[ntp:questions] Re: NTP4 has 3 different time formats! Namly (32, 64, 128) bits wide

Richard B. Gilbert rgilbert88 at comcast.net
Mon Jul 17 04:42:44 UTC 2006

David L. Mills wrote:

> Richard,
> I can't claim preconition, as the current NTP timestamp format was 
> invented in 1978 when nominal accuracies were in the 16-ms range. 
> However, the resolution limit of 232 picoseconds is likely to be 
> exceeded when the CPU clock rate approaches 4 GHz, which might not be 
> long off.

I suppose that even a 2 GHz machine could slice time into 500 picosecond 
increments.  But I was thinking in terms of the ability to set a clock 
that accurately.  There's no way that I can think of that it could be 
done over a network using today's technology.  I'm seeing a ~4us delays 
on my 100 Mb full duplex LAN.  I think that means I can't pass time from 
  machine A to machine B over my LAN without an uncertainty of ~2us. 
The error is probably less than that but probably is the best we can say.

So you could get delta time measurments with 232 picosecond resolution 
but getting absolute time accurately with that precsion is not going to 
be easy.

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