I would be surprised if the PCIe Switches chips add any latency as they are acting, in this case, as a simple static switch rather than a multiplexer. In "SLI-Capable" boards based on X470 or Z370/Z390 the PCIe switches just take the upper 8 lanes from the top PCIe3 x16 slots and switch them to lower 8 lanes of the middle slot when the motherboard detects a card inserted there.HaloJones wrote:@Nathan_P, another machine (i5-2400, P67 mojo, 1070 at the same clock, Windows10) is getting 700K with these units so I'm just wondering if the relative slowness of this dual 1070 rig could be down to the alleged latency built into Z77 boards that use a PLX chip to achieve 2 slots at x16. I'd never read about this inherent latency until today. I had a simpler Z77 board with these two 1070s but it died when the PSU blew. I replaced it with this Gigabyte Sniper G1 board that promised 2x x16 but now it may be that this is at the cost of some latency on the PCIE channels. Hopefully when some Core22 units come back I can get a better picture of how much this improves the output.
In Higher-end boards the PLX switches actually multiplex the PCIe lanes to multiple slots and take care of arbitration etc. so these would add latency.
It is confusing as both are referred to as "Switches" whereas one is a switch and the other a multiplexer.