User-mode display drivers
Along with a kerne-mode display driver, graphics hardware vendors must also write a user-mode display driver (UMD) for their display adapters. The UMD is a dynamic-link library (DLL) that the Direct3D runtime loads.
The UMD can consist of one DLL that supports multiple Direct3D versions, or it can consist of separate DLLs. The following articles discuss various aspects of the UMD:
Returning Error Codes Received from Runtime Functions
Handling the E_INVALIDARG Return Value
Converting the Direct3D Fixed-Function State
Supporting Multiple Processors
DirectX Video Acceleration 2.0
Supporting Direct3D Version 10
Supporting Direct3D Version 10.1
Supporting Direct3D Version 11
Processing High-Definition Video