- noun the inability to handle dates later than 1999. This problem, which came to light in the 1990s, affected old hardware and software that stored dates as two digits, with the ‘19’ being assumed. Such dates would not move to ‘2000’ at the turn of the millennium but would revert to ‘1900’, with unpredictable and possibly serious results for the affected systems. In the event, the affected systems were nearly all modified in time. There were very few problems when the year 2000 arrived, and the more apocalyptic predictions did not come to pass.