JSI Tip 4747. How is the time on a Windows XP computer synchronized?

W32Time will periodically check its local time with the current time by connecting to the time source, generally the authenticating domain controller.

Starting during system startup, W32Time attempts synchronization every 45 minutes, until the clocks have successfully synchronized three times, after which 8 hour intervals are used. If there is a failure to obtain a timestamp, or a validation failure, the process starts over.

W32time uses the following algorithm:

If the local clock time of the client is behind the time received from the time source, W32Time will change the local clock time immediately.

If the local clock time of the client is more than three minutes ahead of the time source, W32Time will change the local clock time immediately.

If the local clock time of the client is less than 15 seconds ahead of the time source, W32Time will halve the clock frequency for long enough to bring the clocks into sync.

If the local clock time of the client is 15 seconds or more ahead of the time source, W32Time will quarter the clock frequency for long enough to bring the clocks into sync.

NOTE: The amount of time that the clock spends running at an unusual frequency depends on the size of the offset that is being corrected.

The standard MaxClockRate is 100144 and it is located at HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeConfig.