Current Unix time () Unix time is a date and time representation widely used in computing. It measures time by the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the beginning of the Unix epoch, less adjustments made due to leap seconds. Unix time originated as the system time of Unix operating systems. It has come to be widely used in other computer operating systems, file systems, programming languages, and databases. Definition Two layers of encoding make up Unix time. The first layer encodes a point in time as a scalar real number which represents the number of seconds that have passed since 00:00:00UTC on Thursday, 1 January 1970. The second layer encodes that number as a sequence of bits or decimal digits. Unix time differs from both Coordinated Universal Time (UTC) and International Atomic Time (TAI) in its handling of leap seconds. UTC includes leap seconds that adjust for the discrepancy between precise time, as measured by atomic clocks, and solar time, relating to the position of the earth in relation to the sun. International Atomic Time (TAI), in which every day is precisely seconds long, ignores solar time and gradually loses synchronization with the Earth's rotation at a rate of roughly one second per year. In Unix time, every day contains exactly seconds but leap seconds are accounted for. Each leap second uses the timestamp of a second that immediately precedes or follows it. Encoding time as a number Unix time is a single signed number that increments every second, which makes it easier for computers to store and manipulate than conventional date systems. Interpreter programs can then convert it to a human-readable format. The Unix epoch is the time 00:00:00UTC on 1 January 1970. There is a problem with this definition, in that UTC did not exist in its current form until 1972; this issue is discussed below. For brevity, the remainder of this section uses ISO 8601 date and time format, in which the Unix epoch is 1970-01-01T00:00:00Z. The Unix time number is zero at the Unix epoch and increases by exactly per day since the epoch. Thus 2004-09-16T00:00:00Z, days after the epoch, is represented by the Unix time number × = . This can be extended backwards from the epoch too, using negative numbers; thus 1957-10-04T00:00:00Z, days before the epoch, is represented by the Unix time number × = .