Int 21 Fn 440D  - Ms-dos 7.0 - Generic Ioctl - Unlock Physical Volume      [D]

   AX = 440Dh
   CX = 086Bh (category code 08h, minor code 6Bh)
   BL = physical drive number (00h-7Fh = floppy, 80h-FFh = hard disk)

Return: CF set on error
       AX = error code (01h,02h,etc.) (see #1366 at AH=59h/BX=0000h)
   CF clear if successful

See Also: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Bh,AX=440Dh/CX=086Ah