How To Synchronise Your PC's System Time

PC's keep time, even when the computer is turned off,is required is local access to an accurate time
using battery-backed real time clock (RTC) chips. Thereference. However, there are many freely available
RTC chips are mass-produced low-cost componentstime and frequency resources that can be utilsied.
that generally do not have good time keepingA number of national radio time references are
properties and have a tendency to drift. This articletransmitted free-to-air. These radio broadcasts are
discusses a number of ways to maintain accurategenerally referred to by their 'call sign'. WWVB is the
time on a PC. It also provides information on how toNorth-American time and frequency radio transmission,
synchronise a PC's time with precise Internet andbroadcast for Colorado in the States. DCF is the
national time and frequency radio transmissions.call-sign of the German radio time transmission, which
Computer systems time can drift anything from a fewis broadcast from Meinflingen near Frankfurt. The UK
seconds a day to a few minutes each day. Whentime transmitter is located at Anthorn, Cumbria, it's call
processing transactions or performing time criticalsign is MSF. A number of other broadcasts are
tasks across a number of computers, incorrect timeavailable in France, Canada, Switzerland and Japan.
can be a real headache.USB and serial radio receivers are available that can
The Internet solved this problem by introducing thereceive radio time broadcasts and provide computers
Network Time Protocol (NTP). NTP can be used towith accurate timing information. The PC system time
distribute accurate time from a highly precise timecan then be synchronised to the received time and
server to network time clients. Most modern operatingfrequency radio source.
systems have the ability to synchronise time with aThe disadvantage with National radio time and
NTP server. Generally, all that is required is the IPfrequency solutions is that they have a finite
address or domain name of Stratum 1 or Stratum 2transmission range. Their transmissions are generally
NTP servers.regional and limited to national boundaries. The Global
LINUX and UNIX operating systems can download thePositioning System (GPS) provides a solution to this.
full NTP implementation from the NTP web siteThe GPS system operates from a number of orbiting
'ntp.org'. NTP is freely available open source softwaresatellites. Each satellite has an on-board highly accurate
available under the GNU public licence.synchronised atomic clock. GPS can provide highly
Microsoft Windows XP/2000/2003 and Vistaprecise timing information anywhere on the face of the
operating systems have an integrated SNTP client.planet. All that is required to receive the GPS
SNTP stands for Simple Network Time Protocol.transmissions is a low-cost GPS receiver and antenna.
Simple Network Time Protocol provides a sub-set ofThe GPS antenna needs to be shown a good clear
the Network Time Protocols algorithms. SNTP doesview of the sky for correct operation. By connecting a
not include many of the complex algorithms availablePC to a serial or USB GPS receiver, accurate timing
to NTP to filter time and maintain high precision.information is continuously available.
Windows operating systems allow an IP address orTo summarise, a wide range of highly accurate
domain name of a Internet or Intranet NTP server tocomputer timing references are freely available. Utilising
be entered in the time properties tab. The SNTP clientthe Internet, National time and frequency radio
will then periodically contact the NTP server in order totransmissions or the GPS system can ensure that a
update and synchronise system time.computers time remains locked to a precise time
A problem arises, however, if the computer does notreference.
have access to the Internet or is not networked. What