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

Danny Mayer mayer at ntp.isc.org
Sat Jul 15 22:15:24 UTC 2006

David J Taylor wrote:
> Danny Mayer wrote:
>> 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!
> I often wondered why that base was chosen - something to do with the 
> Smithsonian?

Oops, I'm off by a year, it's 1858. From this URL if you want all of the
details: http://vms.tuwien.ac.at/info/humour/vms-base-time-origin.txt

"So why 1858? The Julian Day 2,400,000 just happens to be November 17,

The Modified Julian Day was adopted by the Smithsonian Astrophysical
Observatory (SAO) in 1957 for satellite tracking. SAO started tracking
satellites with an 8K (non-virtual) 36-bit IBM 704 computer in 1957,
when Sputnik was launched. The Julian day was 2,435,839 on January 1,
1957. This is 11,225,377 in octal notation, which was too big to fit
into an 18-bit field (half of its standard 36-bit word). And, with only
8K of memory, no one wanted to waste the 14 bits left over by keeping
the Julian Day in its own 36-bit word. However, they also needed to
track hours and minutes, for which 18 bits gave enough accuracy. So,
they decided to keep the number of days in the left 18 bits and the
hours and minutes in the right 18 bits of a word."


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