Points to Consider When Adding Drivers
Keep the following points in mind when designing a kernel-mode driver:
The system-supplied SCSI and video port drivers cannot be replaced.
A replacement lowest-level driver must implement the same functionality as the driver it replaces. For example, a replacement keyboard or mouse port driver must use the system-defined interface between itself and a system-supplied class driver that it reuses, and vice versa.
A new intermediate driver, inserted between any pair of system-supplied drivers, must interoperate with those drivers so that the functionality of the upper and lower drivers is not reduced.