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3 or even 4 GPUs on mobo that only supports two?

Tags:
  • mobo
  • multi-GPU
  • motherboard compatibility
  • SLI
  • Motherboards
  • GPUs
  • r9 290x
Last response: in Motherboards
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October 6, 2014 12:00:58 AM

Good day,

I have read the entire manual for the GA-990FXA-UD3 v.4.0, and I have asked many competent people about this, and searched overclocking and gaming forums, but to no avail.

I normally run two R9 290X video cards directly attached to both PCI 2.0 x16 slots (so, PCIEX16_1 and PCIEX16_2) and my system has never had any issues. However, since I like tinkering, and since this motherboard is beyond any warranty period, I figured I would try to insert a third R9 290X GPU on the PCIEX4_1 with a powered riser cable as to not fry the 24-pin ATX connectors. It worked! I ran it through hours and hours of benchmarks (Unigine Heaven 4.0, Unigine Valley, 3D Mark Extreme, Firestrike Extreme, Catzilla, Geekbench, etc. and several games like Metro Last Light Redux) for many days, and it all worked fine. 3-way Crossfire shows up in GPU-Z and Catalyst Control Centre, and all three GPUs were at 100% load during these benchmarks, so I know for certain that all three were working.

If I use NON-powered cables, my system becomes very unstable and will crash within minutes.

My question is - given that I was able to make a 2-way-rated mobo work with a third GPU using a powered riser (it was not sucking any power from the mobo), is the main difference between the UD5 and UD7 mobos their ability to natively support a third and fourth, respectively, without the need for powered riser cables?

I love this board, thank you so much!

More about : gpus mobo supports

a c 367 V Motherboard
October 6, 2014 2:01:24 AM

UD5 has the ability to support 3 way SLI/Xfire without powered riser cables.

UD7 has the ability to support 4 way SLI/Xfire without powered riser cables.
October 6, 2014 9:19:18 AM

So did I just accidentally discover a way to make any "2-way SLI/Crossfire" mobo work with 3 or 4 cards?
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a c 367 V Motherboard
October 6, 2014 9:22:47 AM

I think you might have, But I don't really see it coming into fashion. The slot bandwidth is too low to for people to consider.
October 7, 2014 8:18:01 PM

Just tried it with four GPUs (GPU 3 and 4 are powered by their risers whose 12v wires get power directly from the PSU) and though it lengthens the computer's booting time by about 25 additional seconds, all four GPUs do work, and do contribute to generating the graphics.

However, the difference between 3 and 4 GPUs, at least on my computer, gives a mere 3% improvement in Unigine Heaven 4.0.

Also, the fourth GPU produces a loud, rattling noise which is not coming from its fan. The card is physically fine though... could be the PCI-E 2.0 x4 slot throttle it down like crazy.
a c 367 V Motherboard
October 7, 2014 9:48:05 PM

doesn't sound healthy, and doesn't sound like the slot limiting the card to make that noise either.
a b V Motherboard
October 7, 2014 9:56:16 PM

3% increase. Considering the price of a 290x, for the extra 2 fps on a 60Hz 1080p monitor that never get seen, I doubt many will try the powered riser sli that you tried.
!