The year 2038 problem (also known as Y2038, Y2K38, Y2K38 superbug or the Epochalypse) is a time formatting bug in computer systems that represent times after the time 03:14:07 UTC on 19 January 2038.
The problem exists in systems which measure Unix time – the number of seconds elapsed since the Unix epoch (00:00:00 UTC on 1 January 1970) – and store it in a signed 32-bit integer. The data type is only capable of representing integers between −(231) and 231 − 1, meaning the latest time that can be properly encoded is 231 − 1 seconds after epoch (03:14:07 UTC on 19 January 2038). Attempting to increment to the following second (03:14:08) will cause the integer to overflow, setting its value to −(231) which systems will interpret as 231 seconds before epoch (20:45:52 UTC on 13 December 1901). The problem is similar in nature to the year 2000 problem.
A lot of old PC hardware simply couldn’t scale to modern needs. On the plus side, things like virtualization and 64-bit architecture are helping solve issues like this.