Question GPU performs much worse in x16 slot than in x4

Aug 11, 2020
Hi guys, I'm a bit stumped here.

I think the title is self explanatory, but here's my setup:

Ryzen 1600x;
RTX 2060 Super;
16GB RAM at 2400 MHz;
Gigabyte AB350-Gaming 3.
Games and apps installed on an M2 drive.
BIOS version is 28 (most current one is version 51, but I've seen no reason to flash my BIOS, as none of the updates have any features that would benefit me).

While I was aware that for optimal performance the GPU should be in the top PCIE x16 Gen3 slot, I'd never given it much thought. I had originally and absent-mindedly put the card in the bottom PCIE x4 Gem2 slot (stupid, I know) and it has always worked just fine with modern games.

Recently Horizon Zero Dawn came out and it was running quite poorly. Some people said that it's a fussy console port and requires all the extra lanes, so I popped my card into the x16. Suddenly from a badly fluctuating framerate (anywhere between 60 and 5 FPS) in the bottom slot, I was now getting only single digit frames in the top slot. Confusing, so I checked Death Stranding and Witcher 3, both of which also ran noticeably worse.

This didn't make any sense to me. I checked HWinfo and it confirmed that it's in the x16 slot and running at x16 lanes. When in the bottom slot, it confirmed that it was running at x4, so HWinfo was sensing the changes correctly. I've also never changed any settings in the BIOS, but just to be sure, I set it to default settings.

I haven't got much experience in this area, as you can probably tell, so I'm utterly confused as to why games are running so much worse in what's supposed to be the optimal PCIE slot, especially since HWinfo is confirming that it's running at the correct bandwidth, and not at something like x1 or x2.

The manual for the motherboard was also not helpful and the Gigabyte UEFI BIOS user interface is a stylish "gamery" mess that doesn't make it clear if any if my settings are wrong. At one point I forced the PCIE slot to be on Gen3 instead of Auto, but that didn't make a difference so I set it back to default again.

This is not a critical issue, but I would appreciate any advice. Mostly for improved gaming performance, but really because this issue is confusing the hell out of me and I'd like to learn what I'm doing wrong so that I don't repeat it in the future.

Cheerio 👍

P.S. The above mentioned games also all load quite a lot faster when the GPU is plugged into the PCIE x4 Gen2 slot than in the x16 Gen3 one. Like 2-3 times faster. Why?
Aug 11, 2020
Thank you for the suggestion. I'm however even more confused now. I reseated the CMOS battery and that seemed to fix the problem for both Death Stranding and Horizon Zero Dawn. "Great!", I thought. They were both loading fast and running at a consistent 60FPS (not HZD, but that's a whole other issue), as they were doing in the x4 slot.

That is, until I loaded up the games a second time. Death Stranding started taking longer to load again and when i got in the game it was fluctuating between 20-40 FPS, same as before. Witcher 3 seemed to run fine except with a constant microstutter every 10 seconds or so - an issue I've never had with x4, but have always had with x16.

I'm tempted to assume that my mobo is faulty, but then why did Death Stranding run considerably better the first time I loaded it up and then it didn't the second time? Why did it solve the issue for just one round of loading up the game?

P.S. This might be in my imagination, but my mouse cursor seems to stutter quite a lot and struggle to catch up every time I put the GPU in the top slot, even if I'm just on my desktop. Again, what?


Dec 4, 2016
I would update a BIOS anyway, format ssd/hdd with clean installation of windows.

Then install the drivers etc. and try. I think its the only solution before changing the hardware.
Aug 11, 2020
Okay, updated BIOS, formatted all my drives, new Windows installation, got all the latest drivers and the issue is persisting.

What I find odd is that when I plug the GPU into the top slot, HWInfo says the following:

PCIe v3.0 x16 (5.0 GT/s) @ x16 (2.5 GT/s)

but on the rare occasion it says

PCIe v3.0 x16 (5.0 GT/s) @ x16 (8 GT/s)

The latter would seem to suggest that sometimes it wants to run at 8 gigatransfers per second, but 90% of the time it wants to run at 2.5 GT/s, which is the default for the bottom (x4) PCIE slot.

What does this all mean? Why is it also making games load much slower, besides running them worse?

It's likely that my motherboard is busted, but I'd like to be sure of that before I invest in a new one. I'm close to pulling my hair out here in confusion.