My girlfriend has an external hard drive with a bunch of photos on it from her Mac. She needed to transfer the files to her PC but we soon discovered that Macs and PCs use different formatting standards for hard drives. Initially, after plugging in the external hard drive to the PC, I ran diskmgmt.msc to make sure the computer was seeing it (since it wasn't showing up under My Computer), and indeed it did - but Windows prompted me to specify which type of file system it was. I don't remember exactly what the two options it presented were but I chose whatever the default option was. I believe it started with a G. It was only later that I learned I'd have to use third-party software to do it.

Now I'm worried that by simply telling Windows to choose one of those two file systems, it may have actually made some real changes to the disk's partition scheme, rendering it a brick. Because now when we go back to plug the drive into the Mac, this message pops up:

The disk you inserted is not readable by this computer.

Is it possible that Window's disk manager actually changed the partitions when I told it to expect a certain type of file system? Is there any way I can get this drive working on a Mac again?

2 Answers 2


Windows prompted me to specify which type of file system it was...

Windows disk management console doesn't ask you to tell it what type of file system it, it asks you what file system you want to write to it.

Is there any way I can get this drive working on a Mac again?

  1. Don't attempt to write anything to the disk
  2. Duplicate the drive to an image on her Mac (it doesn't matter if it's readable or not) using the following command where X is the drive identifier of your source (corrupted) drive.

      $sudo dd if=/dev/rdiskX of=~/Desktop/USB_Drive.img bs=1m
  3. Using a tool like Disk Drill or Disk Warrior, see if data can be recovered. It's free to diagnose, but you'll have to purchase a license to actually recover the data.

You don't have to make an image - that step is optional. However, if you attempt to make changes and it fails, you still have the original from which to make another image and try again.

  • Thank you so much! I will give this a shot. I'm copying the disk image right now, which will take some time. By the way, it has to be bs=1m with a lowercase "m" otherwise the commands gives an error.
    – soapergem
    Feb 17, 2019 at 0:37
  • @GordonMyers - Sorry for the typo....fixed!
    – Allan
    Feb 17, 2019 at 0:43

Windows cannot read HFS+. You need to either get third party drivers (like Paragon HFS+) for it or use a Mac. If you did format your disk, your data is gone. There's no such thing as telling Windows to expect a filesystem; you probably formatted it. If you only assigned a letter to it, the data should still be intact.

  • Generally agree with your answer, but formatting a disk doesn’t necessarily mean the data is gone. In many cases it just means the data is still there but the computer has no record of it. In such cases the data can be recovered using 3rd party software for data recovery or for rebuilding the drive’s directory.
    – Monomeeth
    Feb 16, 2019 at 23:38
  • “In many cases”... same chance as heads or tails....
    – Solar Mike
    Feb 17, 2019 at 4:44

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .