From: firstname.lastname@example.org (Norman Wilson)
Subject: [TUHS] Re: Happy birthday, Unix timestamp!
Date: Fri, 9 Sep 2022 14:53:06 -0400 (EDT) [thread overview]
Message-ID: <45225B8CFC8D9179CB02A21EF7638288.email@example.com> (raw)
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.
Not that old a timer, but once looked into old time
next 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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