Special Years

I notice 1900 1970 and 1601 are used in time presentation.
1900: ts.tm_year is number of year since 1900.
ts is a struct, returned by localtime and gmtime, and get converted to string by asctime
1970: time_t is the number of seconds since start of this year UTC. returned by time and mktime(tm)
This is called Epoch AKA Unix timestamps and POSIX time. converted to string by ctime.
1601: FILETIME on Windows, 64bit, is the number of 0.1ms since start of this year in UTC
This year is the start of a 400-year cycle in Gregorian calendar.