Restore the system or boot drive letter in Windows

This article describes how to change the system or boot drive letter in Windows.

Original product version:   Windows 10 - all editions, Windows Server 2012 R2
Original KB number:   223188

Summary

Warning

Don't use the procedure that's described in this article to change a drive on a computer where the drive letter hasn't changed. If you do so, you may not be able to start your operating system. Follow the procedure that's 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.

This article describes how to change the system or boot drive letter. Usually it isn't recommended, especially if the drive letter is the same as when Windows was installed. The only time that you may want to do so is when the drive letters get changed without any user intervention. It may happen when you break a mirror volume or there's a drive configuration change. This situation 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 can't 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 don't need to swap drive letters, name the \DosDevice\letter: value to any new drive letter not in use.

Change the system or 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, see How to back up and restore the registry in Windows.

  1. Make a full system backup of the computer and system state.

  2. Sign in as an Administrator.

  3. Start Regedt32.exe.

  4. Locate the following registry key:

    HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices

  5. Select MountedDevices.

  6. On the Security menu, select Permissions.

  7. Verify that Administrators have full control. Change it 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 select Rename.

    Note

    You must use Regedit instead of Regedt32 to rename this registry key.

  12. Rename it to an unused drive letter \DosDevices\Z:.

    It frees up drive letter C.

  13. Find the drive letter you want changed. Look for \DosDevices\D:.

  14. Right-click \DosDevices\D:, and then select Rename.

  15. Rename it to the appropriate (new) drive letter \DosDevices\C:.

  16. Select the value for \DosDevices\Z:, select 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. It should probably be Read Only.

  19. Restart the computer.