Epoch

In computing, an epoch is a measurable range of time that is supported by an operating system or drive format.

Start dates

 * The epoch of classic Mac OS and HFS begins at midnight on January 1, 1904.
 * The Unix epoch, used by most Unix-based systems like Mac OS X and its derivatives, such as iOS, iPadOS, macOS, and watchOS, begins at midnight on January 1, 1970.

End dates

 * The epoch of early 32-bit Unix-based systems (such as Mac OS X prior to 10.6, or iPhone 5 and earlier) ends on January 19, 2038 at 03:14:07.
 * The epoch of HFS and HFS+ ends on February 6, 2040 at 06:28:15.
 * The epoch of APFS ends on July 21, 2554 at 23:34:33.