What is the Architecture behind DirectX?

DirectX uses two drivers, the hardware abstraction layer (HAL) and the Reference Device/Reference Rasterizer (REF), to send requests to the hardware device. When DirectX is initialized, it checks the hardware to see if the hardware supports certain capabilities. If the hardware does support a certain capability, then the HAL will be used to access that hardware function; otherwise, the REF will be used to emulate the capability through software. The HAL directly uses the hardware functionality for output while the REF bypasses the hardware and implements its own functionality. Hence HAL will be much faster than REF. This architecture allows for easier expandability in future hardware.

You maybe in need of the REF when your HAL is producing some weird results. Suppose you're sure your code is correct, but the result is not what you're expecting. The REF device is guaranteed to behave correctly, so you may wish to test your app on the REF device and see if the behavior is the same. If it does works in REF then there are 2 chances

1. The graphics card is not supporting a feature that you assumed it does!
2. A driver bug. (You can contact the driver manufacturer or Microsoft if you are dead sure :) else if it doesn't work with the REF device then it's an application bug. (In most cases it won't be a REF bug. The Direct3D team implemented the REF rasterizer in a very straightforward way that isn't prone to bugs. Although it is slow it is solid too).

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