Int 21 Fn 4404  U - Doubletools V1.0 - Get ???                             [k]

   AX = 4404h
   BL = drive number (00h = default, 01h = A:, etc)
   CX = 0006h
   DS:DX -> DoubleTools structure (see #1221)

Return: CF clear if IOCTL successful -- check DSPACKET for actual status
       AX = number of bytes actually transferred
   CF set on error
       AX = error code (01h,05h,06h,0Dh) (see #1366 at AH=59h/BX=0000h)

Note:  the Transporter device driver has the signature 55h 61h 50h 74h
     ("DaPt") twelve bytes after it beginning

Format of DoubleTools structure:
Offset Size    Description (Table 1221)
 00h   WORD    (call) signature 55h AAh
       (ret) signature 78h 70h ("xp")
 02h   WORD    (call) signature 52h 16h
       (ret) ???
 04h   WORD    (ret) segment of driver's DS (same as its PSP)