Windows uses MountMgr to manage and support the system volume information, a very important file and at the same time, a driver that can be found in C:\Windows\System32\drivers and it’s named MountMgr.sys.

It allocates, reallocates and removes drive letters for all devices. Most of the times, you can manage this by going to Start – Run and typing there “compmgmt.msc” without the quotes, then press Enter.

Change drive letter assignments - Computer Management

This is where you will see a disk management window, where you can also change the letter of any plugged in device after you see it displayed in here. If you don’t see it in Disk Management, there might be another problem with your plugged in device like for example incorrect or missing driver, broken device and others. If it won’t be displayed in here, try to troubleshoot the problem by going to device manager and see if you can find it in there.

If you find it in there, you might also see some additional sign, like a yellow exclamation mark or a yellow question mark, meaning that the driver is incorrect or missing. If you don’t see it, try to test it on another computer, maybe it is broken or the type of device is disabled from BIOS. There are of course, other possible causes for such a device not being displayed in Disk Management, but I will stop here and hope that you can find them out by yourself. If you don’t, you can always ask me via a comment or the Questions and Answers section and I will do my best to answer you in a few hours tops.

Sometimes, when you will plug in devices to your computer, they won’t be displayed in My Computer, along with the rest of your drives and assigned letters in there. Those are the times when you must consider the fact that Windows failed you again and the MountMgr wants to assign a letter to the drive, usually the next free drive letter after all those taken. For some reason, it would assign a letter you already have assigned to a network folder (net use feature), to a SUBSTed folder or another device that just has taken the same letter that MountMgr wants to use for this new device.

You will have to find this device in Disk Management, right click it and use “Change Drive Letter and Paths..”.

Change drive letter assignments - Change driver letter and Paths

After this, just pick another letter, something different than A, B, C, D, E (usually used by Floppy Drives, Windows Partitions or CD and DVD Drives) and those you already see displayed in My Computer and Disk Management by selecting the current assigned letter, in my case F, and selecting the “Change” button.

Change drive letter assignments - Change letter

Change drive letter assignments - Assign letter

Once you selected another drive letter to be the NEW drive letter of the device plugged in, the OK button will be activated and you can click it to confirm the process.

By this time, you will get the last confirmation dialog box, which is actually a warning about the programs that you are running and use this letter. Most of them will just refresh, for the rest, you have to restart them. Just confirm with a Yes, with no worries.

Change drive letter assignments - Allow accesss

Most common problem that will force you to change the drive letter of some device will be the use of a new device that you just plugged in and you can see it in Disk Management but not in My Computer, as an accessible drive.

The change of a drive letter in Windows is not needed only when you got a device plugged in and you can’t see it in Windows Explorer. As you found out already, you will also use this according to your preferences.

I will also mention that there are multiple ways to access the same management window from Windows Vista, Windows XP and Windows 7, but the one I presented is a common one and it is located and accessible for all versions in the same way. Else, you could find it in Start – (Settings – depends on the Start menu type ) Control Panel – Administrative Tools – Computer Management – Disk Management.

To remove or add a drive or a drive letter just follow the steps in the same window, as you can see in below picture and according to your needs, ADD to add a new Drive letter or path and REMOVE to delete the assignment, even if the device will still be displayed in Disk Management.

Change drive letter assignments - Add/Remove

This is a simple procedure that can help you and get you out of some nasty situations with devices and sometimes even folders or network files and folders.

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