Question Any boards with PCIe 4.0 in dual x16 mode (electrical lanes not physical)

May 8, 2021
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Hi,

I just purchased GIGABYTE X570 Aorus Ultra and I'm disappointed as for CrossFire mode PCIe works in x8 mode as lanes are split into 2 slots. So single GPU will work with x16 speed and 2 GPUs together will work in x8 mode each. Are there any motherboards supporting PCI 4.0 x16/x16 on both slots to not bottleneck both GPUs? I found some for Threadripper with PCI 3.0 -even in triple mode x16/x16/x16 but that is PCIe 3.0 not 4.0.

I'm going to put there two rx 6900xt (already bought). The reason for such powerful setup is monitor that I bought in autumn- Samsung Oddysey 9 with 5160x1440p and it is hard to get very good game performance here.

Thanks
Adrian
 

Zerk2012

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Hi,

I just purchased GIGABYTE X570 Aorus Ultra and I'm disappointed as for CrossFire mode PCIe works in x8 mode as lanes are split into 2 slots. So single GPU will work with x16 speed and 2 GPUs together will work in x8 mode each. Are there any motherboards supporting PCI 4.0 x16/x16 on both slots to not bottleneck both GPUs? I found some for Threadripper with PCI 3.0 -even in triple mode x16/x16/x16 but that is PCIe 3.0 not 4.0.

I'm going to put there two rx 6900xt (already bought). The reason for such powerful setup is monitor that I bought in autumn- Samsung Oddysey 9 with 5160x1440p and it is hard to get very good game performance here.

Thanks
Adrian
First we will start with some basics. PCI-E 4.0 X8 has the same bandwidth of PCI-E 3.0 X 16 (on paper) they could be a bit of performance difference in real world but not enough to matter.

Now for Xfire it's dead in 2021 in fact pretty much was dead a few years ago and developers stop putting support for it in most games the same as SLI. Their still a few games that can use it and show a bit of performance increase but their also games that will actually get less FPS than using a single card. Then you can get into skipped frames and a lot of other problems but I will just skip that part.

6900 XT 3.0 vs 4.0

View: https://www.youtube.com/watch?v=VKWi1XvWszk

EDIT here is a list from 2020 also read some of the comments below the list some games are disputed.
https://amdcrossfire.fandom.com/wiki/Crossfire_Game_Compatibility_List
 
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May 8, 2021
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Thanks @Zerk2012 , thanks @sizzling
And on any other socket, is there anything supporting 2x pcie x16? (with PCIe 4.0)

Based on that movie Zerk2012 (if that is true -I'm surprised that everywhere it is just 1 fps diff between PCI 3.0 and 4.0) it means data transfer is not a bottle-neck. And when I will connect cards on my board, both will run on x8 speed 4.0 what is exactly the same if I would have x16 on PCI 3.0 (https://en.wikipedia.org/wiki/PCI_Express). I also bought a used MSI board (still can return it back in 2 weeks after purchase) wherein crossfire works with x16 in 1st slot and x4 in 2nd slot under PCIe 4.0. I hope I will have some time for tests next week, if so I will share my own results from both setups.
 
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