[time-nuts] Selecting server hardware (newbie question)

Hal Murray hmurray at suespammers.org
Tue Jan 31 04:32:33 EST 2006

phk at phk.freebsd.dk said:
>>Most systems use the 32 KHz battery backed TOY (Time-of-Year) clock
>> for timekeeping rather than the CPU crystal. 

> Wrong, few systems do.   Most systems use the 32.768 kHz xtal to run
> their battery-backed Real Time Clock, but this is only consulted on
> boot to get an initial fix on time.

Thanks for the heads up.

>>This is good because it's generally farther from the heat
>> generating CPU than the CPU crystal.

> This has no hold in reality. 

It's not what I was expecting.  Several years ago, I was trying to match the 
temperature of the crystal with the observed drift.  The data looked a lot 
better after Dave Mills pointed out that I was measuring the temperature of 
the wrong crystal.

I think he said it was done that way in order to support SMP systems.  I'm 
pretty sure it works that way on this old Linux box.  I probably jumped to 
the conclusion that it was more common than it is.

Anybody got a list of which systems use which crystal?

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