How to restore the system/boot drive letter in Windows

Warning Do not use the procedure that is described in this article to change a drive on a computer where the drive letter has not changed. If you do so, you may not be able to start your operating system. Follow the procedure that is described in this article only to recover from a drive letter change, not to change an existing computer drive to something else. Back up your registry keys before you make this change.

For more information, click the following article number to view the article in the Microsoft Knowledge Base: This article describes how to change the system or boot drive letter in Windows. For the most part, this is not recommended, especially if the drive letter is the same as when Windows was installed. The only time that you may want to do this is when the drive letters get changed without any user intervention. This may happen when you break a mirror volume or there is a drive configuration change. This should be a rare occurrence and you should change the drive letters back to match the initial installation.

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.

This procedure swaps drive letters for drives C and D. If you do not need to swap drive letters, simply name the \DosDevice\letter: value to any new drive letter not in use.

Change the System/Boot Drive Letter

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

1. Make a full system backup of the computer and system state.
2. Log on as an Administrator.
3. Start Regedt32.exe.
4. Go to the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
5. Click MountedDevices.
6. On the Security menu, click Permissions.
7. Verify that Administrators have full control. Change this back when you are finished with these steps.
8. Quit Regedt32.exe, and then start Regedit.exe.
9. Locate the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
10. Find the drive letter you want to change to (new). Look for "\DosDevices\C:".
11. Right-click \DosDevices\C:, and then click Rename.
    
    Note You must use Regedit instead of Regedt32 to rename this registry key.
12. Rename it to an unused drive letter "\DosDevices\Z:".
    
    This frees up drive letter C.
13. Find the drive letter you want changed. Look for "\DosDevices\D:".
14. Right-click \DosDevices\D:, and then click Rename.
15. Rename it to the appropriate (new) drive letter "\DosDevices\C:".
16. Click the value for \DosDevices\Z:, click Rename, and then name it back to "\DosDevices\D:".
17. Quit Regedit, and then start Regedt32.
18. Change the permissions back to the previous setting for Administrators (this should probably be Read Only).
19. Restart the computer.