Z390 and PCIe x16 slots

[martman]

Are there any top end mobos that have at least 2 PCIex16 slots for SLI? or is it still a thing that graphics cards still really don't need over 8x?

 

[mv2devnull]

Not with Z390. Z299-based board and a 44-lane CPU apparently can: https://www.asus.com/Motherboards/PRIME-X299-DELUXE/specifications/

Perhaps something with AMD Threadripper too.


For x16 vs x8 a websearch did pick up: https://www.gamersnexus.net/guides/3366-nvlink-benchmark-rtx-2080-ti-pcie-bandwidth-x16-vs-x8

 

[martman]

Thank you, interesting read.

 

[Topweasel]

The big key that Mv2 was getting at is that the consumer boards from AMD and Intel running their consumer CPU's (AM4 and 115x respectively) only have 16x PCIe lanes dedicated to GPU usage. Some Intel boards will say that something like PCIe 16x slot 3 is 16x as well but what it is doing is using the plx like functionality of the chipset to create more PCIe lanes but their communication back to the CPU is really at the PCIe 4x speeds from the 4 lanes the CPU connects to the chipset. AMD is the same way but any PCIe slots fed from the chipset are usually split (instead of multiplied) from the lanes fed from the CPU to the chipset. A Ryzen does have 4 extra lanes but those are used for a dedicated connection to the M.2 slots.

I would also like to note that the X299, you might have to be careful when selecting the boards. Since Intel supports 3 different lane configurations, some boards are very careful not to feed certain slots from the CPU and instead use the chipset (and therefore the same 4x connection as the Z370/390) for compatibility reasons. X399/X499 from AMD doesn't have this issue since all Threadrippers have 60 free PCIe lanes (because 4 is dedicated to the chipset).