PCIE Lanes with M.2/U.2 on ITX?

Random Guy Esq. · 13 Dec 2015 at 14:26

Howdy! Potentially daft question...

Does the use of an M.2 or U.2 SSD on an ITX motherboard cause the GPU to run at 8x rather than 16x? Or do boards have four separate PCIE lanes for high speed storage so that they don't use any of the GPU's bandwidth?

ExRayTed · 13 Dec 2015 at 16:04

Depends on the motherboard / cpu combo. If it's a standard 1150 / 1151 setup with only 16 PCI lanes then yes, it'll likely force the GPU down to X8

D1craig · 13 Dec 2015 at 17:00

Does this stand for the newer Z170 boards aswell? I know it's not a noticeable difference in performance but still would sate my appetite to know.

Random Guy Esq. · 13 Dec 2015 at 19:29

That's food for thought. I suppose it's only a very few FPS in the difference.

Meaker · 13 Dec 2015 at 21:16

You get 16x gen3 from the CPU and 4x gen3 from the chipset in z170 (shared in up to 20 lanes).

So any M.2 drives hooked into the chipset will not impact the link to the GPU, the only drawback is all devices on the chipset cannot exceed a combined 3.5-3.7GB/sec (the 4x gen 3 real bandwidth).

D1craig · 13 Dec 2015 at 21:18

Meaker said:
You get 16x gen3 from the CPU and 4x gen3 from the chipset in z170 (shared in up to 20 lanes).

So any M.2 drives hooked into the chipset will not impact the link to the GPU, the only drawback is all devices on the chipset cannot exceed a combined 3.5-3.7GB/sec (the 4x gen 3 real bandwidth).

so if both the gpu and the ssd can run upto 3.5/3.7 GB/sec then they will only run at half or atleast be restricted a bit anyway?

powelly · 14 Dec 2015 at 09:38

D1craig said:
so if both the gpu and the ssd can run upto 3.5/3.7 GB/sec then they will only run at half or atleast be restricted a bit anyway?

I think what he's saying as that the m.2/u.2 is running separately off the chip set whilst your pci-e slots are running from the cpu. Meaning you can run 8x/8x and the a separate 4x for the m.2/u.2 without them taking each others bandwidth.

Also the PCH supports an extra 20 pci-e lanes making a total of 36 lanes, meaning you could run multiple gpus and pci-e storage without an issue. On Z170 anyway

b0rn2sk8 · 14 Dec 2015 at 19:46

powelly2010 said:
I think what he's saying as that the m.2/u.2 is running separately off the chip set whilst your pci-e slots are running from the cpu. Meaning you can run 8x/8x and the a separate 4x for the m.2/u.2 without them taking each others bandwidth.

Also the PCH supports an extra 20 pci-e lanes making a total of 36 lanes, meaning you could run multiple gpus and pci-e storage without an issue. On Z170 anyway

Not all of those lanes are Gen3.

While everything posted above is technically correct it fails to take into account the other things that are connected to the chip that are already using the extra 4 lanes such as network cards, extra SATA ports, SATA express extra USB3/3.1, 2nd M.2 slot and a multitude of other hardware.

Each manufacturer sets up their board differently and even different boards from the same manufacturer will be different. You need to check each one, its no good saying there is 20 lanes so it must work at x16.

Also there is next to no difference between running a GPU at x16 and x8 even when running 3 way SLI. So the answer is don't worry about it.

See this Linus video: https://www.youtube.com/watch?v=rctaLgK5stA