POSIX time, or UNIX time, is a system that describes points in time. UNIX measures time by the number of seconds since the midnight proleptic UTC (Coordinated Universal Time) of January 1, 1970. This method of time measuring is widely used in UNIX operating systems as well as many other file formats and computer systems. It is neither a true representation nor linear representation of UTC, although it is often mistaken for both. This is because true UTC counts leap seconds, but UNIX time does not. On some computers, you can check your UNIX time by typing ‘date +%s’ in the command line console.

UNIX timing is made up of two encoded layers and both of these layers can be separated to make them more useful. The first layer encodes time as a real number, and the second layer encodes the number in a string of bits or another form of code.

All modern UNIX time is strictly based on UTC, which allows time to be counted by using SI seconds. An average UTC day is about 86,400 seconds long, but because of leap seconds they can occasionally be measured to 86,399 or 86,401. When there is a leap second, the UTC day is not exactly 86,400 seconds long so a discontinuity occurs with the UNIX time frame because UNIX timing has 86,400 seconds every day, regardless of leap second. When leap seconds are deleted, the UNIX number will jump up by one.

Although UNIX time is convenient for computer systems, it can be difficult to read for most people. A Unix time converter can help to convert the UNIX strings into a time frame that is more intelligible. There are many time converters available online and most of them only require you to input the UNIX time string so the program can automatically convert it.