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  GTX580s in SLI bottlenecked on Z68? 
 
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Seth Hoffman Apr 09, 2012, 10:37am EDT Reply - Quote - Report Abuse
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Edited: Apr 09, 2012, 10:42am EDT

Replies: 3 - Views: 2577
I have recently been reading the previews for Z77 and Ivy Bridge and I got to thinking about PCIe 2.0.

Has anyone seen benchmarks comparing GTX580 SLI on two x8 PCIe 2.0 slots versus two full x16 PCIe 2.0 slots?

A full x16 PCIe 3.0 slot has 16GB/s full duplex throughput. A full x16 PCIe 2.0 slot has 8GB/s full duplex throughput. When running in SLI on PCIe 2.0 this splits the lanes so one card has a x8 slot and the other has a x8 slot, allowing for 4GB/s full duplex throughput for each card.

Does this make a difference? I am interested because I have no real interest in Z77 or Ivy Bridge other than potentially upgrading for PCIe 3.0 to increase throughput to the video cards. The new Ivy Bridge processors still only support 16 lanes of PCIe, but they're 3.0 spec. This allows for even a x8 slot to run at the same throughput as a PCIe 2.0 x16 slot. PCIe 3.0 doubles the through put for each lane from a 2.0 spec of 500MB/s to 1GB/s



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Seth Hoffman Apr 09, 2012, 10:48am EDT Reply - Quote - Report Abuse
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Edited: Apr 09, 2012, 10:49am EDT

 
>> Re: GTX580s in SLI bottlenecked on Z68?
From what I've been reading in quick google searches, there is about a 3FPS difference between 8x/8x, 16x/16x.

Anyone have first hand experience with this?


Meats_Of_Evil Apr 09, 2012, 03:02pm EDT Reply - Quote - Report Abuse
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>> Re: GTX580s in SLI bottlenecked on Z68?
From what I've read also the difference is minimal so I'd say you don't need to worry about it but the word still applies since the card isn't performing at its max but then again, the loss in performance isn't as drastic as the word implies.

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Bungle Apr 24, 2012, 03:21am EDT Reply - Quote - Report Abuse
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>> Re: GTX580s in SLI bottlenecked on Z68?
This is an educated guess, but I imagine that loss of performance due to PCIe bandwidth is probably dependent on the game. If the card is constantly swapping textures out of (system) RAM then a slow PCIe bus will likely have a big impact on performance, if the card has enough video RAM to store everything it needs so that it doesn't need to page its data to your system RAM then the difference is probably not a whole lot.

Does this make a difference? I am interested because I have no real interest in Z77 or Ivy Bridge other than potentially upgrading for PCIe 3.0 to increase throughput to the video cards.


If you're going to do that you might as well step up to an x79... That platform is so much more robust when it comes to mulitple video cards and since you'd be buying a new motherboard and CPU anyway the cost difference wouldn't be very much.

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