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Daylight Savings, Standard Time & Reported File Times


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".

Assuming you are running an XP or above machine, this behavior is because:

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

2. 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.

3. One of the paths being compared is FAT32 and uses outdated driver software (e.g. a very old CDROM drive or USB drive).

This behavior is NOT a bug in Directory Toolkit!!! The sudden & puzzling difference in reported file times happens because the Windows operating system (XP and above) automatically adjusts the file time returned for a file based on "Universal Coordinated Time (UTC)" AND the Daylight Savings rules and Time Zone in effect for the computers involved. Assuming the paths being compared are on computers that are located in the same time zone, tf the operating system returns an incorrectly "adjusted" file time to Directory Toolkit, then Directory Toolkit displays file times that are different even though the two paths were previously identical.

This behavior can be very puzzling. The table below, which was created when we still had a Windows 98 computer, 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 copied to a Windows 2000 machine (FAT32 partition), a Directory Toolkit comparison of the two paths was opened, and the computer dates were changed on the two computers as per the conditions below. The NT 2000 machine was configured to "Automatically Adjust for Daylight Savings". Directory Toolkit was not set to perform "Binary File Comparisons" and no adjustments were made to the default "Time Check Precision" setting under Directory Toolkit's Options-Compare (see below).

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. Windows 98 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. It is also interesting to note that the MS-DOS time stamp under Windows 2000 does not change even though the OS reports a different time to Explorer and Directory Toolkit.

A search of the Microsoft Knowledge Base (support.microsoft.com) using the keywords "Time Zone" or "Daylight Savings" will turn up a variety of articles on this general issue. A good overall description is: Time Stamp Changes with Daylight Savings (Article Q129574).

We point out that although the above article refers to NTFS, the above test shows that this also happens under Windows 2000 on a FAT32 partition.

There are several ways to deal with this.

1) Make sure all your machines are set to the correct time zone for their location.

2) Allow your computers to adjust themselves for daylight savings or not. Do not fiddle with the time zone rules for your computer. Or any of the computers in your network! Although the Windows behavior of adjusting the reported file times may be unnerving to purists, our experience is that problems arise are almost always traceable to the default Windows OS settings having been tinkered with OR a machine simply being set to the wrong time zone in Regional 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.

5) 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.

6) As a last resort you can use our freeware TZAdjust utility to adjust the Time Zone rules for your computer, including the compensation value to use. Caveat: It is best to leaving Windows to default settings.
 


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