GeForce GTX Titan Two-Way SLI Scaling: PCIe 2 vs. PCIe 3
 

Back when I had Origin’s tri-Titan equipped Genesis in house, I received a few requests for benchmarks with PCIe 3 enabled. Because we tested the system with its default out of the box settings, the system was configured by default to only use PCIe 2 since NVIDIA does not officially support PCIe 3 on SNB-E based systems. As a result there was some interest in whether PCIe 3 would improve performance at all compared to PCIe 2, due to the high amount of PCIe bus traffic generated by three GTX Titan cards working together. IVB/Haswell is of course limited to 16 PCIe 3 lanes, whereas if PCIe 3 is enabled SNB-E systems have more than twice that with a combined total of 40 lanes, giving SNB-E a large bandwidth advantage.

As it turned out, the Intel DX79SR used in the Genesis supported PCIe 3, but only on the 2 full-fledged x16 slots. The third x16 slot (electrically x8) won’t operate beyond PCIe 2 speeds even after forcing it in NVIDIA’s drivers, which is unfortunately a bit of a double whammy since it’s the slot that’s already lacking in bandwidth. That dashed our hopes of a PCIe 3 vs. PCIe 2 comparison for tri-SLI Titans, and as a result the subject never reached print.

However in the last couple of weeks I’ve received several requests for two-way SLI Titan/780 PCIe performance benchmarks, which we did happen to collect while looking into tri-SLI and merely never published. So with that in mind we’re going to finally publish that data, since there’s clearly more interest in the matter than I initially expected.

http://www.anandtech.com/show/7089/g...ie-2-vs-pcie-3