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The year 1900 problem is a problem concerning the understanding of during which century an event occurred; in this case, before or after the year 1900. Unlike the year 2000 problem, it is not a problem tied to computer software alone, since the problem existed before electronic computers did. Such problems have also cropped up in manual systems.
The most common issue raised by the year 1900 problem regards how people's birthdays were registered. Often, the birth year has been registered with only two digits, assuming either when designing the routine that it was not important exactly how old people were, or (perhaps erroneously) that everyone was less than one hundred years old. In the late 20th century (before the year 2000), everyone alive at the time was born in either the 19th or 20th century.
In several countries, especially in Europe, a national identification number was introduced (often in the 1950s), including two-digit information about the birth year. The largest unwelcome side-effect from this was that people 100 or more years old were mistaken for small children.
When handling the year 2000 problem, measures were sometimes taken to avoid or rectify this: modifying the national identification number, for instance, although the same issue existed with the year 1900 problem.
Microsoft Excel
Microsoft Excel has its own year 1900 problem: it cannot display dates before year 1900. This is not a problem associated with two-digit year representation or similar; Microsoft Excel uses a floating point number to store dates and times. The number one represents January 1st 1900. Numbers below zero will be displayed as an error. Put simply, the ability to display dates before 1900 is not included.
