A host microprocessor 40 communicates with a 3D graphics processing platform 41 to form a 3D graphics enabled computer system, with the host microprocessor 40 acting as a master device and the processing platform 41 acting as a slave device. The host processor recognises a 3D graphics API call from an application program 42 running on or communicating with the host processor 40 and communicates the API call to the processing platform 41. On receiving the 3D graphics API call from the host processor 40, the processing platform 41 carries out a 3D graphics processing operation in response thereto 47, e.g. generating data representing graphics primitives, rasterising the generated graphics primitives and rendering the rasterised graphics primitives.