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Time "shifting" when moving files using PC-formatted media

Time "shifting" when moving files using PC-formatted media

We've received a number of reports from a reader who, after extensive testing, has found that transferring files using PC-formatted removable storage -- such as a Zip disk or a "memory stick" -- between a Mac running OS X and a Windows computer running Windows XP results in an odd four-hour time shift in the files' modification dates. What's more, the same media, when used to transfer files between an OS 9 Mac and Windows XP, does not show this problem, nor does it have a problem transferring files between Macs when the media is formatted as a Mac volume. Below are a few examples of "experiments" that the user has tried:

Insert a PC-formatted memory stick in the USB port on Windows machine; create a file and save it to the memory stick. Move the memory stick to another Windows machine == modification dates on the document shows the correct time. Move that memory stick to a PowerBook G4 (12") running OS X 10.2.x == modification date is four hours behind the Windows machines.

With a PC-formatted disk in an iMac running OS 9, save files from iMac hard drive to Zip -- times show up correctly on the Zip disk at this time. Move that Zip disk to the PowerBook running OS X, and the times show up as four hours behind. But if you move that Zip disk back to the iMac running OS 9, the times are correct.

With a PC-formatted Zip disk, if you mount the Zip disk on the PowerBook (OS X), and then copy a document created on the PowerBook to the Zip disk, the modification date stays the same; if you copy a document created elsewhere (e.g., one created on a Windows machine and later transferred to the PowerBook), the document's modification date changes to the current time/date -- i.e., the file loses its original modification date. If you then move this Zip disk to the OS 9 iMac, the times on the files are all four hours ahead.

Note that the above problems only seem to occur when using PC-formatted media. The same experiments provide normal results -- no time differences -- when using a Mac-formatted Zip disk between the OS 9 iMac and OS X PowerBook. Problems also do not occur when burning a CD using the OS X Finder on the PowerBook, then taking that CD to a Windows machine (i.e., the times are the same). Of course, the OS X Finder burns hybrid Mac/Windows CDs by default.

We seem to remember hearing about a problem with time differences when copying files between Mac and Windows computers in this way; however, we haven't been able to dig up any more info.

Have you heard of such time-shift problems? Drop us a line at

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