Millennium Bug

Crisis that faced computer professionals and users at the end of the year 1999. The crisis arose because it was feared that computers would be unable to operate normally when faced with the unfamiliar date format of the year 2000. Information about the year was typically stored in a two-digit instead of a four-digit field in order to save memory space, which without remedial work would have meant that after the year 1999 ended the year could have appeared as ‘00’, interpreted as 1900 or not recognized at all. The turn of the century itself passed without significant breakdowns of normal services.

Many computer systems rely on the storage and use of dates to function, and many of the systems in use today were developed without taking into account the implications of the century date change. All affected parties in government, public sectors, and industry, had to prepare for the end of the century by testing and upgrading equipment and systems as necessary. Action to minimize these problems started in the mid 1990s.

Failures that occurred at the end of 1999 included safety systems in nuclear power stations, electrocardiograph machines, and the USA's defence intelligence satellites, but these problems passed largely unnoticed amidst the worldwide celebrations of the turn of the millennium, and the predicted shortages and breakdown of law and order did not materialize.