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Content

PC Clock Drift, introduction
Perhaps you thought that due to that you synchronize your PC clock against a timeserver (Atomic Clock) you always have the right time. Not correct, between your synchronization to the timeserver you have a clock drift that can be rather significant. At the point of synchronization with the timeserver, you have the right time (with a resolution depending on the timeserver, lag time on the Internet and the constraints given by the preemptive multitasking technique used by the Win32 operating system).

However, the inherent clock drift will shortly offset the correct time. PC clocks are notorious known for there quit large drifts. It doesn’t matter much what type (Vendor) of motherboard you use. We have measure some motherboards that have hade drifts up to 10 minutes per 24 hour. In that case it was also a most well-known manufacture of the PC.

Below you have a figure that shows what happens. As you can see the clock, drifts away from the correct time (negative drift in this case). At the time of synchronization with the timeserver, the clock is reset to the correct time (zero offset). But the inherent drift of the clock immediately starts to offset the clock from the correct time. You have to wait to the next sync with the timeserver before the clock is set to the correct time again. And so it goes on. A solution is of course to synchronize more frequently. But that is not a perfect solution and consumes a lot of unnecessary bandwidth.



A better solution is to “Tweak” the clock. This can be done by computing the drift coefficient and apply a change to the clock rate in the hardware layer of the clock. By using this method, you can change the drift to close to zero. In the figure below, you can see how it works.



As you can see the drift is close to zero after that, the “tweak” of the clock has been applied. This also means that you no longer has to do a frequent synchronization with the time server to keep the right time.

To check your clock Spectron has developed a free application called “Spectron Time Drift Utility”. You can download this utility to check your clock drift on your own PC. You can also see what happens when you “Tweak” the clock to eliminate the drift.

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