What doesn't my motherboard work?

The official implementations of Quad SLI work in the same fashion. Two GPUs are placed on two separate PCBs, with their own power circuitry and memory. Both PCBs have slim coolers, cooling the GPU and memory. The 'primary' GPU can be considered to be the one on the rear PCB, or 'top' PCB (being on top when in a standard ATX system). The primary PCB has a physical PCIe x16 connector, and the other has a round gap in it to provide cooling for the primary HSF. Both PCBs are connected to each other by two physical links; one for 16 PCIe lanes, and one for the 400MHz SLI bridge. An onboard PCIe bridge chip, with 48 lanes in total, acts as the MCP does in SLI motherboards, connecting to both GPUs and the physical PCIe slot, removing the need for the motherboard to support SLI. One or both PCBs features an SLI connector, depending on the model.