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The command is also available in the Motorola VERSAdos, [5] Intel iRMX 86, [6] PC-MOS, [7] SpartaDOS X, [8] ReactOS, [9] SymbOS, and DexOS operating systems as well as in the EFI shell. [10] On MS-DOS, the command is available in versions 1 and later. [11] In Unix, the date command displays and sets both the time and date, in a similar manner.
computes the difference in seconds between two time_t values time: returns the current time of the system as a time_t value, number of seconds, (which is usually time since an epoch, typically the Unix epoch). The value of the epoch is operating system dependent; 1900 and 1970 are often used. See RFC 868. clock
Closely related to system time is process time, which is a count of the total CPU time consumed by an executing process.It may be split into user and system CPU time, representing the time spent executing user code and system kernel code, respectively.
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 ...
On 5 January 1975, the 12-bit field that had been used for dates in the TOPS-10 operating system for DEC PDP-10 computers overflowed, in a bug known as "DATE75". The field value was calculated by taking the number of years since 1964, multiplying by 12, adding the number of months since January, multiplying by 31, and adding the number of days since the start of the month; putting 2 12 − 1 ...
[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.
It encodes times with values that differ by several seconds from the POSIX time values. A version of this system, in which the epoch was 1970-01-01T00:00:00 TAI rather than 1970-01-01T00:00:10 TAI, was proposed for inclusion in ISO C's time.h, but only the UTC part was accepted in 2011. [9] A tai_clock does, however, exist in C++20.
Fractional days are often calculated in UTC or TT, although Julian Dates use pre-1925 astronomical date/time (each date began at noon = ".0") and Microsoft Excel uses the local time zone of the computer. Using fractional days reduces the number of units in time calculations from four (days, hours, minutes, seconds) to just one (days).