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How to Maintain Accurate Time on Your PC

by David Evans

PC's have internal real time clocks designed to maintain system time. The internal clocks rely on relatively low-cost crystal oscillators, which are notoriously inaccurate. In many cases PC system time can drift by several minutes each day. This article describes various methods of maintaining a highly accurate time on your PC. It describes how to utilize Internet time references, radio and GPS clocks and dedicated NTP server systems.

Internet Time References

The Internet utilizes the Network Time Protocol to distribute accurate time information to network time clients. NTP has been an important part of the Internet for over 25 years. The protocol was born through the need to provide synchronization of time critical processes across the Internet.

Most modern operating systems, including Windows XP, 2003 and LINUX have the ability to synchronize time with a NTP Server. There are a host of Internet based NTP Servers with public access that can be used to synchronize your PC. Below is a list of popular Internet based public access NTP Server references:

time.nist.gov - US based time reference.
ptbtime1.ptb.de - German time reference.
ntp.my-inbox.co.uk - UK time reference.
canon.inria.fr - French time reference.
clock.isc.org - Canadian time reference.

Windows XP has pre-installed SNTP client software that can synchronize time with a NTP server. This is achieved by simply entering the domain name of an Internet NTP Server in the time properties tab. The host computer will then periodically contact the NTP Server and synchronize the system time to the specified reference.

Linux and Unix systems have the NTP software distribution available from the NTP website, ntp.org. The NTP application runs as a daemon, constantly monitoring specified NTP servers. The application reads a list of NTP servers from a configuration file, 'ntp.conf', and periodically synchronizes time. A list of NTP server references is specified with the 'server' configuration command thus:

server time-a.nist.gov # NIST, Gaithersburg, Maryland NTP server
server time-c.timefreq.bldrdoc.gov # NIST, Boulder, Colorado NTP server

Once configured, the NTP daemon can be started, stopped and restarted using the commands: 'ntpd start'; 'ntpd stop' and 'ntpd restart'.

Radio and GPS Clock Timing References

There are many commercially available radio and GPS clock timing references for PC's. Radio and GPS clocks obtain accurate time from national radio timing references or from the GPS system. The devices have serial or USB interfaces and provide an accurate timing reference to PC's. Driver software periodically synchronizes the system time of the host computer to the received reference time. Often reference clock drivers are available that interface to the NTP application software to provide your own dedicated NTP server.