INT 21 - DOS 2+ - IOCTL - WRITE TO BLOCK DEVICE CONTROL CHANNEL
        AX = 4405h
        BL = drive number (00h = default, 01h = A:, etc)
        CX = number of bytes to write
        DS:DX -> data to write
Return: CF clear if successful
            AX = number of bytes actually written
        CF set on error
            AX = error code (01h,05h,06h,0Dh) (see AH=59h)
Note:   format of data is driver-specific
SeeAlso: AX=4404h,INT 2F/AX=122Bh