n. A future date when a disaster is expected or predicted, particularly a date that current computer software and hardware will interpret incorrectly, resulting in faulty logic or system failure.
In what could be called Y2K's little brother, one of the five computer 'doomsdates' falls Wednesday evening at midnight, when the calendar rolls over to Sept. 9, 1999 - or, numerically, 9/9/99.

All over the nation, people at power plants, telephone companies and some financial institutions will stay up late to make sure their computers don't mistake tomorrow's date for '9999,' a stop-program command that could, in theory, cause systems to crash.
—Bill Briggs, “Y2K-like glitch addressed to the nines,”
The Denver Post
, September 06, 1999
Jan. 1, 2000, is The Big One, kids. By now, you've heard that many of the world's computers will roll the date clock forward from '99' to '00' with potentially disastrous consequences…. But that isn't the only computer 'doomsdate' looming. A slew of lesser-known dates also could wreak technological havoc.
—Steve Woodward, “Jan. 1, 2000, isn't only 'doomsdate',” Star Tribune (Minneapolis, MN), October 17, 1998
1980 (earliest)
Although they're already bunkering down, most survivalists don't envision disaster by Labor — or even Election — Day. One popular doomsdate seems to be 1982, partly because that marks the expected arrival of the so-called "Jupiter effect," an unusual alignment of planets that some astronomers say will trigger assorted earthquakes, volcanoes and violent storms.
—Lynn Langway, “The Doomsday Boom,” Newsweek, August 11, 1980
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