Year 2000-when is a clock not a clock?

摘要

The Year 2000 problem or the 'Millennium Bug' has been widely publicised in recent months. However, as the paper describes, the Year 2000 problem is a lot more than just making a clock function correctly as a timepiece. This is not a new phenomenon, and was known about in the 1970's, but it was only following the article entitled 'Doomsday 2000' (P. de Jager, 1993) that it received widespread recognition. The problem originated because of the high cost of data storage in the early computer systems. Using two extra bytes to store the full four digits of the year rather than just two was not considered justifiable. The Year 2000 problem can manifest itself in many ways and is also being used to refer to any date-related problem even if it does not occur in the Year 2000. One problem arose out of confusion about the status of Year 2000 as a leap year. Normally every four years is a leap year except for a Century year. However, every four hundred years the Century year is a leap year again and this was overlooked or not understood by many software teams. Many software systems do not handle the 29th February 2000 correctly, including some widely used applications. At midnight 31st December 1999, PC clocks can behave in a number of ways ranging from correctly handling the time and date to setting the year to '1900' or to some other figure such as '1980'. Systems that incorrectly increment the date at the start of the year may still be able to accept the year figure being manually set to '2000' and may thereafter function correctly. This is very dependent on the components used and the BIOS in use.