Windows NT operating systems, which includes all Windows versions this century (except WinME), will by default remember the drive letter that it has assigned to a partition or device and will always try to attach that same letter. It is not always successful with devices or drives that come and go, but for internal and fixed devices once a letter has been set it should persist. By using the Disk Management tool inside a Windows install we can add, remove or change drive letters and so permanently fix how that operating system sees and labels each drive or device.

What you can't do. You won’t be allowed in Disk Management to change Window’s own drive letter and this is indeed something you should not attempt by any means. You may also have another drive with a letter you can't change or remove and this may be a Windows System partition. In pre-Win7 versions of Disk Management it took a workaround to alter a System partition drive letter, but from Win-7 it is possible unless some important component such as a paging file has been placed on the drive.

Dependencies. On well used Windows systems or factory configured machines it would be prudent to be cautious in changing a drive letter because Windows or a software application may have a dependency to some component that will no longer be available if the path to its drive has been removed. Returning a letter to what it was is likely to restore any required links, but we would still advise that removing or changing drive letters is something that is best only done during the early stages of configuring a new system.

Remove a Drive letter

In this example (fig:1) we are going to remove the drive letter from the first partition so that it is no longer permanently visible to the Windows install that we are booted into, which is the C: drive on the second partition. Click or right click on the target partition and it will become partially shaded to indicate that it is the one in focus. The right click will also open a popup menu where we select the option Change Drive Letter and Paths….. which will take us to the next options box shown in fig:2.

Change a Drive letter

This is the options box we will receive (fig:5) if at the choices we were given in fig:2 we clicked the Change button. The little dropdown box when opened will display the list of available letters we can choose from. Select the one you want and click OK to bring up a warning notice similar to those we have already seen.

Changing a drive letter can have the same consequences for software components as removing one, so proceed with the same caution. If we don’t receive any further notices like those in fig:4, then clicking Yes will complete the letter change. If the letter we wanted for a drive or partition was already assigned to something else and so did not appear in the list of available letters in the drop-down box, then if possible we could first free up that letter by changing or removing it from the device that held it.

With Vista and Win7/8 a newly connected, created or changed drive will be quickly detected and this will automatically trigger the Autoplay function. In the case of a changed or added drive letter this will most likely bring up the Autoplay options box shown in fig:7, which you can just close, or deal with as you normally would.

Add a Drive letter

To add a letter to a partition or drive that currently has no letter attached to it then proceed as before to the step shown in fig:2. This time the list window will in typical circumstances be empty and the Add button will be the only available choice. Clicking it will give you the familiar options dialog where you can select a letter from the drop-down box. Once selected and you’ve clicked the OK button the operation will be immediately performed.

Mount in a Folder.
When you are adding a drive letter there will also be the option to mount to a folder, but we do not recommend this for multiboot machines or where you are cloning or moving operating systems around. We advocate keeping things as simple as possible as it can be easy to lose track and control of volumes and data if they are not all kept in the one place with distinct and fixed labels. For experts only. See here for a little bit more and some links.

No Drive Letter.
Remember that Disk Management will only work with partitions that are fully Windows supported. If a partition is of a non-Windows file system, or has been modified in certain ways perhaps by backup software or a manufacturer’s recovery system, or it has been hidden by a bootmanager, then it won’t be possible to give it a drive letter.

When a drive letter leads to the wrong device.

If you have various USB drives and devices and maybe other drives and partitions and even network drives that all come and go and share the same drive letters, then sometimes Windows can get a little confused and show a drive letter as being attached to one device when it actually leads to another. On some occasions no amount of plugging a device in and out will cure the problem and you can be left totally unable to access a device. One solution is to use Disk Management to remove the attached drive letter from a device and then give it a new letter you don’t think your system has used before. Another way for the more experienced is to manually trim the list of previously mounted devices in the Windows registry. Tidy out the registry's /MountedDevices key.

Changing Windows own drive letter.
Certain ways of installing Windows can result in the operating system seeing itself as something other than the default C: drive. If you have a desire to change the letter of an existing Windows install then bare in mind that the drive letter is defined and imprinted at conception and it becomes so ingrained that by the birth and first boot-up of a new install it has become so intertwined throughout Windows that it would take Herculean efforts to change. We advise that it is not worth the effort trying and a full reinstall of Windows, even if that was going to take days, would probably be quicker and have the advantage of being a clean system you knew didn't have some hidden instability that was just waiting to surface and bite you. The best way to determine and set a Windows drive letter is at install time.Managing the install of Windows to determine a few variables.

Recovering from an accidentally changed Windows Drive Letter.
When cloning, moving or deploying a Windows install it can happen that on first bootup after a move the Windows OS will have changed its own drive letter, which will result in an unusable and an all but destroyed operating system. Fortunately it is not too difficult in Vista and 7 to restore the original drive letter. Restoring an Original Windows Drive Letter.

How drive letters are maintained.
If you want to know a bit more about how drive letters are allocated and maintained; where they are stored in the Windows registry; and what their connection is to a drive's Disk Signature; then have a look at our Tech-Insight article on the subject. The Disk Signature and Windows Drive Letters