Double summer time?

[Wolfgang S. Rupprecht]

Timothy Murphy <tim at birdsnest.maths.tcd.ie> writes:
> Wolfgang S. Rupprecht wrote:
>
>> This is why one really wants to run the pc in UTC.
>
> I've never really understood this question asked during installation:
> "Does your computer use UTC" (or something like that).
> How does one determine the answer?

That question could be worded much better.  It is really asking you if
you *want* to use UTC.

Unix, BSD and, I believe, Linux has traditionally always used UTC
internally and then as part of the display code adding in the timezone
and DST offsets.  Other operating systems of the time like DEC VMS and
Microsoft DOS used local time at their lowest levels.  This always
caused problems for the code when traveling across timezones or when
rebooting during the hour of DST transitions.  Elaborate (and poorly
performing) hacks were constructed to compensate for double DST
transitions.  These hacks of course can't compensate for two
non-cooperatin OS's both trying to be helpful and changing the time.
That case just can't be fixed.  The only choice is to use the
traditional and simpler constant UTC in the clock chip and let the
OS's that are smart enough do all timezone and DST adjustments during
display.

(And for completeness linux does keep the kernels time in UTC no
matter what the checks for that box.  The problem is that the kernel
has to apply a reverse timezone/DST shift whenever it reads the clock
chip and it has to step the time in the clock chips whenever the DST
transitions occur.)

-wolfgang
-- 
Wolfgang S. Rupprecht                http://www.wsrcc.com/wolfgang/