NVIDIA based graphic cards which support AGP 8x mode (Accelerated Graphics Port) follow the AGP 3.0 specification.  The AGP 3.0 specification retains backwards compatibility with older AGP 4x technology.  All NVIDIA Geforce and Quadro GPU's which support AGP 8x mode are downwards compatible with AGP 4x motherboards.  When a graphics card which operates at AGP 8x mode is installed on a motherboard which only supports up to AGP 4x mode, the card will automatically switch to AGP 4x operation.