epoch

n 1: a period marked by distinctive character or reckoned from a

fixed point or event [syn: {era}]

2: (astronomy) the precise date that is the point of reference

for which information (as coordinates of a celestial body)

is referred [syn: {date of reference}]

3: a unit of geological time

epoch

1. [Unix: probably from astronomical timekeeping] The time and

date corresponding to 0 in an operating system's clock and

timestamp values. Under most Unix versions the epoch is

00:00:00 GMT, January 1, 1970; under VMS, it's 00:00:00 of

November 17, 1858 (base date of the US Naval Observatory's

ephemerides); on a Macintosh, it's the midnight beginning

January 1 1904. System time is measured in seconds or {tick}s

past the epoch. Weird problems may ensue when the clock wraps

around (see {wrap around}), which is not necessarily a rare

event; on systems counting 10 ticks per second, a signed

32-bit count of ticks is good only for 6.8 years. The

1-tick-per-second clock of Unix is good only until January 18,

2038, assuming at least some software continues to consider it

signed and that word lengths don't increase by then. See also

{wall time}.

2. (Epoch) A version of {GNU Emacs} for the {X Window System}

from {NCSA}.

[{Jargon File}]