[ntp:questions] Re: Windows timekeeping - sudden degradation - why?

John Allen allen{at}vo{dot}lu at ntp.isc.org
Wed Dec 14 21:58:07 UTC 2005

John Allen wrote:
> Richard B. Gilbert wrote:
>  >My guess would be that your local clock has a frequency error well in
>  >excess of 500 parts per million!   If that is the case, you will
>  >probably have to replace the mother board to fix it.

> As you say, the hopeless inaccuracy of the system clock might be cured 
> only by a new motherboard, although it seems strange that for more than 
> a year it seemed to work fairly well.

I really was going to give up on this when I made what could be a useful 
discovery. While reading of recurrent problems with system clocks on nForce2 
motherboards, eg these threads:

I found references to possibly using a different HAL (Hardware Abstraction 
Layer). I then did what was probably not wise, which was to change from
"ACPI Uniprocessor PC" to "Advanced Configuration and Power Interface (ACPI) 
PC". I also set the BIOS option "FSB Spread Spectrum" to "disabled".

By good fortune this did not stop the PC working but it has had the result that 
the system clock has been very stable for 24 hours and NTP is now working 
properly, with offsets of no more than 7 ms (from the NTP server on my LAN) over 
long periods:

 >ntpq -c "rv 0"
assID=0 status=4644 leap_add_sec, sync_ntp, 4 events, event_peer/strat_chg,
version="ntpd  2004 May 07 8:37:39  (1)"?, processor="unknown",
system="WINDOWS/NT", leap=01, stratum=4, precision=-20,
rootdelay=58.614, rootdispersion=153.312, peer=7996, refid=,
reftime=c74ae7bc.223db21c  Wed, Dec 14 2005 19:49:32.133, poll=9,
clock=0xc74ae8e7.5bfd448c, state=4, offset=-7.045, frequency=-7.005,
noise=3.010, jitter=0.955, stability=1.529

It may be that this HAL change only works because it disables the APIC (Advanced 
Programmable Interrupt Controller); at any rate, it has made me realise how far 
one can go from what initially appeared to be an NTP issue.

I've noticed that some other threads in this newsgroup have concerned PCs with 
nForce2 motherboards, so this could be a useful hint. However, changing HALs 
should not be done without careful reflection and a willingness to reinstall 
Windows if something goes wrong.

This site (in German) gives some more information:

as does this:

Moral of the story: if NTP seems to stop working properly and you have an 
nForce2 motherboard (a) the problem is quite possibly not NTP and (b) you may 
not need a new motherboard...



John Allen
Bofferdange, Luxembourg

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