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Legacy Information: Daylight Savings, Standard Time & Reported File Times

2021-Feb-26: Information on this page is presented for legacy purposes. The issue referenced here - file dates in two paths going out of synch at daylight savings time changes - is largely at thing of the past thanks to much more reliable and predictive time zone mangement settings in Windows 10.


Directory Toolkit users may find that path comparisons between two computers suddenly show a difference in file times even though no changes were made to the files in either path following a changeover to/from "Daylight Savings" or "Standard Time".

This behavior is because:

1. The two computers physically reside in different time zones.

2. The Time Zone settings on the computers are not set to the same time zone

3. Time Zone & "Daylight Savings" rules differ between the two computers. In most cases this is because the default Daylight Savings rules for one or both computers has been changed from the default.

4. One of the paths being compared is FAT32 or is using old/now-outdated driver software (e.g. CDROM drive or USB drives).

This behavior is not a bug in Directory Toolkit!

Differences in reported file times happens because the Windows operating system (XP and above) automatically adjusts reported file time based on "Universal Coordinated Time (UTC)" AND the Daylight Savings rules and Time Zone in effect for the computer. Assuming the paths being compared are on computers located in the same time zone, if the operating system returns an incorrectly "adjusted" file time, Directory Toolkit will then display file times that are different even though the two paths were previously identical.

By way of example, the table below from the Windows 98 era depicts the impact of the automatic Windows "Daylight Savings Adjustment" on reported file times for a test file created on March 27 at 03:00am (USA Eastern) under US English Windows 98. The file was then copied to a Windows 2000 machine (FAT32 partition) and a Directory Toolkit comparison of the two paths was made. The computer dates were then changed on the two computers as per the conditions below. The NT 2000 machine was configured to "Automatically Adjust for Daylight Savings".

Reported File Time Stamp and Daylight Savings Compensation

 

MS-DOS

 

Explorer

 

Directory Toolkit

Condition

Win98

Win2000

Win98

Win2000

Win98

Win2000

1

3:00am

3:00am

3:00am

3:00am

3:00am

3:00am

2

3:00am

3:00am

3:00am

4:00am

3:00am

4:00am

3

3:00am

3:00am

3:00am

3:00am

3:00am

3:00am

4

3:00am

3:00am

3:00am

2:00am

3:00am

2:00am

Condition - Date settings for the 2 machines

#1 - Win98 Machine = 03/27,  Win2000 Machine = 03/27
#2 - Win98 Machine = 06/27,  Win2000 Machine = 03/27
#3 - Win98 Machine = 06/27,  Win2000 Machine = 06/27
#4 - Win98 Machine = 03/27,  Win2000 Machine = 06/27

Note that the differences in the reported file times above. The Windows 98 machine did not make Daylight Savings compensations in the reported file times, hence the file times reported by that machine for files that reside on that machine never change.

In the Windows 10 era situations lke the above are largely a thing of the past. 

If you do have issues, we suggest:

1) Make sure all machines are set to the correct time zone for their location. On Windows 10, Settings -> Time and Language -> Date & Time is the best starting point. Search https://support.microsoft.com/ for 'Time and Date' for officlal guidance.

2) Enable 'Allow for daylight saving time automatically' and let Windows handle the time change settings. In our support experience users who had the most trouble with 'time change' were those who either had a machine somehow get set to the wrong time zone or had tinkered with the default Windows settings.

3) Change the Directory Toolkit "Time Check Precision" setting (Options-Compare) from the default of 3 second to a value covering the new time differences between the two machines. For example, assuming the file content (and hence file size) has not changed, a value of 3600 would cause Directory Toolkit to report the files as the same even though their time stamp is one hour apart. The risks of this method are that "Time Check Precision" is a +/- range and not a specific value. Files 3 min, 15 min, 45 min would also be reported as the same. You may not want this...

4) Turn on the Directory Toolkit Binary Comparison mode, which will now report the files as the same.

5a) Use the Directory Toolkit "Add To File Time" setting in the Touch dialog to quickly touch the files on one or the other path. This field adds (or subtracts) the number of seconds you specify from the current file time. For example, to add one hour to the current file time, enter a value of 3600.

5b) Use our freeware FS Touch utility to handle the above 'touch' operation.

6) As a last resort our freeware TZAdjust utility may be helpful, if only to show the Time Zone and compensation values for the machines involved. Caveat: We strongly suggest leaving Windows 10 to the default settings.
 


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