<hypertext> A program which allows a person to read
	{hypertext}.  The browser gives some means of viewing the
	contents of {nodes} (or "pages") and of {navigating} from one
	node to another.

	{Netscape Navigator}, {NCSA} {Mosaic}, {Lynx}, and {W3} are
	examples for browsers for the {World-Wide Web}.  They act as
	{clients} to remote {web servers}.

	(1996-05-31)

After-sale handholding; something many software vendors
	promise but few deliver.  To hackers, most support people are
	useless - because by the time a hacker calls support he or she
	will usually know the software and the relevant manuals better
	than the support people (sadly, this is *not* a joke or
	exaggeration).  A hacker's idea of "support" is a tte--tte
	or exchange of {electronic mail} with the software's designer.

	[{Jargon File}]

	(1995-02-15)

1. The portion of a {packet}, preceding the actual data,
	containing source and destination addresses, error checking
	and other fields.

	2. The part of an {electronic mail} message or {news} article
	that precedes the body of a message and contains, among other
	things, the sender's name and e-mail address and the date and
	time the message was sent.

<digital signal processing> The result of measuring the
	amplitude of an analog signal at a specified time.  In
	{digital signal processing} a sample is a signed or unsigned
	number and the number of samples per second is called the
	{sample rate}.

	(2001-06-06)

<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)

<networking> 1. A lasting connection between a user (or user
	agent) and a {peer}, typically a {server}, usually involving
	the exchange of many packets between the user's computer and
	the server.  A session is typically implemented as a layer in
	a network {protocol} (e.g. {telnet}, {FTP}).

	In the case of protocols where there is no concept of a
	session layer (e.g. {UDP}) or where sessions at the {session
	layer} are generally very short-lived (e.g. {HTTP}), {virtual}
	sessions are implemented by having each exchange between the
	user and the remote host include some form of {cookie} which
	stores state (e.g. a unique session ID, information about the
	user's preferences or authorisation level, etc.).

	See also {login}.

	2. A lasting connection using the {session layer} of a
	networking protocol.

	(1997-08-03)

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)

<data> A data structure holding many values, possibly of
	different types, which is usually accessed sequentially,
	working from the head to the end of the tail - an "ordered
	list".  This contrasts with a (one-dimensional) {array}, any
	element of which can be accessed equally quickly.

	Lists are often stored using a cell and pointer arrangement
	where each value is stored in a cell along with an associated
	pointer to the next cell.  A special pointer, e.g. zero, marks
	the end of the list.  This is known as a (singly) "linked
	list".  A doubly linked list has pointers from each cell to
	both next and previous cells.

	An unordered list is a {set}.

	(1998-11-12)

1. <file format> A single file containing one or (usually)
	more separate files plus information to allow them to be
	extracted (separated) by a suitable program.

	Archives are usually created for software distribution or
	{backup}.  {tar} is a common format for {Unix} archives, and
	{arc} or {PKZIP} for {MS-DOS} and {Microsoft Windows}.

	2. <operating system> To transfer files to slower, cheaper
	media (usually {magnetic tape}) to free the {hard disk} space
	they occupied.  This is now normally done for long-term
	storage but in the 1960s, when disk was much more expensive,
	files were often shuffled regularly between disk and tape.

	3. <networking> {archive site}.

	(1996-12-08)

A technique used to reduce network overhead, especially in
	{wide area networks} (WAN).

	Some network {protocols} send frequent packets for management
	purposes.  These can be {routing} updates or {keep-alive}
	messages.  In a {WAN} this can introduce significant overhead,
	due to the typically smaller {bandwidth} of WAN connections.

	Spoofing reduces the required bandwidth by having devices,
	such as {bridges} or {routers}, answer for the remote devices.
	This fools (spoofs) the {LAN} device into thinking the remote
	LAN is still connected, even though it's not.  The spoofing
	saves the WAN bandwidth, because no packet is ever sent out on
	the WAN.

	LAN {protocols} today do not yet accommodate spoofing easily.

	["Network Spoofing" by Jeffrey Fritz, BYTE, December 1994,
	pages 221 - 224].

	(1995-01-13)

<programming> A sequence of {data} values, usually {bytes},
	which usually stand for {characters} (a "character string").
	The {mapping} between values and characters is determined by
	the {character set} which is itself specified implcitly or
	explicitly by the environment in which the string is being
	interpreted.

	The most common character set is {ASCII} but, since the late
	1990s, there has been increased interest in larger character
	sets such as {Unicode} where each character is represented by
	more than eight {bits}.

	Most programming languages consider strings (e.g.
	"124:shabooya:\n", "hello world") basically distinct from
	numbers which are typically stored in fixed-length {binary} or
	{floating-point} representation.

	A {bit string} is a sequence of {bits}.

	(1999-12-21)

1. A program which provides some service to other ({client})
	programs.  The connection between client and server is
	normally by means of {message passing}, often over a
	{network}, and uses some {protocol} to encode the client's
	requests and the server's responses.  The server may run
	continuously (as a {daemon}), waiting for requests to arrive
	or it may be invoked by some higher level daemon which
	controls a number of specific servers ({inetd} on {Unix}).

	There are many servers associated with the {Internet}, such as
	those for {HTTP}, {Network File System}, {Network Information
	Service} (NIS), {Domain Name System} (DNS), {FTP}, {news},
	{finger}, {Network Time Protocol}.  On Unix, a long list can
	be found in /etc/services or in the {NIS} database "services".
	See {client-server}.

	2. A computer which provides some service for other computers
	connected to it via a network.  The most common example is a
	{file server} which has a local disk and services requests
	from remote clients to read and write files on that disk,
	often using {Sun}'s {Network File System} (NFS) {protocol} or
	{Novell Netware} on {PCs}.  Another common example is a {web
	server}.

	[{Jargon File}]

	(2003-12-29)

1. <programming> A property of a programming language where
	created objects and variables continue to exist and retain
	their values between runs of the program.

	2. <hardware> The length of time a phosphor dot on the screen
	of a {cathode ray tube} will remain illuminated after it has
	been energised by the electron beam.  Long-persistence
	phosphors reduce flicker, but generate ghost-like images that
	linger on screen for a fraction of a second.

	(1994-11-09)

1. <World-Wide Web> {HTTP cookie}.

	2. <protocol> A handle, transaction ID, or other token of
	agreement between cooperating programs.  "I give him a packet,
	he gives me back a cookie".

	The ticket you get from a dry-cleaning shop is a perfect
	mundane example of a cookie; the only thing it's useful for is
	to relate a later transaction to this one (so you get the same
	clothes back).

	Compare {magic cookie}; see also {fortune cookie}.

	3. <security, jargon> A {cracker} term for the {password} list
	on a {multi-user} computer.

	4. <jargon> An adjective describing a computer that just
	became {toast}.

	(1997-04-14)

<file format, filename extension> (jar) A compressed {archive}
	file containing {Java} {class} files, filename extension:
	".jar".  The {Java Development Kit} contains a tool called
	"jar" for creating .jar files, similar to the standard {Unix}
	{tar} command.  As well as archiving and compressing the Java
	class files, it also inserts a "manifest" file which can
	contain information about the class files, such as a {digital
	signature}.  Combining class files into a single archive file
	makes it possible to download them in a single {HTTP}
	transaction.  This, and the {compression}, speeds up execution
	of Java programs delivered via the {Internet}.

	(2001}-02-03)