PCI-E Running at x8

[Lude2Envy]

I just replaced my Firecuda 530 with a Samsung 990 Pro. I have a Z690 Extreme MB. I've been reading some conflicting information online. Some are saying with the 12900K's 20 PCI lanes you can run a GPU at x16 and the SSD at x4 in the 2_1 slot, so I first put the 990 in the 2_1 slot. I noticed in CPU-Z that my "link width" on the MB tab is showing x8. I moved the 990 to the 2_2 slot and it's still showing x8 in CPU-Z. I don't have any other drives or PCI devices installed so this leaves me with 2 questions:

1. Can you run a 3090Ti at x16 with the SSD in the 2_1 slot and if so, what was I doing wrong?

2. If the GPU will drop to x8 with the 2_1 slot occupied, why am I still showing x8 in CPU-Z?

Thanks in advance!

[Jiaszzz_ROG]

Hello, @Lude2Envy 

According to the ROG MAXIMUS Z690 EXTREME user manual page xiii, the explanation for PCIe and M.2 sharing channels is as follows:

Therefore, we recommend installing the graphics card in PCIeX16 (G5)_1 and the SSD in M.2_1.
At the same time, please verify whether there is a need to update the BIOS and check again after clearing the CMOS.
If the problem persists, could you please provide the GPU model, BIOS version, the currently manually adjusted BIOS settings, and screenshots of CPU-Z?

Thank you.

[Lude2Envy]

I took the SSD out and booted into the BIOS with just the GPU to make sure no lanes were being shared and it still only registers at x8. The BIOS is updated to 2802 and I tried clearing the CMOS and loading optimized defaults. Still only x8. Cleaned the pins on the GPU and triple checked that it's seated properly in the PCIe_1 slot. Never used the second slot. The GPU is a EVGA 3090Ti FTW3 Ultra. No BIOS settings are manually adjusted at this time, but I did try assigning the lanes manually to gen 4 and even gen 3. It still only registers at x8 every time. Screenshot is below.

Edit: I have a 1080Ti in another computer that runs fine at 3.0 x16. I put it in my computer and it's stuck at 3.0 x8. I guess either the CPU or MB are bad, or there's a flaw somewhere in the BIOS that's blocking those other 8 lanes. I also moved the 3090Ti to the second PCIe slot. It ran at x4 in that slot.

[Jiaszzz_ROG]

Hello, @Lude2Envy 

Thank you for providing the updates and details.
May I inquire if adjusting the "PCIEX16_1 Link Speed" in BIOS under "Advanced > System Agent (SA) Configuration > PCI Express Configuration" to [Gen 4] helps in resolving the issue?
Have you attempted cross-testing the EVGA 3090Ti FTW3 Ultra with another board or tried installing a different GPU to narrow down the possibilities?

Thank you.

[Lude2Envy]

The link speed in the BIOS is just that.....link speed. It has nothing to do with number of lanes. Link speed is based on the PCIE generation. Lanes used is irrelevant of generation. The PCIE port is running at Gen 4 speeds like it's supposed to. It's the  number of lanes being utilized that's the issue.

I did try a 1080Ti from another system that I know works - as I mentioned in my previous post. I had the same issue.

I sent the motherboard in for RMA. They sent me a replacement. The issue is resolved with the new board so something was wrong with the old board.

[Jiaszzz_ROG]

Hello, @Lude2Envy 

Thank you for the update, and I'm glad you were able to narrow down the issue.
If you encounter any difficulties or concerns, please feel free to DM me with detailed context at any time.

Thank you.

[Lude2Envy]

Thank you!

[rangermiranda12]

I recently had the same issue where no matter what configuration i used i couldnt get my 4090 to run at x16.  I set up and RMA and motherboard was replaced within a week and a half.  Now I am running full bandwidth on my 4090 which I would tell people is very noticeable when running 3 monitors as I do.  No more constant flikering when doiong certain tasks.