Any difference for GTX 670 SLI in PCIe 16/16 vs PCIe 16/8 ?

[poohbear]

Hey all, i wanna get a Z77 mobo with GTX 670 (using PCIe 3.0 as i'll have an Ivy bridge) and hopefully grab another one for SLI 1-2 years down the road. My questions is, does having a SLI mobo that has 16/16 PCIe lanes (high end expensive mobos) VS 16/8 PCIE lanes (most mobos) really hinder performance? Is 16/8 (in PCIe 3.0) more than enough for GTX 670 SLI or will the lanes get saturated bandwidth wise?

Thanks in advance!

 

[cmdrdredd]

Well, before I answer you I have to clarify. No board runs 16x/8x

The options are 16x/0x or 8x/8x and for 3+ slot configs you can do 16x/0x/0x or 8x/8x/0x or 4x/4x/4x unless there is a PLX chip to add extra PCIe lanes.

So when you run a single 670 you are getting PCIe 3.0 16x and when you run two you get PCIe 3.0 8x and 8x. PCie 3.0 8x is the same as PCIe 2.0 16x and the GTX 670 won't be close to maxing out the bandwidth so to answer directly, no there is no worry about it being a problem or slowing anything down.

 

[borisvodofsky]

for the last time, Nooooooooooooo

 

[Grooveriding]

2-5% difference between 8/8 and 16/16.

It only starts to get notable with three or more cards and at higher resolutions.

Nothing to go crazy over.

 

[biostud]

2-5% difference between 8/8 and 16/16.

It only starts to get notable with three or more cards and at higher resolutions.

Nothing to go crazy over.

and probably even less since the bandwidth of PCIe 3.0 8x/8x = PCIe 2.0 16x/16x

 

[Shmee]

I imagine, though, for GTX 690 quad SLI it could be an issue? How much would an 8x PCIE3 slot bottleneck said card?

 

[PowerK]

OP,
This should be a good read for a single graphic card.
Ivy Bridge PCI-Express Scaling with HD 7970 and GTX 680

and probably even less since the bandwidth of PCIe 3.0 8x/8x = PCIe 2.0 16x/16x

Not quite.
PCI-E 2.0 has about 20% overhead (due to 8b/10b encoding) and PCI-E 3.0 has about 1.5% overhead. Entire frames of alternate frame rendering are sent over the PCI-E bus at high speed. This is a lot of traffic when you get into 3-Way, 4-Way and/or Quad-SLI configurations.
However, I think 4.0 GB/s bandwidth of PCI-E 2.0 x8 should be enough for 2-Way SLI setup. I'd be very surprised if two entire frames of alternate frame rendering data exceed 4.0 GB/s of bandwidth. Also, we have a SLI bridge connection.

Anyway, someone at overclock.net did some PCI-E 2.0 vs PCI-E 3.0 test with 680 4-Way SLI setup.

From : http://www.overclock.net/t/1220962/...nd-computer-edition-2012/360_20#post_16915399

 

[cmdrdredd]

I imagine, though, for GTX 690 quad SLI it could be an issue? How much would an 8x PCIE3 slot bottleneck said card?

Maybe, but i haven't ever seen a test like that

 

[IGhzI]

Linus from ncix says yes there is a difference but nothing worth spending the money over... the video is in his YouTube channel

 

[poohbear]

Thanks for the info guys! lol i certainly wont be going tri or quad sli, 2 cards is more than enough!

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