Can An Overclocked GTX 690 be bottlenecked by PCIe 3.0 or PCIe 2.0 x16 ?

apoppin · Posted: Sat Jul 28, 2012 9:31 am

They sure have it wrong over there including Russian Sensation
http://forums.anandtech.com/showpost.ph ... tcount=199

Quote:

modern Z77 boards have 8x / 8x configuration. Each PCIe slot delivers that. So if you run 1 card on each of those slots, it should make no difference at all that those benchmarks by TPU use 1 GPU, since both GPUs will get PCIe 3.0 x8 which is pretty much identical to PCIe 3.0 x16 per benchmarks. Even in older Z68 boards, that'll still be PCIe 2.0 8x per GPU, and that amounts to approximately a 2-3% difference, nothing worth talking about.

The PCIe 2.0 x8 vs. PCIe 3.0 x16 hasn't been shown to be an issue in any credible review.

Ocre · **Joined:** Mon Nov 22, 2010 5:22 am **Posts:** 2234

no kidding

apoppin · Posted: Mon Jul 30, 2012 4:14 pm

How can i test this on my EVGA z77 FTW MB?

It features a full 16x+16xPCIe SLI lanes due to the plx chip in the MB; up to 3 x 16x PCIe 3.0, i believe.

SickBeast · **Joined:** Sun Jul 20, 2008 11:57 pm **Posts:** 4301

That's a lot of lanes. You would have to test it against one of those quad SLI boards that only do x8/x8 or even x4/x4 if you want to be more thorough.

apoppin · Posted: Mon Jul 30, 2012 8:59 pm

SickBeast wrote:

That's a lot of lanes. You would have to test it against one of those quad SLI boards that only do x8/x8 or even x4/x4 if you want to be more thorough.

Actually, here are the details of the PCIe lanes (i am fact-checking now )

Quote:

Quote:

Expansion Slots

PCI Express 3.0 x16 = (1x16 or 5x8)

PCI Express x1 = 1

SickBeast · **Joined:** Sun Jul 20, 2008 11:57 pm **Posts:** 4301

40 lanes is lots of PCI-E bandwidth. It seems silly that they don't offer x16/x16 though.

apoppin · Posted: Mon Jul 30, 2012 9:35 pm

As i understand it, this 'extra' bandwidth is provided by the PLX chip - however, the CPU still only has 16x lanes devoted to PCIe - total
-- the PLX chip is much like USB where there is a *total* amount of bandwidth available. For example, connecting 2 USB 3.0 devices to a hub using a single USB 3.0 port, the maximum bandwidth is the same as 1 USB 3.0 port.

PLX is a PCI-E switch that allows you to connect 2 or more PCIe devices to 1 PCIe port and since the upstream CPU to PLX port is x16x, 16x is also the total bandwidth available to the 2 or more downstream GPUs. As i understand it, using the PLX chip will give similar performance to connecting the GPUs directly to the CPU although the PLX chip has some overhead as well as latency to deal with and you will get less bandwidth (than say X79 MB that has more PCIe 3.0 bandwidth).

i am doing further research and finding conflicting info. i'll contact the EVGA rep tomorrow for clarification .. but this is what i also have found

Quote:

1 Card: x16
2 Cards: x16 – x16 (Slot 2 & Slot 4)
3 Cards: x8 - x16 - x16
4 Cards: x8 - x16 - x8 - x8

i hope it is the above configuration
:hello:

Can An Overclocked GTX 690 be bottlenecked by PCIe 3.0 or PCIe 2.0 x16 ?

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