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[MD1] HFS+ and Daylight savings

From: (MW Ron)
Subject: Daylight Savings Time & Mac OS Extended Volumes

Projects built with CodeWarrior that are stored on a HFS+ volume will be
rebuilt after Daylight savings time is changed…….


Mac OS 8.1: Daylight Savings Time & Mac OS Extended Volumes

I notice that when I check Daylight Saving Time in the Date & Time control
panel, both the creation and modification times of files on a Mac OS
Extended volume change by one hour.If I change the time by hand, the times
do not change. Times on HFS volumes don’t change either. What is going on?

The reason the times change is that Mac OS Extended stores the creation and
modification times in GMT time. The offset from GMT is stored in PRAM. This
value is added to the time stored for the file to determine the correct
creation or modification time.The GMT offset is stored when you select a
time zone in the Date & Time control panel. This offset is modified when
Daylight Saving Time is checked. Since the value is stored as seconds, 3600
is either added to or subtracted from the GMT offset depending upon whether
entering or exiting Daylight Saving Time, respectively.For example, a file
was created at 12:00 PM Pacific Standard Time. The value stored was 8:00 PM
GMT since there is an 8 hour difference. When Daylight Saving Time is in
effect, the difference is only 7 hours. This causes the creation time of
the file to be displayed as 1:00 PM PST, not 12:00 PM.Changing time zones
will also affect the creation and modification dates.Drawbacks of this are
that aliases may break and incremental backups may become full backups
since every file appears to have been modified.

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