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I'm currently choosing parts for a new computer, with my main focus on high PCI Express speed and a large number of slots. In this iteration, I will probably choose a board with an Intel Z97 chipset. The specification says that the Z97 chipset provides a total of 16 lanes Gen3 in 16 lanes, 8/8, or 8/4/4 configurations and 8 lanes Gen2. The mainboard, however, boasts with 4 PCIe slots, configurable with 16/16, 16/8/8 and 8/8/8/8 Gen 3 lanes. I suspect that these four ports are theoretically electrically capable of Gen3 but some of them will just use Gen2. But how can it provide more lanes than the chipset actually supports? Do boards have some kind of PCIe switch that distributes the available bandwidth on the lanes as-needed, capping the total bandwidth to that of 16 lanes, instead of 32, when in high load conditions?
Now I see, the CPU I had in mind has indeed 16 Gen3 lanes, so 8/8/8/8 with full Gen3 might just work. Thank you very much. – Jan – 2014-11-10T09:23:39.083
3IIRC some of those switches also allow card-to-card PCI-e connections. This is relevant because a common setup is to have two GPU's connected via PCI-e. (NVidia SLI, AMD XDMA). In such cases, bandwidth to the CPU is less of a constraint. – MSalters – 2014-11-10T14:13:58.463
Good point. Added to the post. – Hennes – 2014-11-10T14:17:29.687