Which PCIe slot for GPU

Dear All

My motherboard has 3, full-length PCIe 3.0 slots labelled

PCIe 3.0 x 16 (the one nearest the CPU)
PCIe 3.0 x 4 (the 2nd one down)
PCIe 3.0 x 8 (the one furthest away from the CPU)

My GPU is a PCIe 2.0 x 16 card. Does it matter much which slot I use? ie what's the effect of using a Gen 2.0 x 16 card in a Gen 3.0 x16, x 4 or x 8 slot?

I know that I'm supposed to put the GPU in the x 16 slot nearest the CPU but for some reason, my PC won't POST reliably on first press of the power button when the GPU is in that slot. I've been trying to track down why this is for over two weeks now but so far zilch. The PC will POST 50% of the time but the rest of the time, I have to press the power button 3 times - once to power up (no POST), second to power down, third to power up. The behavior is consistent.

However, I don't see this if I move the GPU to one of the other slots but I'm worried I might be getting poor performance doing that.

Motherboard MSI Z170A Gaming 9 ACK
GPU Nvidia Quadro K4200

Thanks in advance

Use the top x16 slot. Then the rest for subsiquent cards or other items.

PCIe 2.0 x16 is basically the same as 3.0 x8, so I'd suggest the one furthest away from the CPU.
It'll work in the middle one tho, and based on the age of the card you probably won't saturate that slot's data capabilities.

Given the problem you face, I'd suggest looking for another motherboard though.

@GnomishViking : he said he can't use that slot because the PC fails to boot 50% of the time if there's a card in it.

Not exactly how it works. The card and slot would both need to be PCI-e 3.0 to get 2.0 x16 bandwidth over x8. If it's a 2.0 card, it'll run in 2.0 x8, not 3.0.

Saying that, in reality running 2.0 x8 it shouldn't matter much. Just don't bother with x4.


oops, completely forgot that bit. Tnx for correcting.

My bad, I just got off night shift, so I didnt bother to read the entire post.

Thanks, Zavar

I can move the card to the x 8 slot but at the moment, I have it in the x 4 simply for logistical convenience. What's the problem with x 4? The speed?


Chances are, your card's going to max out the throughput with only 4 lanes. That's only 2GB/s it's got to play with.

It wouldn't be a problem with just browsing around in the OS, but it would limit it in intensive applications.

Thanks. The most intensive app I use is Photoshop. I'll run that for a while and see how it feels in terms of performance.

The x 16 slot issue has got me beat. I've rarely had a problem that I couldn't fix or at least get rid of with a complete tear down and progressive re-build, BIOS update ect etc but so far nothing has worked. The motherboard was bought new in March but so far, I haven't even been able to establish if it's a problem with the motherboard or GPU or simply the combination of the two. I don't see the problem if I just use the on-board graphics but all that does is confirm the problem has something to do with populating that slot.
Thanks again.

i would recommend the top slot since that is usually wired in from the cpu lanes coming from the cpu.

the rest tend to come from the dmi interface.

This should answer your question better than I could word it: https://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/

These types of threads come up a lot. There's a reason I have this link bookmarked.

But yeah. could be a problem with the motherboard itself that is causing the post issue. If you want to rma it that's a good idea, but if you don't want to do that it's fine, you really aren't going to see a difference in performance between the x8 and x16 slots (you'll see this in the link I posted).

The Top X16 slot that is running at 16X speeds.
If you system does not boot, then double check the manual, if the first slot the nearest to the cpu is indeed the 16X slot.
If that is the case, and it doesnt boot with the gpu populated.
Then there might be an issue with the board itself.
In that case you might concider to rma it.