Using Mac OS 8.1 on a Mac OS Extended hard disk with Daylight Saving Time selected in the Date & Time control panel, both the creation and modification times of files change by one hour. However, when using Mac OS 8.1 on a Mac OS Standard format hard disk, the times do not change.

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 on whether entering or exiting Daylight Saving Time.

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 also affects the creation and modification dates.

Drawbacks of this are that aliases may break, and backups may be effected.

Note: This issue has been addressed in Mac OS 8.5 and later and no longer occurs.