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This item is from the PC Hardware FAQ, by Willie Lim and Ralph Valentino with numerous contributions by others. (v1.25).

2.46 How can I automatically set my PC's clock to the correct time?

[From: rbean@execpc.com (Ron Bean)]

A good place to start is http://www.eecis.udel.edu/~ntp/ which includes a lot of interesting time-related stuff for several operating systems, including ways to set your clock from time servers on the internet, or from dial-up modem services (long distance rates apply). Some will automatically reset your clock every time you connect to the internet. If you just want an accurate voice announcement, you can hear WWV by dialing (303)499-7111.

An alternative approach is to calculate how fast your clock drifts away from the correct time, and apply a correction factor. This method was popular before internet access was widely available, but has apparently been abandoned in recent years, even though it can be highly accurate.

I haven't found a Windows program that uses this method, but the DOS versions will run in a DOS window under Win95. These programs can be useful for machines that don't connect to the internet very often, but they can't be used with other clock-setting programs, because they need to keep track of exactly when the clock was reset. One free version is ADCLK100.ZIP, or several shareware versions can be found at the URL above.

Linux comes with a program called Clock(8) that takes this approach, although some people prefer to use the xntpd package instead. Type 'man 8 clock' for more information, or see the appropriate mini-HOWTO. Note: if you're running more than one OS on the same machine (such as Windows & Linux) you should only let one of them reset the CMOS clock, including the change to and from Daylight Savings Time.

GPS signals include time information, and some GPS receivers have a data connector. This may become the low-cost solution in the near future, as cheaper GPS receivers become available. For information on one version (designed by a Ham Radio club), see http://www.tapr.org/tapr/html/tac2.html

Several countries broadcast time signals by shortwave radio. Most radio clocks that will connect to a serial port cost $3-4000, but there are plans for an inexpensive "gadget box" (actually a 300 baud modem) that sits between your computer and any shortwave radio tuned to Canada's CHU on 3.33, 7.335, or 14.670 MHz (see ftp://ftp.udel.edu/pub/ntp/). If you're running some version of unix or NT, the xntpd package includes drivers for most radio clocks.

In Germany, the Physikalisch-Technische Bundesanstalt (PTB) broadcasts a coded time signal on 77.5 kHz from a transmitter near Frankfurt, and inexpensive receivers are available that can plug into a serial port. In the US, NIST runs a similar station (WWVB) on 60 kHz, but the data is encoded differently and receivers are expensive and hard to find.

You may have heard about Heathkit's "Most Accurate Clock", which decodes the time signal from WWV and has a serial port. Heath no longer sells kits, but they still sell the factory-built version of the clock (cost is in the $4-500 range). Their address is P.O. Box 1288, Benton Harbor, MI 49023.

NIST publishes a 30-page booklet (NIST Special Publication 432) that explains all of their time services in detail, including WWV, WWVB, and the GOES satellite service. It can be obtained from the Government Printing Office or directly from:

          NIST/Radio Station WWV
          2000 East County Road 58
          Fort Collins, CO  80524-9499

Of course, many people don't care what time it is anyway. But if your machine is on a network it can sometimes cause problems if it's too far out of sync from it's neighbors.

 

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