Folding Forum

I couldn't find it in the documentation so this is partly guesses.
I have a sabertooth 990FX motherboard with 4 16X pcie slots
Nvidia gtx 1080 GPUs will run in three of the slots but not in the fourth. My assumption from what I've read is that the fourth slot has only 4 lanes and some GPUs won't start with only 4 lanes.
An nvidia gtx 960 GPU will start in the fourth slot.
Since I'd like to maximize the output from this folding rig, does anyone know what Nvidia GPU has the maximum performance that will start with a 4 lane pcie slot?

To be honest, I don't really expect an answer but thought I'd give it a shot.
It just occurred to me that I should go to the source and ask Nvidia support.

That sounds strange, any GPU should start in a x4 speed slot?! With "start" you mean it is recognized in Windows as device? Or in FahClient?
Does it not start when 4 GPUs are put in or does it also not start when only gtx 1080 is put in x4 speed slot?

Yeah, a card should work in any slot. I run 1080s in 4x slots and have tested them on 1x risers just fine.

How many cards are you trying to run at once? Looking at the slot spacing on the Asus website, I can't see how you could fit more than 3 without risers - if so, are they good?

It's possible the board can't supply enough power to all of the slots - some have additional power connectors to supply the PCIe slots, but that is a decent board and wouldn't think it would have problems.

Thanks for the responses. It's under Linux Mint if that matters. Right now I have 4 GPUs folding fine, 3 1080s and 1 960. The spacing works because it's an open air "case" which is also nice as everything runs cooler. I use top quality 16X shielded risers. I don't think it's power as it's a top quality 1000 watt power supply and my killawatt says with the 4 gpus i'm running that I'm using 730 watts so minus 85 watts for the 960 I should have available up to 355 watts which should be way more than enough. Also it's only a problem on one specific slot. If it was power I think all the slots would be flaky. Yes by "start" I mean recognized as a device. It doesn't show up in psensor which displays device temperatures and fan speeds and such.


3 x PCI Express 2.0 x16 slots (Dual at x16/x16, triple at x16/x8/x8 mode)*
1 x PCI Express 2.0 x16 slot (Black@x4)
2 x PCI Express 2.0 x1 slot

It's the black 4X slot that is giving me the problem.

The 1080 that wouldn't boot on the X4 slot works great on a different PC

I was basing my theory on a post I found elsewhere that some gpus wouldn't boot at all on x4 slots.

Are these 16x-16x powered risers?

So unpowered risers. What the actual MB model
I've got a Gigabyte 990FXA-UD7 MB that will not recognize more than 4 cards in its six x16 slots. Their spec does not give a clue and Gigabyte does not respond in their forum. The only response I've gotten so far is, "The FX990 northbridge has 32 usable PCIe lanes on this motherboard. It is the most for any AMD board. So you are running out of lanes since video cards want to run with 8 lanes."

SABERTOOTH 990FX R3.0
The slot lane specifications are in an earlier post above from the motherboard's manual.
I have had as many as 5 gpus recognized at once by this motherboard. 3 1080s 1 960 (in the black slot) and one 750ti on an x1 slot. Again, the issue here is what is the most productive gpu I can put in the X4 black slot which won't support a 1080. The 960 works great in the black slot along with three 1080s in the other x16 slots running as 16/8/8. Granted it may not make sense to upgrade the 960 anyway, depending on price and output.

Steve, How about a 1070? I got confused because if a 1080 won't run in the slot why would a 1070? But you say a 960 runs fine.
In the other forum folks were reporting their tests on various cards:
viewtopic.php?f=38&t=28847&start=75#p291931

Thanks for the link. It looks like tests were done on a 1070 at 1x which is encouraging but I see another test where they ran a 1080 at 1x, so I don't know what to think. If I got a 1070 and it didn't work on the 4x slot I don't have anywhere else to put it. Well, since I just bought a 1080 I have to wait at least a month to spend the money so I have time for more research.

Power the riser and it "should" work. Despite what anything says "on paper", these cards pull power through the mb and, in some cases, it's more than the mb can supply. The "rule of thumb" for mining used to be 4 or more need power, but I've found that with some motherboards, 3 is too many without any surplus power for a 1080.
If you're feeling brave enough to try your own hand at it, here's an example: https://bitcointalk.org/index.php?topic=76121.0

Only thing, the 1080s work fine on the other slots of this motherboard with unpowered risers. But yes, I know they pull power from the slots because the fans come on even without the power cables hooked up.

SteveWillis wrote:Only thing, the 1080s work fine on the other slots of this motherboard with unpowered risers. But yes, I know they pull power from the slots because the fans come on even without the power cables hooked up.

OK, let me give you a real world example (and see if this makes sense):
Asus Z170-E
2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
1 x PCIe 3.0/2.0 x16 (x2 mode)


You can put 3 1080s directly into the board and it fires off fine.
You can put 1 unpowered* 1080 into any slot, 2 1080s directly into the board, and it fires off fine.
You can put 1 unpowered 1080 into any dual x8 slot, 1 unpowered 1080 into the x2 slot, 1 1080 directly into the board, and it fires off fine.
You can put 2 unpowered 1080s into the dual x8 slots, 1 1080 directly into the x2 slot, and it fires off the x2 only.
You can put 3 unpowered 1080s and usually not even get POST.


*unpowered = using an unpowered riser

OK, thanks!

Where is a good source? All the ones on Amazon look like junk.