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* [TUHS] Happy birthday, Unix timestamp!
@ 2022-09-08 22:28 Dave Horsfall
  2022-09-08 23:48 ` [TUHS] " Rob Pike
  2022-09-09  3:29 ` Seth Morabito
  0 siblings, 2 replies; 10+ messages in thread
From: Dave Horsfall @ 2022-09-08 22:28 UTC (permalink / raw)
  To: The Eunuchs Hysterical Society

https://www.timeanddate.com/on-this-day/september/9

``Unix time or Unix epoch, POSIX time or Unix timestamp, is a time system 
  that measures the number of seconds since midnight UTC of January 1, 1970, 
  not counting leap seconds. At 01:46:40 UTC on September 9, 2001, Unix time 
  reached the billionth second timestamp.''

Hard to believe that it was that long ago...

-- Dave

^ permalink raw reply	[flat|nested] 10+ messages in thread
* [TUHS] Re: Happy birthday, Unix timestamp!
@ 2022-09-09 12:06 Douglas McIlroy
  2022-09-09 17:16 ` Andrew Hume
  0 siblings, 1 reply; 10+ messages in thread
From: Douglas McIlroy @ 2022-09-09 12:06 UTC (permalink / raw)
  To: TUHS main list

> Well, you can imagine what happened when the leading digit changed
> from an ASCII "9" to an ASCII "1". Oops.

I first saw a time-overflow bug more than 60 years ago. Accounting
went haywire in the Bell Labs' comp center on day 256 of the year,
when the encoded output of a new time clock reached the sign bit.

Doug

^ permalink raw reply	[flat|nested] 10+ messages in thread
* [TUHS] Re: Happy birthday, Unix timestamp!
@ 2022-09-09 18:53 Norman Wilson
  0 siblings, 0 replies; 10+ messages in thread
From: Norman Wilson @ 2022-09-09 18:53 UTC (permalink / raw)
  To: tuhs

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

^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2022-09-11  0:09 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-08 22:28 [TUHS] Happy birthday, Unix timestamp! 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
2022-09-09 12:06 Douglas McIlroy
2022-09-09 17:16 ` Andrew Hume
2022-09-09 18:53 Norman Wilson

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