<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)

A collection of objects, known as the elements of the set,
	specified in such a way that we can tell in principle whether
	or not a given object belongs to it.  E.g. the set of all prime
	numbers, the set of zeros of the cosine function.

	For each set there is a {predicate} (or property) which is
	true for (possessed by) exactly those objects which are
	elements of the set.  The predicate may be defined by the set
	or vice versa.  Order and repetition of elements within the
	set are irrelevant so, for example, {1, 2, 3} = {3, 2, 1} =
	{1, 3, 1, 2, 2}.

	Some common set of numbers are given the following names:

	N = the {natural numbers} 0, 1, 2, ...

	Z = the {integers} ..., -2, -1, 0, 1, 2, ...

	Q = the {rational numbers} p/q where p, q are in Z and q /= 0.

	R = the {real numbers}

	C = the {complex numbers}.

	The empty set is the set with no elements.  The intersection
	of two sets X and Y is the set containing all the elements x
	such that x is in X and x is in Y.  The union of two sets is
	the set containing all the elements x such that x is in X or x
	is in Y.

	See also {set complement}.

	(1995-01-24)

<software> (Or "option", "flag", "switch", "option switch") An
	argument to a command that modifies its function rather than
	providing data.  Options generally start with "-" in {Unix} or
	"/" in {MS-DOS}.  This is usually followed by a single letter
	or occasionally a digit.

	Some commands require each option to be a separate argument,
	introduced by a new "-" or "/", others allow multiple option
	letters to be concatenated into a single argument with a
	single "-" or "/", e.g. "ls -al".  A few Unix commands
	(e.g. {ar}, {tar}) allow the "-" to be omitted.  Some options
	may or must be followed by a value, e.g. "cc prog.c -o prog",
	sometimes with and sometimes without an intervening space.

	{getopt} and {getopts} are commands for parsing command line
	options.  There is also a {C} library routine called getopt
	for the same purpose.

	(1996-12-11)

<file system> An element of data storage in a {file system}.

	The history of computing is rich in varied kinds of files and
	{file systems}, whether ornate (e.g., {Macintosh file system}
	for a well-known case) or deficient (e.g., many simple
	pre-1980s file systems don't allow {directories}).

	However, the prototypical file has these characteristics:

	* It is a single sequence of bytes (but consider {Macintosh}
	{resource forks}).

	* It has a finite length, unlike, e.g. a {Unix} {device}.

	* It is stored in a {non-volatile storage} medium (but see
	{ramdrive}).

	* It exists (nominally) in a {directory}.

	* It has a name that it can be referred to by in file
	operations, possibly in combination with its {path}.

	Additionally, a file system may associate other information
	with a file, such as {permission} bits or other {file
	attributes}; timestamps for file creation, last revision, and
	last access; revision numbers (a` la VMS), and other kinds of
	{magic}.

	Compare: {document}.

	(1997-04-08)

<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)

<operating system> See {Microsoft Windows}, {Windows NT}.

	(1997-11-23)

<operating system> A character string which tells a program to
	perform a specific action.  Most commands take {arguments}
	which either modify the action performed or supply it with
	input.  Commands may be typed by the user or read from a file
	by a {command interpreter}.  It is also common to refer to
	menu items as commands.

	(1997-06-21)

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)