In a recent note, Charles Mills said:
> Date: Thu, 10 Nov 2005 15:27:16 -0500
>
> > Yes, definitely set it to GMT.
>
> Can you or anyone else provide a reference to a Redbook or other IBM
> document to back up the assertion that setting the TOD clock to GMT or UTC
> was IBM's design intention or recommended practice?
>
For example, in:
# 7.5.127 "z/Architecture Principles of Operation"
4. The following chart shows the setting of bits 0-63 of the STORE
CLOCK EXTENDED operand for 00:00:00 (0 am), UTC time, for several dates:
January 1, 1900, January 1, 1972, and for that instant in time just
after each of the 22 leap seconds that have occurred through January,
1999. Each of these leap seconds was inserted in the UTC time scale
beginning at 23:59:60 UTC of the day previous to the one listed and
ending at 00:00:00 UTC of the day listed. ...
One might argue that UTC was an arbitrary choice, merely for the
printed example. I, however, find it significant that they
chose for their example to show a TOD clock set to UTC (roughly;
actually TAI-10), rather than to Poughkeepsie local civil time.
o The merits of using a reference that doesn't need to be changed
twice a year have been well advanced in this thread.
o Leap seconds happen. There are similar benefits, however smaller
to using a reference that doesn't need to be reset at leap seconds.
-- gil
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