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Pci-e lanes with ryzen


#1

So I’m building a new ryzen 2 system, and I noticed the ryzen only supports 20 open pci-e lanes. Will I be going over that with a 1080 and 2 nvme drives, or will I just be at the limit?


#2

Ryzen have direct M.2 to CPU connection. The 20 lanes are 16 for GPU and 4 for the chipset. If you can saturate the chipset lanes - then you may be in trouble…
But in general use, you should be fine.
Just make sure your board supports dual NVMe drives. Some boards support only one NVMe, that is directly wired to the CPU and the other M.2 slot is only SATA. So choose wisely.


#3

Isn’t it 20 CPU PCI-e Lanes and an addition 8 2.0 chipset lanes?

So it’d be 16 for GPU, 4 for NVMe, and 8 for w/e you want after that wouldn’t it?

So the 1080 would be using x16
NVMe_1 will be using M2_1 which is x4
NVMe_2 will be using M2_2 which should be the chipset lanes.


#4

8x 2.0 = 4x 3.0
(8x 2.0 is actually little bit faster than 4x 3.0)

// In some mobo’s you can edit the bios, and turn off more SATA ports and assign them to 2nd NVMe_2 port making it almost 8x 2.0.)

Internally ryzen has 32 pci-e lanes;
but only 24 are available.


#5

Here is the primary source:
https://www.amd.com/en/products/chipsets-am4

With your edit, now everything is right.
On some boards it should also be possible to run the 1080 on x8 and use the rest of the CPU lanes for the second NVMe drive.
Although the chipset lanes should be enough for the second NVMe drive. There are not many NVMe drives that really need that much bandwidth.


#6

So I checked my mobo which is an asrock x370 Fatal1ty Professional gaming.
Layout:

I can do…

So in your use case with this mobo
PCIE2 - 3.0 x16 - GTX_1080
M2_1 - 3.0 x4 - NVMe_1
M2_2 - 2.0 x4 - NVMe_2


#7

If you can set the GPU slot to just use x8 PCI-E as mentioned above, this shouldn’t be a problem regardless. What I’ve seen so far indicates a 1080 doesn’t saturate x8 PCI-E 3.0 so there shouldn’t be any noticeable performance hit.


#8

I’ll add that i’ve noticed approximately zero difference between PCIe 3.0 16x and 8x with Vega64 also.


#9

My long term goal for my new build is to install this card and use it as a boot drive. Should I just start eyeing a thread-ripper build instead?


#10

If you are thinking about using that, keep in mind that you need Bifurcation Support on your motherboard. (At least I am quite certain it is required, maybe one of the motherboard gurus can help out.)