What is Nvidia Hybrid SLI?
I found a very good information from Hothardware.com : NVIDIA’s Hybrid SLI technology gives users the ability to pair an IGP, or mGPU (motherboard GPU), with a discreet graphics card, or cards, for two new modes of operation. NVIDIA calls these new modes Hybrid Power and GeForce Boost. GeForce Boost does what its name suggests. By coupling the motherboard’s integrated GPU with a discreet graphics card, the 3D rendering workload is shared between the two GPUs for a boost in performance. Currently, GeForce Boost is only supported by GeForce 8400 GS and 8500 GT discreet cards, as for the IGP, only the next-gen nForce 700a series of chipsets due to arrive this quarter will be supported initially.