How to Maintain Accurate Time on Your PC
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.