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Performance Decrease PCIe 2 x8 vs PCIe2 x16

post #1 of 4
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hey there,
so i've sized down my rig from a the huge HAF Advanced to a reasonably sized FD Arc Mini, as the HAF was too big and too hard to get quiet, with all the meshes and the general material of the case.

Due to budget constraints (and because i heard that its quite a fine motherboard) i went with the Asrock z77 extreme4-m instead of the P8Z77M-Pro and for now im very pleased with all aspects. As i left the realm of watercooling for now im sticking with my old Prolimatech Armageddon mounted by a push pull configuration of 140mm fans. My problem now is that the Armageddon is too wide for the mainboard to allow me to use the first PCIe Slot for my HD7950. Now im still on my 2600k, no Ivy Bridge+ here yet and so im "stuck" with PCIe2.

So I will using the second PCIe slot (PCIe2 x8) give me a noticeable (and if measureable, how much?) performance deacrease over x16?

PS.: sorry for repost, but after looking for it i didnt find a satisfying answer.
Edited by muselmane - 7/13/13 at 6:50am
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No turn unstoned
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post #2 of 4
Minimal performance drop won't be noticeable.
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post #3 of 4
1% in FPS loss biggrin.gif
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post #4 of 4
Those over at the notebookreview.com forums doing eGPU contraptions were testing that a lot. They were noticing at x1 v2 a performance of something like 50% that of x16, at x2 v2 around 70%, at x4 v2: around 85% and at x4 v3 around 96%. Since x4 v3 = x8 v2 then you're looking at around 4% drop.

What people out to know is that PCI-E almost never saturates during rendering but it can always use more lanes. Most games nowadays upload the bulk of what is needed before even starting rendering so what you need more lanes and bandwidth for is not for the 'bulk' but for the speed.

So even with 999 lanes we'd see an improvement. Of course, it might be minimal after a point since there other bottlenecks.

So don't be fooled, 16x is not the "max", it's just the max available.
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