[LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?

[Poul-Henning Kamp]

In message <20140109110353.35874406063 at ip-64-139-1-69.sjc.megapath.net>, Hal Mu
rray writes:


>The IBM 360 systems starting in 1964 used the power line frequency.  (A 

>location in low memory got bumped at 300 counts per second.  5 per cycle on 

>60 Hz and 6 per cycle on 50 Hz.)  I wonder how much the power timekeeping 

>wandered back then relative to today.


It used to be pretty good, because people used synchronous motors to drive
clocks so the power companies tried to keep the long-term frequency
correct.

In Denmark they usually lost a couple of seconds during the day and
gained them back during the night, similarly they lost half a minute
over winter and gained it back over summer.

After deregulation nobody gets paid to keep the long term frequency,
so mains is no good, actually down-right bad, for timekeeping anymore.

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Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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