Mainly because of memory restrictions, a serious flaw was designed into the 1984 PC, that may well cause chaos to computer systems on the fist day of the new millennium. Many other applications, such as older, and some new databases, may also have the same problem. Even if the system date is correct a number of software applications may misbehave as the year 2000 approaches.

Normally an application will get the date from the software based calendar of the operating system which is initialized, at boot up, from the BIOS firmware. The BIOS gets this date from the CMOS RTC hardware, which maintains a two-digit year from 00 to 99. These two digits are now prefixed, by the BIOS, with a stored pair of 'century digits', in this case 19, to compose the four digit year now presented to the operating system.

Since 1900 is an invalid year to the operating system the result is the date error of 04-01-1980. If the application was to take its date from the BIOS directly, instead of the operating system, it will receive the year 1900.

Although the fundermental transition design error was in the CMOS RTC, it is of no significance because no common appliction software uses it directly. All it does, after all is count the years from 00 to 99. A solution would be to increment the BIOS from 19 to 20.

Newer machine being produced contain BIOS code that monitor the CMOS RTC two digit year and by using a 'window' technique infer and supply the correct century(when seeing the year 1900),i.e. 2000 to the operating system).

There is software on the market that take your machine through the 1999 - 2000 transition year. A typical tester is 'Test2000' free from Year2000 Consultants Ltd. It does this by setting the BIOS date to 31-12-1999. 23:59:58 and observing the century change. A compliant BIOS will increment to 20.