epoch

1. 1. A particular period of history, especially one considered remarkable or noteworthy.
   2. A notable event that marks the beginning of such a period. See synonyms at period.
2. A unit of geologic time that is a division of a period.
3. Astronomy. An instant in time that is arbitrarily selected as a point of reference.

[Medieval Latin epocha, measure of time, from Greek epokhē, a point in time.]

For more information on epoch, visit Britannica.com.

The starting date from which time is measured as a number of days or minutes or seconds, etc. In computer applications, epochs are used to maintain a time reference as a single number for ease of computation. Otherwise, depending on the granularity of time desired, every point in time would have to be stored with some of or all of the components of the time hierarchy, including year, month, day, hour, minute, second, millisecond, microsecond and nanosecond. Following are the various epochs in use. See also EPOC.

  System          Epoch            Measured in

  Unix            Jan. 1, 1970     Seconds
  Java            Jan. 1, 1970     Milliseconds

  Windows files   Jan. 1, 1601     Ticks (100 ns)
  Windows dates   Jan. 1, 0001     Ticks (100 ns)

  Mac             Jan. 1, 2001     Seconds
  Earlier Mac     Jan. 1, 1904     Seconds

  Excel           Dec. 31, 1899    Days
  DB2             Dec. 31, 1899    Days

  Unununium       Jan. 1, 2000     Microseconds

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noun

A particular time notable for its distinctive characteristics: age, day, era, period, time (often used in plural). See time.

[Unix: prob.: from astronomical timekeeping] The time and date corresponding to 0 in an operating system's clock and timestamp values. Under most Unix versions the epoch is 00:00:00 GMT, January 1, 1970; under VMS, it's 00:00:00 of November 17, 1858 (base date of the U.S. Naval Observatory's ephemerides); on a Macintosh, it's the midnight beginning January 1 1904. System time is measured in seconds or ticks past the epoch. Weird problems may ensue when the clock wraps around (see wrap around), which is not necessarily a rare event; on systems counting 10 ticks per second, a signed 32-bit count of ticks is good only for 6.8 years. The 1-tick-per-second clock of Unix is good only until January 18, 2038, assuming at least some software continues to consider it signed and that word lengths don't increase by then. See also wall time. Microsoft Windows, on the other hand, has an epoch problem every 49.7 days — but this is seldom noticed as Windows is almost incapable of staying up continuously for that long.

[Etymology: Gk: ‘pause’] time A specific point in time or the interval between two such points, but not as such a measure of time. In astronomy it is usually the single point, otherwise it generally has the extended meaning; in geology it can be millions of years. By contrast, an epoch within the initial cosmic ‘big bang’ is less than a microsecond.

geology The fourth-largest unit (following period) of the geochronologic scale, and the tertiary one into which it, excluding the pre-Cambrian, is divided: examples include Pliocene, Pleistocene, and Holocene. Typical size is about 15 million years.

Tutor's tip: The "epic" (a long poem or other writing telling of a nation's heroic acts) adventure tale takes place during the "epoch" (a period of time in history or in geology) after the Bronze Age.

Look up epoch in Wiktionary, the free dictionary.

An epoch, Epoch or EPOCH may refer to:

An epoch (periodization)

• Epoch (reference date), a moment in time chosen as the origin of a particular era
• Epoch (geology) or geologic epoch, a span of time smaller than a "period" and larger than an "age", on the geologic time scale
• Epoch (cosmology) or cosmologic epoch, a phase in the development of the universe since the Big Bang
• Epoch (astronomy), a moment in time used as a reference for the orbital elements of a celestial body
• Epoch (race), racial periods after Blavatsky's Root Races theories
• A step in the training process of an artificial neural network

EPOCH or Epoch (proper noun)

• Epoch (magazine), literary magazine of Cornell University
• Epoch (film), a 2001 science fiction TV film directed by Matt Codd
• Epoch Game Pocket Computer, an early hand-held game console
• Epoch Co., the maker of the above and other computer games
• Epoch (Chrono Trigger), a flying time machine in role-playing game Chrono Trigger
• Epoch (DC Comics), a supervillain also known as the Lord of Time
• Epoch (Marvel Comics), a cosmic entity in the Marvel Comics universe
• Epoch Javascript Calendar, a calendar component for use in web pages
• EPOCh, part of the EPOXI space mission
• EPOCH, European Parallel Operating System based on ChorusOS
• Epoch, an eco-friendly racing car concept vehicle by Kumho Tires
• EPOCH, a chemotherapy regimen for some non-Hodgkin lymphomas comprising Etoposide, Prednisone, Oncovin, Cyclophosphamide, Hydroxydaunorubicin
• The Epoch Times, a privately owned Falun Gong-linked newspaper
• Epoch Hunter, a boss in Caverns of Time from the game World of Warcraft
• Cross Epoch, a crossover chapter of the Dragon Ball and One Piece manga
• Ha-Tsefirah (lit. Epoch), a Hebrew language newspaper published in 1862 and 1874-1931
• EPOCH (album), a 2006 album released by the Japanese hip hop group Rip Slyme

See also

Epic

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Dansk (Danish)
n. - epoke, periode, tid

Nederlands (Dutch)
tijdvak, periode, belangrijke datum of gebeurtenis, mijlpaal

Français (French)
n. - époque, période, (fig) date

Deutsch (German)
n. - Epoche

Ελληνική (Greek)
n. - εποχή, χρονική περίοδος

Italiano (Italian)
epoca

Português (Portuguese)
n. - época (f), período (m)

Русский (Russian)
эпоха, эра, век

Español (Spanish)
n. - época, era, período

Svenska (Swedish)
n. - epok

中文（简体）(Chinese (Simplified))
新纪元, 时期, 时代

中文（繁體）(Chinese (Traditional))
n. - 新紀元, 時期, 時代

한국어 (Korean)
n. - 신기원, 지층 구성 기간

日本語 (Japanese)
n. - 新紀元, 画期的なでき事, 時代, 世

العربيه (Arabic)
‏(الاسم) دور, عهد‏

עברית (Hebrew)
n. - ‮עידן, מאורע חשוב‬

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