what is x8 mode?

[cCheeseCake]

I'm buying a motherboard and i need 2 pcie 2.0 x16 slots. The one i'm thinking of purcheasing has 2 pcie 2.0 x16 slots, but it say one of them is in x8 mode. What does this mean?

 

[jafrankl]

When using two PCI-e slots that are linked for SLI/Crossfire and they each run at x16 typically, they both go down to x8 speed when both are used. The second slot labeled x8 may only operate at that speed regardless of multiple GPU configuration depending on the board.

 

[kanewolf]

It means the physical size is a x16, but there are only 8 lanes of PCI data being fed to that slot. One of the cards won't have as much access to the system. Even with graphics cards, that penalty is only a few % ...