[ntp:questions] Accuracy of syncing with Internet time servers??

Richard B. Gilbert rgilbert88 at comcast.net
Fri Dec 1 03:19:18 UTC 2006


maruk2 at hotmail.com wrote:
> What is the accuracy of setting the time using WinXP time sync utility?
> 
> It lists two servers:
> time.windows.com
> time.nist.gov
> 
> I assume it is based on NTP. Does NTP take into account the
> transmission/network delay between

You assume wrongly!   It uses SNTP rather than the full NTP implementation.
> the server and my PC? Assuming the server itself is very accurate, is
> it possible to set the time of my PC to one millisecond?  What is the
> most accurate way to set the PC time? Are there any GPS devices that
> connect to a PC and can set the time to a single millisecond?
> 

If you want millisecond accuracy you need to run the Windows version of 
ntpd.  You will also need at least four internet servers that are near 
you in "net space".  If you are very lucky you can get within five or 
ten milliseconds of the correct time.  Better still would be a hardware 
reference clock such as a GPS timing receiver.

I run a ten year old Sun Ultra 10 workstation with a 440 MHz processor, 
ntpd V4.2, and a Motorola GPS Timing receiver and I get microsecond 
accuracy.  I could do the same with a PC though I wouldn't choose 
Windows as the operating system (Solaris X86 or Free BSD).




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