[ntp:questions] What level of timesynch error is typical on Win XP?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Fri Oct 22 15:23:19 UTC 2010

"Evandro Menezes" <evandro at mailinator.com> wrote in message 
news:2dd44831-09a6-4cf5-ac15-acc8ef6b05b0 at t20g2000yqa.googlegroups.com...
> Yes, except that Windows ends up raising the effective priority of
> system tasks that supersede NTP's effective priority.  Among the worst
> offenders, network DPCs and some disk DPCs with some anti-virus
> programs (i.e., Mcafee).
> Then, even tasks with real-time priority will and do get starved and
> an algorithm like NTP's, which has hard deadlines, suffers, thus the
> inherently higher jitter in Windows.

Thanks, Evandro.

That could explain why I see higher NTP jitter on a Windows system running 
a USB network source (digital video data stream) than receiving a similar 
data stream on a PCI card under either Windows XP or Windows-7.  I guess 
it will depend on how well the DVB network component is written.  This is 
comparing PC Gemini (graph scale +/- 100ms) compared to PC Hydra (graph 
scale +/- 3ms) here:


(BTW: I can't use the PCI card in the Vista system as the ASUS A8N SLI 
deluxe motherboard will, apparently, blow power tracks if the PCI card is 
used.  I don't propose to test that!).

Having said that, anyone with such time-critical requirements will want to 
stop all non-essential and any unpredictable processes such as anti-virus 
or system updates and virus scans.  On Windows-7 that can be quite a 
challenge compared to Windows XP.


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