Int 21 Fn 440E  - DOS 3.2+ - Ioctl - Get Logical Drive Map                 [D]

   AX = 440Eh
   BL = drive number (00h=default,01h=A:,etc)

Return: CF set on error
       AX = error code (01h,0Fh) (see AH=59h)
   CF clear if successful
       AL = 00h block device has only one logical drive assigned
        1..26 the last letter used to reference the drive (1=A:,etc)

Note:  DR-DOS 3.41-5.0 DRIVER.SYS does not support drive mapping and thus
     always returns AL=00h

See Also: AX=440Fh,INT 2F/AX=122Bh