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
Don't 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, see Unable to log on if the boot partition drive letter has changed.
This article describes how to change the system or boot drive letter. 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.
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, name the
\DosDevice\letter: value to any new drive letter not in use.
Change the system or boot drive letter
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.
Make a full system backup of the computer and system state.
Log on as an Administrator.
Go to the following registry key:
On the Security menu, click Permissions.
Verify that Administrators have full control. Change this back when you are finished with these steps.
Quit Regedt32.exe, and then start Regedit.exe.
Locate the following registry key:
Find the drive letter you want to change to (new). Look for
\DosDevices\C:, and then click Rename.
You must use Regedit instead of Regedt32 to rename this registry key.
Rename it to an unused drive letter
This frees up drive letter C.
Find the drive letter you want changed. Look for
\DosDevices\D:, and then click Rename.
Rename it to the appropriate (new) drive letter
Click the value for
\DosDevices\Z:, click Rename, and then name it back to
Quit Regedit, and then start Regedt32.
Change the permissions back to the previous setting for Administrators (this should probably be Read Only).
Restart the computer.