1. <language> {Synthesizer Specification Language}.

	2. <language> {Syntax/Semantic Language} (S/SL).

	3. <networking, World-Wide Web> {Secure Sockets Layer}.

	(1996-09-08)

<operating system, programming> The process of carrying out
	the {instructions} in a computer program by a computer.

	See also {dry run}.

	(1996-05-13)

<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)

<programming> (See below for synonyms) A data structure for
	storing items which are to be accessed in last-in first-out
	order.

	The operations on a stack are to create a new stack, to "push"
	a new item onto the top of a stack and to "pop" the top item
	off.  Error conditions are raised by attempts to pop an empty
	stack or to push an item onto a stack which has no room for
	further items (because of its implementation).

	Most processors include support for stacks in their
	{instruction set architectures}.  Perhaps the most common use
	of stacks is to store {subroutine} arguments and return
	addresses.  This is usually supported at the {machine code}
	level either directly by "jump to subroutine" and "return from
	subroutine" instructions or by {auto-increment} and
	auto-decrement {addressing modes}, or both.  These allow a
	contiguous area of memory to be set aside for use as a stack
	and use either a special-purpose {register} or a general
	purpose register, chosen by the user, as a {stack pointer}.

	The use of a stack allows subroutines to be {recursive} since
	each call can have its own calling context, represented by a
	stack frame or {activation record}.  There are many other
	uses.  The programming language {Forth} uses a data stack in
	place of variables when possible.

	Although a stack may be considered an {object} by users,
	implementations of the object and its access details differ.
	For example, a stack may be either ascending (top of stack is
	at highest address) or descending.  It may also be "full" (the
	stack pointer points at the top of stack) or "empty" (the
	stack pointer points just past the top of stack, where the
	next element would be pushed).  The full/empty terminology is
	used in the {Acorn Risc Machine} and possibly elsewhere.

	In a list-based or {functional language}, a stack might be
	implemented as a {linked list} where a new stack is an empty
	list, push adds a new element to the head of the list and pop
	splits the list into its head (the popped element) and tail
	(the stack in its modified form).

	At {MIT}, {pdl} used to be a more common synonym for stack,
	and this may still be true.  {Knuth} ("The Art of Computer
	Programming", second edition, vol. 1, p. 236) says:

	  Many people who realised the importance of stacks and queues
	  independently have given other names to these structures:
	  stacks have been called push-down lists, reversion storages,
	  cellars, dumps, nesting stores, piles, last-in first-out
	  ("LIFO") lists, and even yo-yo lists!

	[{Jargon File}]

	(1995-04-10)

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}]

<messaging> (e-mail) Messages automatically passed from one
	computer user to another, often through computer {networks}
	and/or via {modems} over telephone lines.

	A message, especially one following the common {RFC 822}
	{standard}, begins with several lines of {headers}, followed
	by a blank line, and the body of the message.  Most e-mail
	systems now support the {MIME} {standard} which allows the
	message body to contain "{attachments}" of different kinds
	rather than just one block of plain {ASCII} text.  It is
	conventional for the body to end with a {signature}.

	Headers give the name and {electronic mail address} of the
	sender and recipient(s), the time and date when it was sent
	and a subject.  There are many other headers which may get
	added by different {message handling systems} during delivery.

	The message is "composed" by the sender, usually using a
	special program - a "{Mail User Agent}" (MUA).  It is then
	passed to some kind of "{Message Transfer Agent}" (MTA) - a
	program which is responsible for either delivering the message
	locally or passing it to another MTA, often on another {host}.
	MTAs on different hosts on a network often communicate using
	{SMTP}.  The message is eventually delivered to the
	recipient's {mailbox} - normally a file on his computer - from
	where he can read it using a mail reading program (which may
	or may not be the same {MUA} as used by the sender).

	Contrast {snail-mail}, {paper-net}, {voice-net}.

	The form "email" is also common, but is less suggestive of the
	correct pronunciation and derivation than "e-mail".  The word
	is used as a noun for the concept ("Isn't e-mail great?", "Are
	you on e-mail?"), a collection of (unread) messages ("I spent
	all night reading my e-mail"), and as a verb meaning "to send
	(something in) an e-mail message" ("I'll e-mail you (my
	report)").  The use of "an e-mail" as a count noun for an
	e-mail message, and plural "e-mails", is now (2000) also well
	established despite the fact that "mail" is definitely a mass
	noun.

	Oddly enough, the word "emailed" is actually listed in the
	Oxford English Dictionary.  It means "embossed (with a raised
	pattern) or arranged in a net work".  A use from 1480 is
	given.  The word is derived from French "emmailleure",
	network.  Also, "email" is German for enamel.

	{The story of the first e-mail message
	(http://www.pretext.com/mar98/features/story2.htm)}.

	(2002-07-14)

1. <operating system> (Or "erase") To make a file
	inaccessible.

