3 ms·
For RTC storage in CMOS using a BCD byte, one could assume that the epoch was relative to, say the decade of manufacturing (suppose 1990) such that dates roll o
by burnt-resistor 1y ago
For RTC storage in CMOS using a BCD byte, one could assume that the epoch was relative to, say the decade of manufacturing (suppose 1990) such that dates roll over from 99 to 00 could instead create a Y2090 problem:
Y = (yy < 90) ? (2000 + yy) : (1900 + yy);
This would have to be handled differently than something that was required to be IBM PC or IBM AT compatible with every compatible quirk. It's simply a way to save 8-bits of battery-backed SRAM or similar.