There is, to assign a specific letter to a removable drive first plug the drive in. Right click on the start button and select Computer Management. On the left side click Storage > Disk Management. On the right side right click on the external drive you want to assign the fixed mapping letter to and click Change Drive Letter and Path. In the dialog box click change, select (if not selected) the Assign the following drive letter and select the letter you want from the dropdown. Click OK.