Yeah, the top slot is fixed x16 connected to the CPU and the lower x16 is actually x4 electrical and connected to the PCH. On more sophisticated motherboards, both slots are often connected to the 16 lanes from the CPU with switches that automatically reconfigure to an x8/x8 config when 2 cards are fitted (or even x0/x16 when just the lower slot used).Aurum wrote:rxh202, So if you moved a single 1080 to different slots then does the second 16x slot (PCI_E4) run at x4 when used alone??? I see from the photo that MSI labels the first 16x slot (PCI_E2) as PCI-E3.0 but no label on PCI_E4 just a different lock style.
In linux, the driver helpfully reports the PCIE link info (width 1x, 4x etc. and speed (that dynamically changes to save power, but was at 5 GT/s for Gen2 and 8 GT/s for Gen3 during tests)) for each connected card, so I've been able to confirm the speeds when running the tests.
Yep, that about sums it up! This experimentation has been informative for me, because in future I'll look for motherboards that allow both GPUs to be connected to the CPU (in an x8/x8 config).foldy wrote:So on Linux with a GTX 1080 gen3 x16 vs gen 3 x1 you loose only 4% and another 4% when going down to gen 2 x1.
But on your particular mainboard you loose another 10% when using mb instead of CPU connection.