Can't see my second GPU on new z790 Dark Hero

[Ike_Star]

Hello all!

I just built a new system with a Maximus Z790 Dark Hero.

It is to be used as a 3D Render Machine, so it has 2 4090  Video cards.

No matter what I do, it will not recognize the GPU in the second PCIEX slot.

Both work in the primary slot (keeping their power cables, so that doesn't seem to be significant).

I also tried each one by itself in the second slot, and nothing!

Anyone have any Ideas? 

Thanks, and let me know if there is and other information to post!

[Wesley1 · Accepted solution]

It might be that you're PCIe lines limited and therefore there isn't enough free PCIe lines for second GPU.

The Z790 should support 16 PCIe lines for GPU and 4 PCIe lines for NVME SSD.

The manual for your motherboard says differently. I'm not sure if is is an error in manual or actual motherboard limitation.

If you have NVMe SSD above your first GPU card (M2_1 socket) you might need to move it below to M2_2 socket which is connected to motherboard's chipset.
Performance wise you should not notice much difference in regular work, I'm not sure how it will be with rendering stations.

Before you change anything try to look up BIOS setting that changes PCIe. I could be named "PCIe Bandwidth Bifurcation Configuration" of similar. On some boards it allows to set 8x/8x/4x (GPU/GPU/SSD).
The manual for your motherboard say it is either 8x/8x or 8x/4x, that is GPU/GPU or GPU/SSD.

Probably for workstation you should went with AMD, they are more generous with PCIE lines on top of the line motherboards.

From Z790 DARK HERO manual

[Ike_Star]

Thanks for the reply Wesley!  I'll check this out, and update!

[Ike_Star]

Wesley, you were dead on, thank you so much for your help!  Switched from the First M slot to the second for my HD, and it worked! Thanks again!

[Wesley1]

No problem. I'm glad it worked out for you. 🙂