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Motherboards with PCI-E x4 Slot Above First x16 Slot

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post #1 of 1 (permalink) Old 05-18-2020, 12:45 PM - Thread Starter
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Motherboards with PCI-E x4 Slot Above First x16 Slot

I am in a bit of a weird situation perhaps. My PC is built into a Lian-Li DK-03X desk case. See attached photo. In this desk case, the PCI-Express cards are all set up vertically one above the other, with riser cables used to extend the motherboard's slots. The issue is that I have a sound card and a graphics card (and I definitely want to keep using both). Because of the physical arrangement, the riser cable from top slot ends up on the bottom when it comes to the PCI-Express cards. As you all know, most motherboards have the very first slot as a PCI-E x16 slot meant for the graphics card.

If I use the first two PCI-Express slots on my motherboard with riser cables and connect the graphics card to the top slot, then the graphics card is BELOW the sound card. To ensure my graphics card is ABOVE my sound card, I need to then use the first slot for my sound card and the second slot for my graphics card. This optimises the look (I watercool my graphics card) and the space for the tubing. Unfortunately this means my graphics card is always working at PCI-E x8. This is the case even if I use a PCI-E x4 slot for my sound card, at least on my current motherboard (Asus Maximus X Hero). The ironic bit of luck is that my current motherboard has a PCI-E x4 slot ABOVE the first PCI-E x16 slot on the motherboard, so the card layout is fine and the graphics card is working at PCI-E x16.

I'm thinking of upgrading to an AMD Ryzen 9 3950X build and the Asus Crosshair VIII Hero Wi-Fi is the motherboard I'd go for. However, this motherboard (or any I've seen for that matter) don't have any slots above the first PCI-E x16 slot. This means that if I want my graphics card ABOVE my sound card inside the case, I would need to accept a PCI-E x8 link, be it PCI-Express 3.0 (my current NVIDIA GeForce RTX 2080Ti) or 4.0 (upcoming NVIDIA GeForce RTX 3000 series cards, I believe).

Bit of an odd situation. Does anyone envisage loss of performance because of the PCI-E x8 link? Maybe not now with my 2080Ti on PCI-Express 3.0 but maybe with the upcoming 3000 series cards on PCI-Express 4.0? Or maybe the PCI-Express 4.0 bandwidth is high enough such that x8 link speed is still over the graphics card's requirements. I'd love it if I could use a PCI-E x4 slot half-way down the motherboard for my sound card and the PCI-E x16 slot below that for my graphics card, and my motherboard maintain the x16 link speed for the graphics card, but I think this is never the case, no? It just defaults to x8 link speed because you didn't use the first PCI-E x16 slot. Maybe a BIOS setting? I doubt it but worth asking.

Thank you in advance.
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