PCI_E x16 & x8 question

bdriskill · Apr 6, 2011

I have a M4A89GTD PRO/USB3 with 2x x16 pci slots but when running x16 on the bottom one the top will drop to x8. In crossfire they will both drop to x8

Is it even worth going xfire on this board? :-/

TheQuadFather · Apr 6, 2011

yep, you wont notice a difference at all, cards lose about 3-5% bandwidth, you can run cards at x1 with minimal issues, theres a test somewhere which i might dig up later if i have the energy.

ratbuddy · Apr 6, 2011

While there is a significant performance drop at x1, x8 will be fine.

bdriskill · Apr 6, 2011

ahh thank you i might have to go ahead with it then. I currently have a 6950 and was going to save up for the 6990. But 2x 6950s are still cheaper and out perform the 6990

tool_462 · Apr 6, 2011

For what it is worth, here are some real numbers for you to digest:

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html

1-2% performance loss.

TheQuadFather · Apr 7, 2011

ratbuddy said:
While there is a significant performance drop at x1, x8 will be fine.

running a hd5870 at x1 only lost 25% performance, so really its not as catastrophic as you thought.

ratbuddy · Apr 7, 2011

TheQuadFather said:
running a hd5870 at x1 only lost 25% performance, so really its not as catastrophic as you thought.

It's exactly as catastrophic as I thought, I've read those articles several times in the past.

TheQuadFather · Apr 7, 2011

ratbuddy said:
It's exactly as catastrophic as I thought, I've read those articles several times in the past.

well what i was trying to say was, a x16 drop in pci-e speed doesnt equal a x16 drop in performance.

QuietIce · Apr 8, 2011

bdriskill said:
I have a M4A89GTD PRO/USB3 with 2x x16 pci slots but when running x16 on the bottom one the top will drop to x8. In crossfire they will both drop to x8

Is it even worth going xfire on this board?

Most boards (even Intel) don't have enough PCIe lanes to support true 2x16 PCIe slots. AMD's FX chipsets have 40 PCIe lanes and can support it but none of the other AMD boards have that many lanes (Intels don't even have that many). That being said, and as has been said, it won't make that much difference in performance. I'm sure, eventually, they'll have video cards where it matters but, for now, it's virtually nothing.

PCI_E x16 & x8 question

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