How can I recover a Mac-formatted external hard drive? 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?
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?



Don't attempt to write anything to the disk
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

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.