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The system clock of my PC (not a laptop) runs behind. What could be the cause?

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As alex said in the top answer, "consider marking the answer as accepted if you thought it was helpful. It benefits all of us :)" – Josh Hunt Sep 11 '09 at 8:48
Not really an answer but make use of ntp servers, there's a setting in Windows called "Sync time with internet servers". Use that and you time will always be accurate. – vava Sep 11 '09 at 12:49
up vote 15 down vote accepted

Your CMOS battery that maintains the BIOS (and clock) information could have run out. Change it, it is usually a CR2032 battery and really easy to swap out on your motherboard.

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This indeed did the trick. I looked at my motherboard's manual, where I found the type of the battery needed. And indeed, it was a common battery type (CR2032 like you said). Again, thanks for solving my problem. – Dimitri C. Sep 12 '09 at 21:26

Another potential cause not listed here is the RTC crystal is failing or not behaving.

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CMOS battery, bug in the OS, I have seen it under systems with a heavy load losing time. Possible when you run down the battery and it goes to sleep or hibernation you lose time. If it's a new laptop I wouldn't worry about the CMOS battery, just use NTP.

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Specifically use (or one of the country/regional sub-domains). Most OSs will query on a regular interval to keep things correct. – Richard Sep 11 '09 at 8:55

possibly a weak cmos backup battery?

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Is that on the motherboard? Do you think this can be replaced? – Dimitri C. Sep 11 '09 at 6:59
yes and easily - someone seems to have answered with a picture of it as well :) – Journeyman Geek Sep 11 '09 at 7:50

Check your reginal settings (double click on the clock in the taskbar). You may need to check if the daylight savings box is correct and that your laptop believes it is in the correct timzone.

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