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What does it mean that a "PCI-Express 3.0 X16 Slot runs at X8"?

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December 15, 2012 12:58:13 AM

Thinking about buying the ASrock Extreme4 for my computer. However, under slots on the amazon page it says
"2X PCI-Express 3.0 X16 Slots (runs at X8)"

What does this mean? I don't want to buy with knowing what I'm buying.
Thanks.

PS here's the page for full context.
http://www.amazon.com/LGA1155-CrossFireX-Motherboard-Z7...
a b V Motherboard
December 15, 2012 1:12:27 AM

It mean the slot are full length (i.e. video cards) but run at half that, because it's sharing bandwidth ("lanes") with other slots/devices. Pretty common.
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December 15, 2012 1:15:09 AM

How do they run at half length?
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a c 81 V Motherboard
December 15, 2012 1:15:10 AM

It probably meant 8x/8x dual mode, the pcie 3.0 slot single is at 16x, single at x16 (PCIE2) / x8 (PCIE3)
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a b V Motherboard
December 15, 2012 1:18:12 AM

Sorry, meant it's running at the speed as if it was half that length.
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December 15, 2012 1:25:55 AM

So how much of an effect will that have on the video card's performance?
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Best solution

December 15, 2012 1:34:32 AM

Next to none. Until you get down into PCIe 1 or PCIev2 x4 you aren't going to see any drops.
Here's a link that shows the effects,

http://www.techpowerup.com/reviews/Intel/Ivy_Bridge_PCI...
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a b V Motherboard
December 15, 2012 8:07:17 AM

+1
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a b V Motherboard
December 15, 2012 8:34:23 AM

Gpu set up look like this. 1x gpu=x16; 2x gpu=x16+x16=(x32); 3x gpu=x16+x8+x8=(x32); 4x gpu=x16+x8+x4+x4=(x32). so 2xgpu=4xgpu. So insert the gpu in x16 slots.
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December 16, 2012 4:42:36 AM

Best answer selected by RS13.
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