Year 10000 problem: Encyclopedia II - Year 10000 problem - Problems with date-handling programs

Year 10000 problem - Problems with date-handling programs

A lot of date-handling programs during the year 2000 displayed the year as 1900, 19100, or 100 because the programmers often simply inserted the text "19" in front of a calculation of the last two digits of the year as a shortcut or a way to save memory space. These sorts of date display errors are not likely to occur again when the year 10000 comes since this type of shortcut isn't useful in this case. However, some programs format dates in a way that only shows the last four digits. This is likely to cause the year 10000 to appear as "0000".

This problem can be seen today in the popular spreadsheet program Microsoft Excel, which stores dates as number of days since 31 December 1899 (day 1 is 1900-01-01), and the database program Microsoft Access, which stores dates as the number of days since 30 December 1899 (day 1 is 1899-12-31). In either application, entering a date value of 2,958,465 will yield the date 31 December 9999.

Incrementing this value by one causes what the applications call overflow, but in actuality the binary representation of 2,958,465 is 101101'00100100'10000001, while 2,958,466 is 101101'00100100'10000010. Both of these values use the same number of bits (22). The overflow that the applications refer to is most likely derived in their floating-point representations (day 1.5 is 1900-01-01T12:00:00 in Excel). They are likely stored as some variant of the IEEE floating-point standard number. The fractional portion of such numbers is 23 bits wide.

The Long Now Foundation is attempting to foster the custom of writing years with five digits, so that the year 2000 would be written as "02000", which would preempt the year 10,000 problem.

Adapted from the Wikipedia article "Problems with date-handling programs", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki