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.


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

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

Keep In Sync
Symmetricom's SymmTime synchronizes your computer's real-time clock from any NTP server around the world. You can also display multiple time zones in a variety of digital and analog formats. To download this nifty program, visit www.ntp-systems.com.

Out of Sync
When you run Symmetricom's LMCheck utility, which displays the time from all machines in the network, you'll be hard pressed to find any two that are truly in sync. Desktop computer clock circuits cost only a few cents and tend to drift, which is why a network time server is required to keep every machine synchronized. To download LMCheck, visit www.ntp-systems.com (LMCheck uses a LAN Manager function, hence the LM).

Synchronization and Security
Time servers are stand-alone devices that obtain and distribute the correct time to all machines in the network. This SyncServer from Symmetricom offers maximum security. It uses the GPS to get the time without having to keep a TCP/IP port open to hackers via the Internet. It is also offered with a rubidium atomic clock that keeps rock solid time when the GPS signals are not available. (Image courtesy of Symmetricom, Inc., www.symmetricom.com)

real-time clock

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


(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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