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. 2. (Epoch) A version of GNU Emacs for the {X Window System} from {NCSA}. [Jargon File] (2004-06-10)
