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In computer science and computer programming, system time represents a computer system's notion of the passing of time. In this sense, ''time'' also includes the passing of days on the calendar. System time is measured by a ''system clock'', which is typically implemented as a simple count of the number of ''ticks'' that have transpired since some arbitrary starting date, called the ''epoch''. For example, Unix and POSIX-compliant systems encode system time ("Unix time") as the number of seconds elapsed since the start of the Unix epoch at 1 January 1970 00:00:00 UT, with exceptions for leap seconds. Systems that implement the 32-bit and 64-bit versions of the Windows API, such as Windows 9x and Windows NT, provide the system time as both SYSTEMTIME, represented as a year/month/day/hour/minute/second/milliseconds value, and FILETIME, represented as a count of the number of 100-nanosecond ticks since 1 January 1601 00:00:00 UT as reckoned in the proleptic Gregorian calendar. System time can be converted into calendar time, which is a form more suitable for human comprehension. For example, the Unix system time ' seconds since the beginning of the epoch translates into the calendar time ''9 September 2001 01:46:40 UT''. Library subroutines that handle such conversions may also deal with adjustments for timezones, daylight saving time (DST), leap seconds, and the user's locale settings. Library routines are also generally provided that convert calendar times into system times. == Other time measurements == 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. Process times are a tally of CPU instructions or clock cycles and generally have no direct correlation to wall time. File systems keep track of the times that files are created, modified, and/or accessed by storing timestamps in the file control block (or inode) of each file and directory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「System time」の詳細全文を読む スポンサード リンク
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