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Definition: epoch

The starting date from which time is measured as a number of days or minutes or seconds, etc. In computer applications, epochs are used to maintain a time reference as a single number for ease of computation. Otherwise, depending on the granularity of time desired, every point in time would have to be stored with some of or all of the components of the time hierarchy, including year, month, day, hour, minute, second, millisecond, microsecond and nanosecond. Following are the various epochs in use. See also EPOC.

  System          Epoch            Measured in

  Unix/Linux      Jan. 1, 1970     Seconds
  Java            Jan. 1, 1970     Milliseconds

  Windows files   Jan. 1, 1601     Ticks (100 ns)
  Windows dates   Jan. 1, 0001     Ticks (100 ns)

  Mac             Jan. 1, 2001     Seconds
  Earlier Mac     Jan. 1, 1904     Seconds

  Excel           Dec. 31, 1899    Days
  DB2             Dec. 31, 1899    Days

  Unununium       Jan. 1, 2000     Microseconds

No USB Drives in 1969
When this USB drive was formatted, the date was reset to the epoch. The 7:00pm tells us it was done on the East Coast, five hours behind the UTC time of January 1, 1970 (see above). This info comes from the Mac that the drive was plugged into.