xfire @ x16 x4?

[aceofspadesrob]

why are most if all p67 xfire boards 16x and 4x when in xfire and what proformance would you lose over 8x8 bandwith?

currently have a asus p8p67 LE mobo and 1 6950 want to xfire but if i want it to be worth while do i need a better mobo? thanks for answers lads and lasses(like there are any women on here XD)

 

[Surveyor]

There are a lot of P67 boards which run at x8/x8.

This gives you some idea of x4 performance:

GTX 480 SLI PCIe Bandwidth Perf. - x16/x16 vs. x4/x4

If you plan on using the second x16 slot (x4 speed) for Crossfire you'll need to disable the x1 PCI-E slots as they share bandwidth.

 

[aceofspadesrob]

informative post and cleared things up thanks, how would i disable the pcie x1 lanes ? bois setting?

 

[Surveyor]

Onboard Devices Configuration in the BIOS.

Change "PCI Express X16_2 slot (black) bandwidth" from Auto to x4.

Just to balance it up I've found another test which paints a less rosey picture:

PCIe Scaling Summary

In that test AMD/ATI cards are affected worse than Nvidia.

And in this test at x16/x4 some games are hardly affected and some suffer a big reduction compared to x8/x8:

Bonus Page: Does CrossFire Work At x16/x4?

 

[aceofspadesrob]

thanks v much i apreciate your time

 

[Surveyor]

thanks v much i apreciate your time

You're welcome.

It looks like x16/x4 is very hit and miss depending on the game.

Best case scenario it's almost as good as 2 HD 6950's at x8/x8.

Worst case scenario it's like running 1½ HD 6950's at x8/x8.

Possibly in the first test they just picked the right games or the Nvidia cards just worked better.