The time() system call first appeared in Version 1 AT&T UNIX. Through
the Version 3 AT&T UNIX, it returned 60 Hz ticks since an epoch that
changed occasionally, because it was a 32-bit value that overflowed in a
little over 2 years.
In Version 4 AT&T UNIX the granularity of the return value was reduced to
whole seconds, delaying the aforementioned overflow until 2038.
Version 7 AT&T UNIX introduced the ftime() system call, which returned
time at a millisecond level, though retained the gtime() system call
(exposed as time() in userland). time() could have been implemented as a
wrapper around ftime(), but that wasn't done.
4.1cBSD implemented a higher-precision time function gettimeofday() to
replace ftime() and reimplemented time() in terms of that.
Since FreeBSD 9 the implementation of time() uses
clock_gettime(CLOCK_SECOND) instead of gettimeofday() for performance
reasons.
With most valuable input from Warner (imp@).
Reviewed by: 0mp, jilles, imp
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D34751
3e0f3678ec