epoch
1. (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.<editor>
2. (Epoch) A version of GNU Emacs for the X Window System from NCSA.
[Jargon File]Last updated: 2004-06-10
Nearby terms:
EPIM ♦ epistasis ♦ EPL ♦ EPOC ♦ epoch ♦ EPP ♦ EPROM ♦ EPROM OTP ♦ EPROS ♦ EPS
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