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From: (Norman Wilson)
Subject: [TUHS] Re: Happy birthday, Unix timestamp!
Date: Fri,  9 Sep 2022 14:53:06 -0400 (EDT)	[thread overview]
Message-ID: <> (raw)

Andrew Hume:

  if i recall correctly, V1 of Unix had time measured in milliseconds.
  were folks that sure that this would change before wrap-around?


Not milliseconds (which were infinitesimally small to the
computers of 1969!) but clock ticks, 60 per second.

Initially such times were stored in a pair of 18-bit PDP-7
words, giving a lifetime of about 36 years, so not so bad.

The PDP-11's 16-bit words made that a 32-bit representation,
or about two and a quarter years before overflow.  Which
explains why the time base was updated a few times in early
days, then the representation changed to whole seconds, which
in 32 bits would last about as long as 36 bits of 60 Hz ticks.

The PDP-7 convention is documented only in the source code,
so far as I know.  The evolution of time on the PDP-11 can
be tracked in time(II) in old manuals; the whole-seconds
representation first appears in the Fourth Edition.

Norman Wilson
Toronto ON
Not that old a timer, but once looked into old time

             reply	other threads:[~2022-09-09 18:53 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-09 18:53 Norman Wilson [this message]
  -- strict thread matches above, loose matches on Subject: below --
2022-09-09 12:06 Douglas McIlroy
2022-09-09 17:16 ` Andrew Hume
2022-09-08 22:28 [TUHS] " Dave Horsfall
2022-09-08 23:48 ` [TUHS] " Rob Pike
2022-09-09  0:11   ` Dan Cross
2022-09-09  4:24   ` Rob Pike
2022-09-11  0:09   ` Dave Horsfall
2022-09-09  3:29 ` Seth Morabito
2022-09-09  7:03   ` Michael Kjörling

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