Cuckoo Clocks to NTP Servers: Accuracy in Timekeeping

The clock in its form that we recognise today has been around since the middle of the fourteenth century. Before then, measuring the passage of time had always been a tricky affair with the movement of the sun being the only reliable method of time-telling and the only clocks being crude sundials or water clocks.

Most computers have internal clocks which are battery backed, so the computer can still keep time when the machine is off. However, are these clocks really that reliable? The answer of course is no.

Computers are mass marketed and designed for multi functions, timing not being that high on the manufacturer's agenda. The internal clocks (called RTC real time chips) are normally adequate for home computing or when workstations run alone. However, when computers run in a network, then a lack of synchronisation can cause problems.

It may be a minor thing such as an email arriving somewhere before it was sent (according to a PC clock) but with some time sensitive transactions and applications, a lack of synchronisation can cause imaginable problems: Imagine turning up at an airport only to find the airline seat you had bought weeks before was in fact sold to somebody else afterwards as their booking agent had a slower clock on their computer!

To get around these problems most computers on a network are synchronised to a single time source using NTP (network time protocol) this time source can be either relative (a computer's clock or wrist watch) or an absolute time source like UTC.

UTC (Coordinated Universal Time) was developed after the emergence of atomic clocks and is a standard time scale used globally, allowing machines all over the world to use a single time source.

Windows XP can easily set the system clock to use UTC by accessing an Internet source for UTC (either: time.windows.com or time.nist.gov). To achieve this, a user merely has to double click the clock on their desktop and adjust the settings in the Internet Time tab.

However, Microsoft and other operating system manufacturers strongly advise that external timing references should be used as Internet sources can't be authenticated, making systems vulnerable to a malicious attack.

If you wish to run a network time server Windows XP, then a specialist NTP server are available that can receive a time reference via the GPS satellite system or specialist national transmissions

To allow Windows XP to operate as a network time server, the NTP service needs to be switched on. To activate NTP simply find the following subkey in the registry editor (regedit):

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpServer\ Right click enabled (in the right-hand window) then Modify. Edit the DWORD Value and type 1. Right-click NtpServer, then Modify and in the Edit DWORD Value under Value Data type Peers, then click OK.

Exit the registry and start windows time service by clicking Start/Run and typing: net stop w32time && net start w32time.; Then on each computer on the network (other than the domain controller which can't be synchronised with itself) type: W32tm/resync/rediscover.