventions for scientific
	measurement.

	Here are the SI magnifying prefixes, along with the
	corresponding binary interpretations in common use:

	 prefix abr decimal  binary

	 yocto-     1000^-8
	 zepto-     1000^-7
	 atto-      1000^-6
	 femto-  f  1000^-5
	 pico-   p  1000^-4
	 nano-   n  1000^-3
	 micro-  *  1000^-2          * Abbreviation: Greek mu
	 milli-  m  1000^-1

	 kilo- 	 k  1000^1  1024^1 = 2^10 = 1,024
	 mega- 	 M  1000^2  1024^2 = 2^20 = 1,048,576
	 giga- 	 G  1000^3  1024^3 = 2^30 = 1,073,741,824
	 tera- 	 T  1000^4  1024^4 = 2^40 = 1,099,511,627,776
	 peta- 	    1000^5  1024^5 = 2^50 = 1,125,899,906,842,624
	 exa-  	    1000^6  1024^6 = 2^60 = 1,152,921,504,606,846,976
	 zetta-     1000^7  1024^7 = 2^70 = 1,180,591,620,717,411,303,424
	 yotta-     1000^8  1024^8 = 2^80 = 1,208,925,819,614,629,174,706,176

	"Femto" and "atto" derive not from Greek but from Danish.

	The abbreviated forms of these prefixes are common in
	electronics and physics.

	When used with bytes of storage, these prefixes usually denote
	multiplication by powers of 1024 = 2^10 (K, M, and G are
	common in computing).  Thus "MB" stands for megabytes (2^20
	bytes).  This common practice goes against the edicts of the
	{BIPM} who deprecate the use of these prefixes for powers of
	two.  The formal SI prefix for 1000 is lower case "k"; some,
	including this dictionary, use this strictly, reserving upper
	case "K" for multiplication by 1024 (KB is thus "kilobytes").

	Also, in data transfer rates the prefixes stand for powers of
	ten so, for example, 28.8 kb/s means 28,800 bits per second.

	The unit is often dropped so one may talk of "a 40K salary"
	(40000 dollars) or "2 meg of disk space" (2*2^20 bytes).

	The accepted pronunciation of the initial G of "giga-" is
	hard, /gi'ga/.

	Confusing 1000 and 1024 (or other powers of 2 and 10 close in
	magnitude) - for example, describing a memory in units of 500K
	or 524K instead of 512K - is a sure sign of the {marketroid}.
	For example, 3.5" {microfloppies} are often described as
	storing "1.44 MB".  In fact, this is completely specious.  The
	correct size is 1440 KB = 1440 * 1024 = 1474560 bytes.  Alas,
	this point is probably lost on the world forever.

	In 1993, hacker Morgan Burke proposed, to general approval on
	{Usenet}, the following additional prefixes: groucho (10^-30),
	harpo (10^-27), harpi (10^27), grouchi (10^30).  This would
	leave the prefixes zeppo-, gummo-, and chico- available for
	future expansion.  Sadly, there is little immediate prospect
	that Mr. Burke's eminently sensible proposal will be ratified.

	2. <language> Related to the {prefix notation}.

	(2003-05-06)

<company> (IBM) The best known American computer manufacturer,
	founded by Thomas J. Watson (born 1874-02-17), known as "Big
	Blue" after the colour of its logo.  IBM makes everything from
	{mainframes} to {personal computers} (PCs) and has been
	immensely successful in selling them, chiefly to business.  It
	has often been said that "Nobody has ever been sacked for
	buying IBM".

	The {IBM PC} in its various versions has been so successful
	that unqualified reference to a "PC" almost certainly means a
	PC from IBM, or one of the many brands of {clone} produced by
	other manufacturers to cash in on IBM's original success.

	Alternative expansions of "IBM" such as Inferior But
	Marketable; It's Better Manually; Insidious Black Magic; It's
	Been Malfunctioning; Incontinent Bowel Movement, illustrate
	the considerable antipathy most hackers have long felt toward
	the "industry leader" (see {fear and loathing}).

	Quarterly sales $15351M, profits $689M (Aug 1994).

	{Home (http://www.ibm.com/)}.

	(1999-04-07)

1. The {supervisor} program or {operating system} on a
	computer.

	2. The entire computer system, including input/output devices,
	the {supervisor} program or {operating system} and possibly
	other {software}.

	3. Any large program.

	4. Any method or {algorithm}.

	[{Jargon File}]

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)