Performance improved by using x8 instead of x16.
Performance improved by using x8 instead of x16.
You're experiencing a mismatch between the reported performance numbers and what your hardware is actually capable of. The CPUID and GPUID indicate speeds of 4.0x8 under load, which aligns with the 16GT/s figure you see on the screen. However, the GPUID shows a lower 4.0x8 instead of the expected 4.0x16, and the BIOS suggests PCIe lanes are limited to 4.0x4 in M.2_1. It seems the CPU's dedicated lanes are being routed to M.2_2, not M.2_1, which is why the PCIe performance drops. You should be able to run the GPU at 4.0x16 and NVME at 4.0x4 in M.2_1, but the current configuration is limiting it to 4.0x8 in M.2_2. Make sure the chipset supports higher speeds and verify the slot assignments.
Verify the connections they use. The highest X16 slot will remain exclusive to X16 operation. Inserting anything into the other X16 slots will lower the top slot down to X8, while the next two slots may drop to X8 or X4 based on what's present. A simple method is to clear all PCIe add-in cards and run gpu-z. If the switch consistently changes between X16 4.0 and X16 1.1, the card is functioning in X16 mode correctly. However, if it only reaches X8 4.0, you should remove whatever is occupying the second X16 slot—no insertions allowed there. If you have SSDs, even on the motherboard, ensure those slots are actually assigned to add-in card positions. Most boards route four lanes from the CPU to the first SSD, the rest to the chipset and operate at 3.0, often cutting SATA connections and reducing USB ports for M.2 devices. The distinction between boards can hinge on whether they use a B or Z chipset. My board is older in that regard. I’m running at X16 but also 16GT. On Reddit, you’ll find similar discussions: https://www.reddit.com/r/overclocking/co...e_v40_x16/. Some users noted they changed power mode to Ultimate Performance, which resolved the issue. One poster mentioned that filling the third M.2 slot with data forces it to X8. Personally, unless you see a need to adjust power settings, the outcome may not differ much between X8 and X16. To test, ensure only one SSD is active—preferably the closest to the X16 slot on Asus models. Then observe if the change occurs. I currently have two PCIe M.2 SSDs installed, one in the chipset and one on the CPU, which confirms what you’re observing.
I only possess one GPU and one NVMe drive. I removed the NVMe and restarted the PC using just the GPU. In the BIOS it still displayed x8. The GPU remains in the highest PCIe lane. It doesn't matter if the NVMe is placed in the M.2_1 or M.2_2 slot, the GPU stays at x8. There are no additional SSDs or PCIe cards installed. All connections on the card appear intact and the GPU is correctly positioned. Note: I inserted a 1080Ti into my PC, which also ran at 3.0 x8, and moved the 3090Ti into PCIe_2, where it worked at x4. So the issue might be specific to the setup. Updated: December 13, 2023 by Lude2Envy