GPU Model # {: .center-image width:600px} It explains several important designs that recent GPUs have adopted. MMIO. The CPU communicates with the GPU via MMIO. Hardware engines for DMA are supported for transferring large amounts of data, however, commands should be written via MMIO. The I/O ports can be used to indirectly access the MMIO regions, but rarely used. An open source device driver Nouveau currently never uses it.
