After an excessively difficult time of upgrading a CD-ROM to a DVD RW, XP added insult to injury doing a number on me with drive letter assignments. A little background on the system – it is an older Dell Dimension that got a hard drive upgrade about 6 months ago. The original 30GB hard drive was imaged to a new drive – which included (ugh!) the Dell management partitions. The original 30GB drive was left in because the client wanted to be 100% sure all the data was imaged over to the new drive – which meant the original management partition was still there. So basically there are now four hard drive partitions, a and DVDRW, four mapped network drives (starting with G:) and they wanted to add a USB flash drive and external hard drive. Oh, and a floppy drive just for fun.

After the CD-ROM to DVDRW upgrade, XP decided to assign drive letters to the management partitions – F: and G:! SO now the first mapped network drive didn’t work and neither of the USB drives showed up in My Computer. Naturally, my first stop was the Disk Management console to change (or remove) the drive letters for the management partitions. Unfortunately, when I right clicked on either of the management partitions, my only option was “Help” – not helpful.  I knew there had to be another way to change drive letters without using the management console and found the solution in the registry with some help from the great folks at Petri IT Knowledgebase.

The steps below came from Daniel Petri and it should be made very clear that this procedure is not to be taken lightly and should be used as a last resort only.

To change or swap drive letters on volumes that cannot otherwise be changed using the Disk Management snap-in, use the following steps:

Note: In these steps, drive D refers to the (wrong) drive letter assigned to a volume, and drive C refers to the (new) drive letter you want to change to, or to assign to the volume.

  1. Make a full system backup of the computer and system state.
  2. Log on as an Administrator.
  3. Start Regedt32.exe (or Regedit.exe in Windows XP).
  4. Go to the following registry key:
  1. Click MountedDevices.
  2. On the Security menu, click Permissions.
  3. Check to make sure Administrators have full control. Change this back when you are finished with these steps. (I logged is as a member of the local admin group and had full control already)
  4. Quit Regedt32.exe, and then start Regedit.exe.
  5. Go to the following registry key:
  1. Find the drive letter you want to change to (new). Look for “DosDevicesC:”. (Typically at the bottom of a long list.)
  2. Right-click DosDevicesC:, and then click Rename. In Windows 2000 you must use Regedit instead of Regedt32 to rename this registry key.
  3. Rename it to an unused drive letter “DosDevicesZ:”. (This will free up drive letter C: to be used later.)
  4. Find the drive letter you want changed. Look for “DosDevicesD:”.
  5. Right-click DosDevicesD:, and then click Rename.
  6. Rename it to the appropriate (new) drive letter “DosDevicesC:”.
  7. Click the value for DosDevicesZ:, click Rename, and then name it back to “DosDevicesD:”.
  8. Quit Regedit, and then start Regedt32 (not required in Windows XP).
  9. Change the permissions back to the previous setting for Administrators (this should probably be Read Only).
  10. Restart the computer.

It worked perfectly for me, but again – back up the registry before you make any changes. That’s just “best practice” and should never be ignored. Here is the link to the original post as well as a few others: