REM ------------------------------------------------------------------------------- REM On System Drive, the files DRIVE-.? indicate letters not to be assigned REM ------------------------------------------------------------------------------- => FOR %%U IN (!TMP_OLD_LETTER!:\DRIVE-.?) DO ( SET TMP_NOT_FREE=%%~xU SET TMP_FREE_LETTER-!TMP_NOT_FREE:~1!= ) I can verify that is code does in fact fix the problem with free letters not be reserved.