If you want a letter that doesn’t change every time you plug in your external drive, you may need to assign one. To change or assign a drive letter in Windows, start by plugging in the drive.
Go to Disk Management
Go to Control Panel / Administrative Tools / Computer Management / Disk Management
Wait for it to load. You will see a screen similar to this one.
Highlight the drive you want to change. Right-click on it and choose Change Drive Letter and Paths…
Change Drive Letter and Paths for …
Highlight the drive and click Change.
Change Drive Letter or Path
Choose a different letter and click OK.
Drive-letters A and B are reserved for floppy disk drives and, although historically irrelevant now, your drive will still be labeled that way. To avoid that, choose another letter.
Some letters are missing from this list because they’re already assigned on my computer; C to the hard-drive, D to the DVD-writer, and so on with other drives. Your mileage will vary.
Disk Management Warning
This warning message can probably be ignored. I’ve never had a problem. To be on the safe side, change the letter before adding files to the drive.