Int 21 Fn 4404  - Dos 2+ - Ioctl - Read From Block Device Control Channel  [D]

   AX = 4404h
   BL = drive number (00h = default, 01h = A:, etc.)
   CX = number of bytes to read
   DS:DX -> buffer

Return: CF clear if successful
       AX = number of bytes actually read
   CF set on error
       AX = error code (01h,05h,06h,0Dh) (see #1366 at AH=59h/BX=0000h)

Notes: format of data is driver-specific
   this function was not supported by Digital Research's DOS-Plus

See Also: AX=4402h"DOS 2+",AX=4405h"DOS",INT 2F/AX=122Bh