Guy Harris <guy@alum.mit.edu> writes:
I don't know what the lowest layers of Windows (NT) use (I don't have any "NT Native API" documentation handy), but the Windows API offers GetSystemTimeAsFileTime(), which supplies tenths-of-microseconds-since-the-FILETIME-epoch ("January 1, 1601 (UTC)", using the proleptic Gregorian calendar and some probably-proleptic form of UTC), so it can do UTC as well. ... Caché runs atop Windows, assorted UN*Xes, and OpenVMS. SYS$GETTIME on VMS supplies "the number of 100-nanosecond intervals since November 17, 1858."
In the department of weird epoch reference dates: I have a very distinct recollection that HYDRA/C.mmp[1] ran their system clock in microseconds since Charles Babbage's birthday (26 December 1791). Unfortunately I can't find any evidence other than 40-plus-year-old memory to support that. The C.mmp book cited by Wikipedia describes the clock as being 56 bits wide, which would be plenty for that timespan, but there's nothing in it about the timekeeping convention. regards, tom lane [1] https://en.wikipedia.org/wiki/C.mmp