Year 10,000 problem

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The year 10,000 problem is the collective name for all potential software bugs that may emerge as the need to express years with five digits arises. In the months leading up to the beginning of the year 2000 (see the Year 2000 problem), the year 10,000 problem was given somewhat humorous exposure by people in the media.

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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, but this in turn would be susceptible to the Year 100,000 problem.

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Problems with records

The year 2000 problem came about because two digits were used for four-digit years and the century could not be reliably determined. The years recorded had to have two century digits added to solve the problem. The year 10,000 problem will not require updating any old records because four digits is sufficient for four-digit years. It will only require new records to use five digits. There is, however, a potential problem with record sets that make use of lexical sorting. For example, possible representations dates in the year 10000 could appear adjacent to dates in the year 1000 rather than the year 9999 as intended.

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