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The Y1C Problem or Y1H Problem was a potential problem involving computers and computer systems in Taiwan.
Similar to the Y2K problem faced by much of the world in the lead-up to 2000, the Y1C (Y1H) problem is a side effect of Taiwan's use of the Minguo calendar for official purposes. This calendar is based on the founding of the Republic of China in 1912 (year 1), so the year 2011 on the Western Gregorian calendar corresponds to year 100 on Taiwan's official calendar, which posed potential problems for any program that only treats years as two-digit values.
As generally speaking only governmental offices used the official system, Y1C computer bug impact on the private sector was minimal. The potential to affect government systems was another matter. However, a large number of governmental computers were already using a three-digit system for dates, with a zero being used as the first digit for years below 100 (Gregorian 2010 or earlier).
Some government documents such as driver's licenses already refer to years over 100; nothing more than minor glitches were reported.
Some iPhone users reported that their alarm tool failed to function on 1 January 2011.
The North Korean (Juche) calendar was affected the same day as Taiwan's, as North Korea's calendar is also based on an event that happened in 1912 - the birthday of Kim Il-sung.