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Does AMD's B550 support PCIe Gen 3.0 and Gen 4.0 simultaneously?

Pete wants to know if AMD's B550 chipset supports running PCIe Gen 3.0 and an PCIe Gen 4.0 simultaneously.

Question by Pete from United Kingdom (Great Britain) | Answered by in Storage on Sun, Oct 25 2020 8:19 PM CDT

Hi, I have a B550 motherboard (GIGABYTE B550i) and a GIGABYTE RX 5700 XT graphics card inside a custom case using a 30cm PCI-e riser cable.

The PCI-e riser cable is only gen 3.0, so I have had to set the PCIe graphics to "Gen 3.0" in BIOS (to overcome issues). My question is, can I upgrade to a PCI-e 4.0 SSD (e.g., Samsung 980 Pro) and use the SSD at PCI-e Gen 4.0 while keeping the graphics at Gen 3.0, or do I need to upgrade the riser cable to PCI-e 4.0 as well?

In other words, can the B550 chipset support graphics at PCI-e Gen 3.0 and an SSD at PCI-e Gen 4.0 at the same time? Thanks!

Hi Pete,

Definitely an interesting problem you have, so much that I had to test your scenario myself! That said, my test system motherboard is an X570 chipset Crosshair VIII Hero, so I'm not sure if you would see the same results on your B550i.

Does AMD's B550 support PCIe Gen 3.0 and Gen 4.0 simultaneously? 1 | TweakTown.com
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All of that said, on my x570 motherboard, I can make my top x16 slot Gen3 and keep PCIe Gen 4.0 working on both of my m.2 slots with my Samsung 980 Pro, with no issues. Looking at your motherboard specifications, it seems like you have the front m.2 slot under the heat sink that supports PCIe 4.0 from the CPU, so it will depend on your motherboard BIOS and the circuitry of the motherboard.

I can say not all B550 motherboards have CPU lanes dedicated to the m.2, so your board is quite good. Another thing to note here is, even if your setup doesn't allow PCIe 4.0 on the m.2 with the GPU at Gen3, the Samsung 980 Pro only loses 8-10 MB/s running in PCIe 3.0 mode 4KQ1.

Last updated: Nov 14, 2020 at 10:51 pm CST

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