Of the only two satellite systems with global coverage, GPS calculates its time signal from an epoch, whereas GLONASS calculates time as an offset from UTC, with the UTC input adjusted for leap seconds. There are at least six satellite navigation systems, all of which function by transmitting time signals.
#Computer time converter software
On systems where date and time are important in the human sense, software will nearly always convert this internal number into a date and time representing a human calendar. Such representation of time is mainly for internal use.
When times prior to the epoch need to be represented, it is common to use the same system, but with negative numbers. For example, for an epoch date of midnight UTC (00:00) on 1 January 1900, and a time unit of a second, the time of the midnight (24:00) between 1 January 1900 and 2 January 1900 is represented by the number 86400, the number of seconds in one day. Software timekeeping systems vary widely in the precision of time measurement (granularity) some systems may use time units as large as a day, while others may use nanoseconds. The NT time epoch on Windows NT and later refers to the Windows NT system time in (10^-7)s intervals from 0h 1 January 1601.Ĭomputing epochs are nearly always specified as midnight Universal Time on some particular date. For instance, Unix and POSIX measure time as the number of seconds that have passed since 1 January 1970 00:00:00 UT, a point in time known as the Unix epoch. Most computer systems determine time as a number representing the seconds removed from particular arbitrary date and time. In computing, an epoch is a date and time from which a computer measures system time.
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