At boot-up, the BIOS reads the information from the Real Time Clock that is stored in CMOS and interprets it. Year 2000 compliant will understand that the century must roll from 19 to 20. If the BIOS cannot be upgraded, or if you do not wish to flash the BIOS, it may be possible to correct the problem through the operating system on the machine. About RTC, BIOS, and the beginning of DOS time. Be aware that the server also needs to be Year 2000 compliant, but that making the server compliant will not necessarily solve the problem for non-compliant PCs on the network.
Applications often keep track of dates for calculations, sorting, record deletion, etc.
Typically, they get the date from the operating system, but they may contain date logic of their own that may be affected. Date logic may affect how the date is actually stored, or how it is displayed. Date arithmetic is especially vulnerable to date problems. For example, if the user only enters two digits of a year, the program very likely makes an assumption about what the first two digits of the year should be.