time-of-day clock


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time-of-day clock

[¦tīm əv ¦dā ‚kläk]
(computer science)
An electronic device that registers the actual time, generally accurate to 0.1 second, through a 24-hour cycle, and transmits its reading to the central processing unit of a computer upon demand.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

NTP

(Network Time Protocol) A TCP/IP protocol used to synchronize the real-time clock in computers, network devices and other electronic equipment. NTP is also used to maintain the correct time in Internet-connected wall and desk clocks.

The Coordinated Universal Time (UTC) can be obtained over the Internet from NTP time servers, or it can be acquired from stand-alone devices that receive atomic clock signals from the GPS. For more information, visit www.ntp.org. See UTC and time server.


Get the Time
Every time this Snom IP phone boots up, it gets the time from an NTP server.







Keep In Sync
SymmTime for Windows synchronizes a computer's real-time clock from NTP servers. It can display multiple time zones in digital and analog formats.







Out of Sync
This earlier LMCheck utility showed the time from all machines in the network. Computer clock circuits cost only a few cents and tend to drift (as in this example), which is why a network time server keeps every machine synchronized.







Synchronization Plus Security
For greater security, time servers such as this earlier SyncServer from Symmetricom obtained the time from the GPS rather than the Internet. (Image courtesy of Microsemi Corporation, www.microsemi.com)

real-time clock

An electronic circuit that maintains the time of day. It may also provide timing signals for time-shared operations. See NTP and BIOS.

UTC

(Coordinated Universal Time, Temps Universel Coordonné) The international time standard (formerly Greenwich Mean Time, or GMT). Zero hours UTC is midnight in Greenwich, England, which is located at 0 degrees longitude. Everything east of Greenwich (up to 180 degrees) is later in time; everything west is earlier. There are 42 time authorities around the world that are constantly synchronizing with each other. In the U.S., the time authorities are located at the U.S. Naval Observatory (USNO) and the National Institute of Standards & Technology (NIST). See NTP.
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