[ntp:questions] Clock skew changes drastically between reboots

Spoon root at localhost.invalid
Sun Apr 1 18:44:38 UTC 2007

Hello everyone,

I've noticed something I find very strange on the systems I have to work 
with. Every time I reboot the computer, the clock skew of the local 
clock changes, sometimes by what seems to be a huge amount.

For example, I boot the computer, let ntpd run for 12 hours, and the 
value recorded in the drift file is 35 ppm. I reboot the computer, let 
ntpd run for 12 hours, and I get 5 ppm...

The temperature in the room did not change much. Could the operating 
system (Linux be responsible for this? Could the 
motherboard supply a different voltage every time I reboot the system?

How much is the system clock in a PC affected by temperature? I've read 
2 ppm per °C, or was it 0.5 ppm per °C? How much is it affected by 
voltage? What other parameters have an influence?

When I say "system clock" I think that, on this system, Linux uses the 
PIT on the motherboard, but I'm not 100% sure.


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