Issue with my GPUs

[blusa]

Hi there, I'm Pablo from Argentina. I'm having an issue with a desktop pc i'm trying to build for my gf. I had laying around an i7-4770k with a maximus vi hero formula, and two gtx 1080 i stopped using.

 

The issue i'm having is that the second card isn't recognized in the BIOS GPU DIMM POST. Basically it shows only the first GPU in the x16 slot. I had a single-slot gt 640 from a nas server i use and decided to chunk it in the third PCIE slot.. and voila... suddenly GPU DIMM POST shows all three cards in x8/x4/x4 config. 

 

I do not understand why this happens and would really appreciate some help from the community.

[jaslion]

Just use a single card. Sli is dead dead dead dead. Nothing new uses it and nvidia officially killed it off 2 years ago.

 

Probably a weird auto config of pcie speed issue with sli active. Not uncommon means you ahve to configure the speed of the ports manually.

 

But as I said sli is dead and the second card will only do more harm than good in the system.

[Zmimgo]

1 hour ago, blusa said:

and voila... suddenly GPU DIMM POST shows all three cards in x8/x4/x4 config. 

There. I don't know what motherboard you have, but simply put, your CPU can only provide a total of 16 lanes to the three slots. Some normal configurations would be like this:

16/0/0
8/8/0

8/4/4

Where the first number indicates the lanes of the first slot, second number on the second slot etc. 

 

Again, depending on your motherboard, it may not automautically do it or do it at all. I would boot into the BIOS and look if there is any manual mode for splitting PCI-e lanes between the three slots.

 

Also, just answering a few common questions since they may come up:

 

Q: Can I use 16 lanes on all three slots?

A: No. Your motherboard rewires the lanes that come directly from the CPU, so you would need a slot connected to the chipset (where the connection would be around 4 lanes maximum). If your motherboard had a PLX chip specifically for sharing the bandwidth between slots, then it would work. (but just give up on that)

 

Q: Can i use the second/third slot at 16 lanes?

A: Typically on consumer platforms, no. This is because those PCI-e 16x slots usually actually only have contact pads for 8 lanes. Unless you reengineered the motherboard you wouldn't be able to get 16 lanes on the non-main slots.

 

Q: Where do I find the BIOS setting mentioned earlier?

A: idk check ur manual lol

[blusa]

Hey guys, thanks for your replies... The idea was not to use SLI but to use both cards separately. She uses some design/architectural software suites that apparently benefit from having several gpus. I am still stuck in x16/x0/x0 or x8/x4/x4 and cannot move to x8/x8/x0. I guess I will end up buying some bluetooth or nvme adapter and use that third PCIE slot..

[Mick Naughty]

Could reseat the cpu. The board should work all the same regardless. 

I had the same issue where I had to put a third card in the bottom slot to get the other cars to work again. But I wash flashing bios's on them. But it its working now, the last slot will just have a limitation with total drives being used. I dont recall what the integrated Bluetooth/wireless adapter ties into.