# 2 PCI-E x16 but not really???



## MrBucket (Oct 21, 2008)

Alright this might be a really dumb question but i was lookin at some motherboards and saw this and was wondering how crossfire would work on it:
*Expansion Slots*
PCI Express 2.0 x16 	2 x PCI Express 2.0 x16 slots (green @ x16 mode, blue @ x8 mode)
PCI Express x1 	1
PCI Slots 	3

I must be missing something because how can theyre be 2 PCI-E x16 but only one is at x8?

:EDIT:
Oh ya i was lookin at this board if it helps any
http://www.newegg.com/Product/Product.aspx?Item=N82E16813157141


----------



## netrick (Oct 21, 2008)

I am convinced the PCI-E people try to be as confusing as possible. My guess is they are saying it has two slots capable of running two PCI Express 2.0 x16 type graphics cards. The second slot will step it down to X8 though. So basically they are saying, yes you can use a X16 graphics card in this slot, but it will only run at X8. I know there are some boards like mine that have both slots at X16.

I'm not an expert on this either, so maybe someone else here can correct me if I am wrong, or explain this a bit better.


----------



## StrangleHold (Oct 21, 2008)

MrBucket said:


> Alright this might be a really dumb question but i was lookin at some motherboards and saw this and was wondering how crossfire would work on it:
> *Expansion Slots*
> PCI Express 2.0 x16 2 x PCI Express 2.0 x16 slots (green @ x16 mode, blue @ x8 mode)
> PCI Express x1 1
> ...


 

The 790X and GX doesnt have enough PCIe lanes to run both in X16. To have 2 PCIe X16 in crossfire you have to get the 790FX chipset. The 790GX is just a 790X chipset with onboard video.

Same with nvidia SLI with the 750a and 780a.

Its got to do with how many PCIe lanes the chipset supports.


----------



## 63083 (Oct 22, 2008)

I think what it means is that when you have two separate graphics cards, each will independanty run at 16X but when you enable crossfire, the second slot will step down to 8X. And no this will give a BARELY noticable performance hit. maybe a few fames. But no big deal. unless you like to get max fames.


----------



## StrangleHold (Oct 22, 2008)

63083 said:


> I think what it means is that when you have two separate graphics cards, each will independanty run at 16X but when you enable crossfire, the second slot will step down to 8X.


 
Depends on how they wired the board. Some boards have the 2 slots wired with 16 lanes. If both are wired for 16 lanes a (one) card will run with 16 lanes in either slot, but if you install 2 cards the second slot will auto drop to 8 lanes, so the second card will run with 8 lanes if its in SLI or crossfire or not.

Some boards have the second slot only wired for 8 lanes, even without a card in the first slot the second will only run 8 lanes.


----------



## 63083 (Oct 22, 2008)

I'm new with AMD but that's usually the case with Intel boards.


----------



## StrangleHold (Oct 22, 2008)

Makes no difference if its a Intel or AMD board. It all comes down to the amount of PCIe lanes the chipset supports.


----------

