This page covers the following topics -
The BIOS (Basic Input Output System) is a hardware interface program between the basic computer hardware and the operating system that provides a standardized interface between the operating system and the hardware.
One of these standard interfaces is between the Real Time Clock in the hardware and the operating system. In general, most of the Real Time Clock hardware made before 1995 did not allow for a year greater than 1999; thus the "Y2K Problem."
A second level of confusion in this area is the fact that most operating systems request the date from the Real Time Clock only upon startup; they maintain an independent copy in parallel to the hardware while the system is running. And then the next system restart goes back to read the hardware value. As such, tests that set the operating system time to a few minutes before the end of the century and then get a readout a few minutes later do not test the entire hardware. It is necessary to set the operating system date and time to 23:57 on December 31, 1999 and then turn the power off for a few minutes. If the system time is not correct, it is probably desirable to upgrade the BIOS.
Major BIOS manufacturers are -