Epoch
1. <operating system> (Probably from astronomical timekeeping) A term used originally in
Unix documentation for the time and date corresponding to zero in an
operating system's
clock and timestamp values.
Under most Unix versions the epoch is 1970-01-01 00:00:00 GMT; under
VMS, it's 1858-11-17 00:00:00 (the base date of the US Naval Observatory's ephemerides); on a
Macintosh, it's 1904-01-01 00:00:00.
System time is measured in seconds or ticks 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 0.1 * 2**31-1 seconds, or 6.8 years. The one-tick-per-second clock of Unix is good only until 2038-01-18, assuming at least some software continues to consider it signed and that word lengths don't increase by then.
See also
wall time.
2. <editor> (Epoch) A version of
GNU Emacs for the
X Window System from
NCSA.
[
Jargon File]
