What is Unix Time?

Unix time (also known as Epoch time, POSIX time, seconds since the Epoch, or UNIX Epoch time) is a system for describing a point in time.

The Definition

It is the number of seconds that have elapsed since the Unix epoch, minus leap seconds. The Unix epoch is 00:00:00 UTC on 1 January 1970.

Why is it used?

Timezones are incredibly complex. Daylight saving time changes, geopolitical boundary adjustments, and local laws make calculating the duration between two points in time extremely difficult if you represent time asYYYY-MM-DD HH:MM:SS.

Unix time simplifies this by representing a point in time as a single integer. Because it is simply a running total of seconds, calculating the time elapsed between two timestamps is as simple as subtracting one integer from another.

The Year 2038 Problem

Because many older systems store Unix time as a signed 32-bit integer, the maximum value it can hold is2,147,483,647. This timestamp corresponds to January 19, 2038, at 03:14:07 UTC.

After this point, 32-bit systems will "roll over" and interpret the time as a negative number, effectively jumping back to December 1901. Modern systems avoid this by using 64-bit integers to store the timestamp, which will be sufficient for the next 292 billion years.