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I'm looking at this Motherboard: GIGABYTE GA-990FXA-UD7 AM3+ AMD 990FX SATA 6Gb/s USB 3.0 ATX AMD Motherboard and it has 4 PCIe express slots. However, the GPU's that I want are dual slot (Sapphire Radeon HD 7970 OC 3GB DDR5 HDMI/DVI-I/Dual Mini DP PCI-Express Graphics Card 11197-01-40G) and there are 4 of them. So how can I possibly mount this properly? I've considered open air cases, large cases, etc and I'm stumped.

If I get flex cables and risers, then the motherboards just hang out in space. Finally, will the motherboard be able to support 4 GPU's?

I don't want to use SLI or CrossFire. Just 4 independent GPU's recognized by the OS and the MOBO. I'm not using them for gaming. I'm using them for Bicoin mining =)

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closed as too localized by Nifle, avirk, studiohack Aug 20 '12 at 16:48

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1st, 3rd, 5th and 7th PCI-E slot. What's the problem? The manufacturer's website even shows an image. –  Daniel Beck Aug 20 '12 at 15:00
    
Will the mobo allow for 4 GPU's is the other part of the question –  Shamoon Aug 20 '12 at 15:03
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@Ramhound Can't they simply be used independently to power 12 or so screens (without getting better gaming performance)? –  Daniel Beck Aug 20 '12 at 15:19
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@Ramhound: Just because there is no benefit for you or you haven't seen them work doesn't mean there is no benefit for others or others haven't got it working, here is a perfectly working example that has a huge benefit. They can simply address them as 8 GPUs... Or nowadays, 13 GPUs –  Tom Wijsman Aug 20 '12 at 15:24

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up vote 6 down vote accepted

The manual identified by Daniel Beck suggests four dual-width graphics cards can be mounted as shown

Motherboard PCIe slots

The HD 7970 is dual width but uses a sngle slot

HD 7970

Putting a HD 7970 in the bottom slot looks a bit tight to me, with those other connectors under part of the HD7970.

The case also needs to be able to accommodate a dual-width card in that position. It looks rather unconventional to me (but I don't build gaming PCs).

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Note that half of them are 8 and not 16, hence if he wants better performance he might have to consider a newer motherboard. –  Tom Wijsman Aug 20 '12 at 15:36
    
x8 vs x16 will not make much performance difference, but that's technically correct. I think a bigger concern will be power and heat. –  Shinrai Aug 20 '12 at 16:09
    
All four of them will be x8 (Look at manualowl.com/m/Gigabyte/GA-990FXA-UD7/Manual/210504 ) It shows 32 lanes which can be divided either as x16,none,x16,none. Each {x16,none} pair can also be used as {x8, x8}. If he uses four cards then all will work at x8. –  Hennes Aug 20 '12 at 16:17
    
@Shinrai: Is this also true for bitmining? I recall 1% to 4% performance loss from halving the PCIe bandwidth or speed (PCIe v3 vs PCIv2), but that was for gaming. OpenGL was an exception which really liked the lower latency from PCIe V3. (sorry, no link to support that. My google-fu is failing me atm). –  Hennes Aug 20 '12 at 16:22
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Also, note that this board may not be able to allocate this much VRAM properly - you may get PCIe out of resource errors, or initialization problems in the BIOS (in Windows, this would be Code 43) –  Shinrai Aug 20 '12 at 16:58

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