CrossfireX @ PCIE 2.0 X4 speed, Is this fast enough?

[rapsux321]

Hi, looking at the ASUS M4A78 Plus AM3/AM2+/AM2 AMD 770 ATX AMD Motherboard, I noticed the when in Crossfire the 2 slots being used run at PCIE 2.0 X4. Normally these run at least at 8x, and on better boards at the standard 16x. Most of the time 16x is overkill correct? 8x is probably more than adequate in most scenarios, but 4x seems a little sketchy. Anyone have experience or data that would say crossfire @ 4X is not enough bandwidth for video cards? or what card model would the cutoff occur at? Thanks!

 

[megamanx00]

Even toms has some articles covering PCI-E bandwidth affecting cards. Generally 4x is pretty low and will give a performance drop for a single card. As for crossfire it's best to have the slots using the same number of lanes. Mixing lanes, like a 16x and a 4x, limits performance and sometimes can actually lead to lower performance than just using a single card. Anyway you may want to check out this article on legion hardware to compare different crossfire setups

http://www.legionhardware.com/document.php?id=761

Anyway for modern cards you really should use at least two 8x slots. Of course two 16x PCi-E 2.0 slots is ideal, but they really only have a significant advantage over two 8x slots when using something more powerful than a 4850. It is pronounced when using dual GPU cards for 4way crossfire like the 4850x2 and 4870x2