Int 6F Fn 18  - 10net V3.3+ - Unmount                                      [N]

   AH = 18h
   AL = local drive number (0=A:)
   BL = type
       00h     disk
       01h-03h LPTn
       04h,05h COMx

Return:    CF clear if successful
   CF set on error
       AX = error code (see AH=00h)

See Also: AH=17h