Int 2F Fn 1607  C - Ms Windows 3.1 - "blockdev" Virtual Hard Disk Device   [W]

   AX = 1607h
   BX = 0010h (VxD identifier of "BLOCKDEV")
   CX = function
       0001h starting FastDisk compatibility tests
       0002h ending FastDisk compatibility tests
       0003h check if FastDisk installation allowed

       Return: CX = 0000h if allowed

Note:  this interface is called by the Windows FastDisk driver (such as
     WDCTRL) when it thinks that the INT 13h handler immediately below
     IO.SYS's INT 13h code is not in ROM; it should be supported by any
     program which hooks itself underneath IO.SYS's INT 13h code with
     INT 2F/AH=13h

See Also: AX=1607h/BX=0014h,INT 2F/AH=13h