Computer servers and workstations have integrated real-time clocks that are based on simple, cheap, crystal oscillators. The real-time clock is battery backed and maintains system time even when the computer is switched off. However, crystal oscillators characteristics change significantly with temperature variation, which can cause the time to drift by several minutes each day. This article describes how Internet or Intranet based NTP servers can be utilised to maintain accurate time on a computer system.

NTP, or Network Time Protocol, was originally developed over 25 years ago as a means of distributing accurate time around the Internet. It is one of the oldest network protocols still in use today. NTP allows network time clients to synchronise to Internet based NTP time servers. It is an integral part of the Internet network structure.

Many operating systems including Microsoft Windows, LINUX, UNIX and Novell Netware integrate the ability to synchronise their system time by utilising NTP or its reduced sister protocol SNTP (Simple Network Time Protocol). Most NTP clients only require a single, or multiple, NTP server address to be specified and will periodically synchronise with the specified NTP server.

There a large number of Internet hosted NTP servers. Most synchronise with external timing reference such as GPS or time and frequency radio broadcasts. NTP servers that synchronise to an external timing reference are designated as stratum 1 time servers, this is because they sit at the head of the network time hierarchy. NTP servers that synchronise to stratum1 time server are designated stratum 2 and so on.

Below is a list of a small number of the most popular NTP servers available across the Internet. You should choose a NTP server close to you geographic locality, so as to reduce network round trip delays.

ntp.my-inbox.co.uk - Locality: United Kingdom. time.nist.gov - Locality: United States. canon.inria.fr - Locality: France. ptbtime1.ptb.de - Locality: Germany. clock.isc.org - Locality: Canada.

Most NTP servers are based on the LINUX operating system. The NTP software distribution is a freely downloadable application supplied under the GNU public licence. NTP source code and documentation can be obtained from the 'ntp.org' web-site. Under LINUX, NTP runs a daemon, periodically contacting specified NTP servers and synchronising system time.

Microsoft Windows operating systems utilise Microsoft's proprietary time synchronisation service 'Windows Time'. The Windows Time service can be configured via registry settings to synchronise with network time servers at specified intervals.

To conclude, Internet based NTP servers are readily available free sources of precise time. Additionally, most modern operating systems have the ability to contact and synchronise with NTP servers without the need for additional software. So, provided your network has an Internet connection, there is no longer any need to continue with inaccurate system time.