Wednesday, November 12, 2014

Computer Time Jargon: Unix Epoch, UTC, GMT

Computers represent TIME with many words that have similar meaning.  It creates a wall of words to climb before understanding.



UNIX Time = UNIX Epoch Time = Epoch Time = POSIX Time 

  • the number of seconds since 1/1/1970, the year Unix was born 
    • Unix computers count the time in seconds since its official "birthday," -- called "epoch" in computing terms -- which is Jan. 1, 1970.  
    • Unix engineers needed to set a uniform date for the start of computing time, and New Year's Day, 1970, the same year they started developing it, seemed most convenient.
    • Linux follows the same tradition. [Reference]
    • Years < 1970 are negative
  • Timezone it represents ALWAYS equals UTC = Universal Time = GMT [Reference]
  • More Jargon:
    • Epoch = reference point from which time is measured
    • POSIX = Portable Operating System Interface.  These are the standards that Unix and Linux were built upon.
UTC = Coordinated Universal Time = GMT = Greenwich Mean Time

  • Timezones around the world are expressed as positive or negative offsets from UTC.



REFERENCES
http://unix.stackexchange.com/questions/26205/why-does-unix-time-start-at-1970-01-01

#Wall.Of.Words #computing

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