A Microsoft-provided class driver is an intermediate driver designed to provide a simple interface between a vendor-written miniport driver and the operating system. A miniport driver is a hardware-specific DLL that uses a Microsoft-provided class driver to accomplish most actions through function calls, and provides only device-specific controls.
Under WDM (Windows Driver Model), the miniport driver registers its associated hardware adapters with the class driver, and the class driver creates a file object to represent each port/miniport combination that registers. (The registration process is described in the reference section of the Microsoft DDK.) Each minidriver uses its paired class driver's device object to make support routines. The class driver is accessed by the outside world through WDM CSA.