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Software timekeeping systems vary widely in the resolution of time measurement; some systems may use time units as large as a day, while others may use nanoseconds.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 ...
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 −(2 31 ) and 2 31 − 1 , meaning the latest time that can be properly encoded is 2 31 − 1 ...
When dealing with periods that do not encompass a UTC leap second, the difference between two Unix time numbers is equal to the duration in seconds of the period between the corresponding points in time. This is a common computational technique. However, where leap seconds occur, such calculations give the wrong answer.
System.DateTime.Now [19] System.DateTime.UtcNow [20] 100 ns [21] 1 January 0001 to 31 December 9999 CICS: ASKTIME: 1 ms 1 January 1900 COBOL: FUNCTION CURRENT-DATE: 1 s 1 January 1601 Common Lisp (get-universal-time) 1 s 1 January 1900 Delphi date time: 1 ms (floating point) 1 January 1900 Delphi (Embarcadero Technologies) [22] System.SysUtils ...
For example, Unix time is represented as the number of seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds. An epoch in astronomy is a reference time used for consistency in calculation of positions and orbits. A common astronomical epoch is J2000, which is noon on January 1, 2000, Terrestrial Time.
[17] The separator used between date values (year, month, week, and day) is the hyphen, while the colon is used as the separator between time values (hours, minutes, and seconds). For example, the 6th day of the 1st month of the year 2009 may be written as "2009-01-06" in the extended format or as "20090106" in the basic format without ambiguity.
The latest time that can be represented in this form is 03:14:07 UTC on Tuesday, 19 January 2038 (corresponding to 2,147,483,647 seconds since the start of the epoch). This means that systems using a 32-bit time_t type are susceptible to the Year 2038 problem. [9]
Some file archivers and some version control software, when they copy a file from some remote computer to the local computer, adjust the timestamps of the local file to show the date/time in the past when that file was created or modified on that remote computer, rather than the date/time when that file was copied to the local computer.