The primary device type is the hardware device, which supports hardware-accelerated rasterization and both hardware and software vertex processing. If the computer on which your application is running is equipped with a display adapter that supports Microsoft Direct3D, your application should use it for 3-D operations. Direct3D hardware devices implement all or part of the transformation, lighting, and rasterizing modules in hardware.
Applications do not access 3-D cards directly. They call Direct3D functions and methods. Direct3D accesses the hardware through a hardware abstraction layer. If the computer running your application supports the abstraction layer, it will gain the best performance by using a hardware device.
Note: Hardware devices cannot render to 8-bit render target surfaces.
Direct3D supports an additional device type called a reference device or reference rasterizer. Unlike a software device, the reference rasterizer supports every Direct3D feature. Because these features are implemented for accuracy, rather than speed, and are implemented in software, the results are not very fast. The reference rasterizer does make use of special CPU instructions whenever it can, but it is not intended for retail applications. Use the reference rasterizer only for feature testing or demonstration purposes.