PCI-e x16 and x4?

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plutoniumman

New Member
Hi all :)

I’ve been looking at motherboards, and noticed [URL="http://www.newegg.com/Product/Product.aspx?Item=N82E16813130290”]boards like this one[/URL] have a PCI-e port at 16x and a second port at 4x. Does this mean the graphics card in the first port will run full speed, and the graphics card in the second port will run 400% slower?

I tried searching the forums & google for this subject, but couldn’t find much... Probly due to the fact I’m not sure how to go about searching for it.

EDIT: Just came across the MoBo 101... So PCI-e x4 really does have 400% less bandwidth than PCI-e x16? Does the severely effect CrossFire or SLI performance?
 
Last edited:
plutoniumman said:
Hi all :)

I’ve been looking at motherboards, and noticed [URL="http://www.newegg.com/Product/Product.aspx?Item=N82E16813130290”]boards like this one[/URL] have a PCI-e port at 16x and a second port at 4x. Does this mean the graphics card in the first port will run full speed, and the graphics card in the second port will run 400% slower?

I tried searching the forums & google for this subject, but couldn’t find much... Probly due to the fact I’m not sure how to go about searching for it.

EDIT: Just came across the MoBo 101... So PCI-e x4 really does have 400% less bandwidth than PCI-e x16? Does the severely effect CrossFire or SLI performance?
Click to expand...

The link is broke, but with boards that have 1 x16 and 1 x4 port will still work with crossfire/SLI, just some graphics cards won't perform to their full potential due to the bandwidth limitation of an x4 lane.

If you are using say 2 GTS250's, or 2 HD4850's, you shouldn't have a problem with x4, it might lose a bit of performance, but not a whole lot.

Just because the x4 lane has less bandwidth, doesn't mean the card will run at 25% speed. Think of it like a road, versus a 4 lane highway. Just because the highway has 4 lanes, doesn't mean it will always have 4 times as much traffic as the road, and it doesn't mean the road will always be full and at a standstill, 5 cars on 1 road won't be slowed down, 5 cars on a highway won't be. But, there comes a point, say at 50 cars on 1 road, when the road can't handle that many, but the highway can.

It is the same for the PCIe lanes, just because the x4 has less bandwidth doesn't mean that it will always be running slower, it just means that it will be a bottleneck before the x16 lane will be
 
Thanks for the reply :)

How do I know if a board will support SLI or crossfire or not?

This board here:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131636
Has the word SLI in there, but it doesn’t have 30 logos of NVIDIA like other boards that obviously support SLI. (ie it’s one of the main selling points)

Would it be a bad idea or disadvantageous to use NVIDIA’s SLI on an AMD board? I mean like would AMD/NVIDIA be jerks about it and for some reason throttle down performance, or something like that? Sorry I’m asking all these questions and not looking it up myself... Have to go to work in a few :P
 
It has nForce chipset, that is how you tell that it has SLI capabilities

There isn't any performance throttling or anything like that, Nvidia cards will work like they would on an Intel board, and the CPU will work like it would with an AMD chipset in there
 
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