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Confused! Need help!

post #1 of 6
Thread Starter 
Hey OC. I've been looking forward to the moment I'm able to do 3D gaming and have some serious graphics muscle in my home build, and the time has finally come. I've recently purchased 2 EVGA GTX 580 Classified video cards ( http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=1367475&CatId=3669 ) and a second gen ASUS 27" 120Hz monitor. I think I might have a problem, though. The confusion comes from my motherboard and how SLI works. My motherboard says it supports quad-GPU SLI. However, I keep hearing that it will only run SLI in x8 rather than x16.

The spec sheet can be found here for my mobo: http://www.asus.com/Motherboards/Intel_Socket_1155/P8P67_PRO_REV_31/#specifications

My questions are:
1) What exactly will my mobo run my 2 580's at? x8 or x16?
2) If at x8, should I consider getting a better mobo? Will this bottleneck extreme settings or 3D performance?
3) I still have a great working EVGA 560 Ti video card. Can I keep this on the mobo in tandem and have it do the ***** work?


Thanks to all for reading and hopefully my questions aren't too ignorant. I read the SLI FAQ on here but it's a bit outdated although very informative. Also, these cards are going into the build listed in my forum signature. Any help would be greatly appreciated!
post #2 of 6
Hello Renholdt,

That motherboard as well as all p67 motherboards can only run SLI/CROSS FIRE at Dual 8x/8x and not 16x/16x, however from an article I have found ( HERE )with your exact motherboard it is not an issue as the cards do not fully utilize the two slots anyway.

If you look at he specs of that board on the Asus website it states at the very end that:

*1: The PCIe x16_3 slot shares bandwidth with PCIe x1_1 slot, PCIe x1_2 slot, USB3_34 and ESATA12. The PCIe x16_3 runs at x1 mode by default for system resource optimization.(PCIe x1_2 will be disabled.)

And if you download the manual for it it states in the list:

2 x PCI Express 2.0 x16 slots (single at x16 or dual at x8 / x8
mode)
1 x PCI Express 2.0 x16 slot* [black] (max. at x4 mode,
compatible with PCIe x1 and x4 devices)
2 x PCI Express 2.0 x1 slots
2 x PCI slots
* The PCIe x16_3 slot shares bandwidth with PCIe x1_1 slot, PCIe x1_2 slot, USB3_34 and eSATA ports. The PCIe x16_3 runs at x1 mode by default for system resource optimization (PCIe x1_2 will be disabled).

But as I said it should not be a problem as I mentioned two of those cards will not fully utilize the bandwidth available to them.

I hope this helps.
post #3 of 6
Thread Starter 
So current PCI Express 2.0 slots are providing more than enough bandwidth for top of the line cards at the moment? I think it's crazy that dual gpu cards won't use all of that bandwidth. I'm not saying I don't believe you, just learning new stuff here. I read those from the sheet and the manual but I didn't get exactly what it was telling me. Thanks for the quick reply by the way!
post #4 of 6
Thread Starter 
Any thoughts?
post #5 of 6
PCI Express 2.0 @ x16 can provide up to 500 MB/s so at half speed each card still receives 250 MB/s.

Sorry I totally misread your article to begin with(I thought you had two 560s)

A 580 limited to a single 8x slot will loose roughly 4-5% performance (SEE HERE).

So you will loose a little overall 10ish% with two 580s running in SLI @ 8x each.

Personally I think a single 590 would be better in your case than two 580s. But as you already have them you will have to live with the slight performance decrease.
post #6 of 6
Thread Starter 
Thank you very much for the response. smile.gif
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