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

Danny Mayer mayer at ntp.isc.org
Fri Jul 14 11:20:01 UTC 2006

Richard B. Gilbert wrote:
> NTP could do worse than to adopt the VMS 64 bit time format.  IIRC it
> was a count of 100 nanosecond "ticks" since some date in (I think)
> November 1857.

18 November, 1857 to be exact! See, I still remember!

  The format will represent any date-time from the base
> date through the next thirty thousand years or so.

Actually I think it was only to the year 8000 or something for some reason.

  Of course VMS
> updates the clock by adding 10,000 "ticks" at a time.  There is no
> documented or supported interface that will allow you to set or read the
> clock to greater than centisecond precision.  I've often thought that
> VMS Engineering should support a little greater precision;

At the time that was about as good as you could get. Don't forget that
VMS was originally designed in the mid-70's and first released in 1977.
Who could imagine that kind of precision in those days? And clocks were
not that good in those days. I remember working developing the clock
module tester for the Aquarius line (VAX 9000) at the end of the 1980's
and the precision that you could achieve was not that good at the time.

> Solaris can
> keep time to microsecond precision and even, with NTP, keep it
> accurately to that precision!

Solaris is modern in comparison.

> The current 64 bit NTP timestamp wastes some bits in picosecond
> precision.  I say "wastes" because even today's computers cannot
> exchange time without an uncertainty of two or three microseconds and
> those low order bits are meaningless noise.

That's for today. In 10 years that may very well not be true.


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