Many computer systems keep very poor time. Often this is due to the low quality of the timing components utilised by the computer. In order to maintain low-cost, inferior timing components are utilised. However, there a number of hardware and software solutions to maintain precise time. This article discuses how GPS and radio based hardware clocks and Internet NTP servers can be used to provide a solution to computer time synchronisation.



There are a number of commercially available hardware time references that utilise GPS or National radio time and frequency broadcasts to maintain accurate time on computers. These hardware clocks generally have serial or USB interfaces that provide regular time updates. Software drivers constantly reads precise timing information from the hardware timing reference in order to maintain accurate system time. More sophisticated software may be available that provides a software interface between the hardware clock and the NTP software distribution. This allows a PC to be configured as a precise stratum 1 NTP server.

GPS hardware clock systems have a number of advantages. They are generally highly accurate providing timing precision to within nanoseconds of UTC. GPS is a global system that works anywhere on the face of the planet, provided the antenna can be provided with a good view of the sky. Radio based hardware clocks are generally less accurate and can only be received within the locality of the radio transmitter. However, they do have the advantage that generally a good signal can be received indoors close to the host computer. GPS clocks require an antenna with a good view of the sky, which can be impractical for many installations.

The Internet has developed precise timing algorithms to maintain accurate time on client computers. The Network Time Protocol (NTP) was developed over 25 years ago just to fulfil such a requirement and is now the dominant method of time synchronisation across a computer network. Many operating systems such as Microsoft Windows 2000, 2003, XP, LINUX, UNIX and Novell have adopted the NTP standard. There are a vast number of highly precise Internet NTP server systems that can be utilised free of charge to provide accurate computer time synchronisation.

Microsoft Windows 2000 and 2003 server operating systems provide a pre-installed SNTP (Simple Network Time Protocol) client that can synchronise to any NTP server. The Windows 2000/2003 Server SNTP time client is called 'Windows Time'; it runs in the service list and is configured by editing registry entries. Windows XP also has an integrated SNTP client that is configured from the 'Time Properties' applet in the control panel.

LINUX has developed much more complex timing algorithms in order to maintain highly accurate time. NTP was originally developed for the LINUX operating system and provides complex timing algorithms to provide a highly precise timing solution. The NTP software distribution is freely available and downloaded under the GNU public licence. Configuring NTP to utilise an external hardware reference clock provides a local stratum 1 NTP server for use on an intranet.

SNTP was originally developed to run on small computers and microcontrollers without the computing power required to run full-blown NTP. SNTP provides much of the functionality of full-blown NTP without the more sophisticated algorithms. The Windows 2000/2003 Server operating systems utilise SNTP to provide network wide time synchronisation of its Kerberos authentication protocol. SNTP allows a client to synchronise to a NTP server but with some loss of precision.

To conclude, NTP is utilised throughout the internet as a standard way of synchronising computers and network infrastructure to the precise time. Client computers can maintain synchronisation to within milliseconds of the correct time. GPS and radio hardware clocks can provide accurate synchronisation of computer systems that have no access to the Internet or to provide a Stratum 1 NTP Server resource.