AMD today launched its first desktop Ryzen "Raven Ridge" APUs that combine quad-core "Zen" CPUs with "Vega" based integrated graphics solutions. One of its key specifications that caught our eye is its PCI-Express interface. Apparently, these chips feature just 8 PCI-Express gen 3.0 lanes for discrete graphics, besides 4 lanes dedicated as the chipset-bus, and 4 other lanes driving a 32 Gbps M.2 NVMe slot. What this means for the end-users, is that any discrete graphics cards plugged into the PCI-Express 3.0 x16 slot will run at half the bandwidth - PCI-Express 3.0 x8.

Our various PCI-Express scaling articles, which we regularly redo with the latest high-end GPUs, should tell you that the performance loss between gen 3.0 x16 and gen 3.0 x8 is negligible. This, however, becomes a problem for the small minority of users who combine these processors with AMD X370 chipset motherboards. The second x16 slot (which draws its PCIe lanes by segmenting it from the first x16 slot) won't work, and without at least x8 bandwidth, there's no possibility of NVIDIA SLI functioning, even on X370 motherboards that have SLI certification.