Whenever we connect a drive whether new or the earlier connected, Windows assign it a unique Drive Letter randomly. Managing these letters is possible in Windows through diskmgmt.msc but only for the connected drives.

Then what if your drive is not connected to the system? Also for those who want a specific drive letter to their specific drive always, this can be done using the tool called DriveLetterView.
DriveLetterView is a simple utility that allows you to view the list of all drive letter assignments in your system, including local drives, remote network drives, CD/DVD drives, and USB drives - even if they are not currently plugged. It also allows you to easily change a drive letter of USB devices and remote network shares, as well as to delete a drive letter of USB device that is not plugged.
The tool also allows you to save the list as a txt, csv, html or xml file. This utility works on every version of Windows, starting from Windows 2000 and up to Windows 7/2008. Both 32-bit and x64 systems are supported.
In order to change/remove drive letters on Windows 7/2008/Vista, you have to right-click on DriveLetterView.exe and choose ‘Run As Administrator‘. If you run it without admin rights, DriveLetterView can display the list of all drives, but you won’t be able to change/remove a drive letter.
Download DriveLetterView