	Usually this operation only deletes information from the
	tables the {file system} uses to locate named files; the
	file's contents still exist on {disk} and can sometimes be
	recovered by scanning the whole disk for strings which are
	known to have been in the file.  Files created subsequently on
	the same disk are quite likely to reuse the same blocks and
	thus overwrite the deleted file's data permanently.

	2. <character> The {control character} with {ASCII} code 127.
	Usually entering this character from the keyboard deletes the
	last character typed from the {input buffer}.  Sadly there is
	great confusion between {operating systems} and keyboard
	manufacturers as to whether this function should be assigned
	to the delete or {backspace} key/character.

	The choice of code 127 (binary 1111111) is not arbitrary but
	dates back to the use of {paper tape} for input.  The delete
	key rewound the tape by one character and punched out all
	seven holes, thus obliterating whatever character was there
	before.  The tape reading software ignored any delete
	characters in the input.

	(1996-12-01)

<networking, protocol> (TLS) A {protocol} designed to allow
	{client/server} applications to communicate over the
	{Internet} without {eavesdropping}, {tampering}, or {message
	forgery}.

	TLS is defined in {RFC 2246}.

	(2003-10-03)

<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)

<programming> An unwanted and unintended property of a program
	or piece of hardware, especially one that causes it to
	malfunction.  Antonym of {feature}.  E.g. "There's a bug in
	the editor: it writes things out backward."  The
	identification and removal of bugs in a program is called
	"{debugging}".

	Admiral {Grace Hopper} (an early computing pioneer better
	known for inventing {COBOL}) liked to tell a story in which a
	technician solved a {glitch} in the {Harvard Mark II machine}
	by pulling an actual insect out from between the contacts of
	one of its relays, and she subsequently promulgated {bug} in
	its hackish sense as a joke about the incident (though, as she
	was careful to admit, she was not there when it happened).
	For many years the logbook associated with the incident and
	the actual bug in question (a moth) sat in a display case at
	the Naval Surface Warfare Center (NSWC).  The entire story,
	with a picture of the logbook and the moth taped into it, is
	recorded in the "Annals of the History of Computing", Vol. 3,
	No. 3 (July 1981), pp. 285--286.

	The text of the log entry (from September 9, 1947), reads
	"1545 Relay #70 Panel F (moth) in relay.  First actual case of
	bug being found".  This wording establishes that the term was
	already in use at the time in its current specific sense - and
	Hopper herself reports that the term "bug" was regularly
	applied to problems in radar electronics during WWII.

	Indeed, the use of "bug" to mean an industrial defect was
	already established in Thomas Edison's time, and a more
	specific and rather modern use can be found in an electrical
	handbook from 1896 ("Hawkin's New Catechism of Electricity",
	Theo. Audel & Co.)  which says: "The term "bug" is used to a
	limited extent to designate any fault or trouble in the
	connections or working of electric apparatus."  It further
	notes that the term is "said to have originated in
	{quadruplex} telegraphy and have been transferred to all
	electric apparatus."

	The latter observation may explain a common folk etymology of
	the term; that it came from telephone company usage, in which
	"bugs in a telephone cable" were blamed for noisy lines.
	Though this derivation seems to be mistaken, it may well be a
	distorted memory of a joke first current among *telegraph*
	operators more than a century ago!

	Actually, use of "bug" in the general sense of a disruptive
	event goes back to Shakespeare!  In the first edition of
	Samuel Johnson's dictionary one meaning of "bug" is "A
	frightful object; a walking spectre"; this is traced to
	"bugbear", a Welsh term for a variety of mythological monster
	which (to complete the circle) has recently been reintroduced
	into the popular lexicon through fantasy {role-playing games}.

	In any case, in jargon the word almost never refers to
	insects.  Here is a plausible conversation that never actually
	happened:

	"There is a bug in this ant farm!"

	"What do you mean?  I don't see any ants in it."

	"That's the bug."

	[There has been a widespread myth that the original bug was
	moved to the Smithsonian, and an earlier version of this entry
	so asserted.  A correspondent who thought to check discovered
	that the bug was not there.  While investigating this in late
	1990, your editor discovered that the NSWC still had the bug,
	but had unsuccessfully tried to get the Smithsonian to accept
	it - and that the present curator of their History of
	American Technology Museum didn't know this and agreed that it
	would make a worthwhile exhibit.  It was moved to the
	Smithsonian in mid-1991, but due to space and money
	constraints has not yet been exhibited.  Thus, the process of
	investigating the original-computer-bug bug fixed it in an
	entirely unexpected way, by making the myth true!  - ESR]

	[{Jargon File}]

	(1999-06-29)

1. <hardware> An electrical conductor.  For distances larger
	than a breadbox, a single line may consist of two electrical
	conductors in twisted, parallel, or concentric arrangement
	used to transport one logical signal.

	By extension, a (usually physical) medium such as an {optical
	fibre} which carries a signal.

	(1995-09-29)