First computer with real-time clock?

From: David V. Corbin <>
Date: Tue Aug 3 10:01:22 2004


The system I was working on was rack-mount...on a submarine [NATO Walrus
Class - launched circa 1984]

I completely agree that there were other more accurate sources [of which
youy name a few. I should have been more precise in my statement.
I was comparing it to other board mountable electronic clock sources [since
we were discussing crystals].

The system in question actually connected to a highly accurate 1PPS External
source that was slaved to a radio clock under normal circumstances. However
our rack need to maintain time even in the event of external failures. It
was deemed that a <50mS error per day under error conditions was acceptable.


>>>>> I was involved in the development of soms Military
>>>>> systems [1979-1983] that used a tempe0rature
>>>>> stabilized crystal with 0.5ppm stability. To the
>>>>> best of my knowledge this was a "state of the art"
>>>>> implementation of automomous time keeping for 1979.
>>> 0.5 ppm for boxes that get carried around in military
>>> trucks and bounced around in the field -- that's quite
>>> good. For something that's sitting in a reasonably
>>> controlled environment, that's not so great;
>>> I think that 10^-8 would be considered state of
>>> the art for OXCOs (1970s or not).
>>> For autonomous timekeeping independent of technology, the
>>> state of the art was a second per year or so (that's 10^-8,
>>> roughly) around the early 1900s. First with pendulum
>>> clocks (Shortt clock), then around the 1940s or so crystal
>>> clocks came in that could match this. And not too long
>>> after that there came the rubidium (10^-10) and cesium
>>> (10^-14) clocks. Some of that would be found in military
>>> gear, I think (Rb at least, Cs somewhat less likely).
>>> Consider GPS satellites, which have either or both built-in.
>>> paul
Received on Tue Aug 03 2004 - 10:01:22 BST

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