Crossfire on cheap 775 board?

[qkhanhpro]

So, As i know there's almost no noticeable difference between x16-x4 VS x8-x8 Crossfire. But, I really wonder if there'll be any difference CF with 775 and 1155 board and between cheap and expensive board?

 

[Durvelle27]

actually there's a big difference between x16 and x4 vs x8 and x8 ?

 

[GotNoRice]

It's been shown numerous times that even with PCIe 2.0, that 4x is not a significant bottleneck for Multi-GPU. The faster the cards you are considering using in crossfire the more potential bottleneck there would be, but I'm guessing you're not talking about something like 7970 crossfire if you're looking at a "cheap 775 board".

What cards are you looking at using? What motherboard?

 

[qkhanhpro]

Maybe Asus P5K or smt ~50$ second hand with 2 x 6870
Is it fine?
Thanks

 

[GotNoRice]

Maybe Asus P5K or smt ~50$ second hand with 2 x 6870
Is it fine?
Thanks

Well the P5K uses the P35 chipset. It will still work in Crossfire, but it is a PCIe 1.1 board instead of PCIe 2.0. That means the 4x slot on that board will be even more limiting, the equivalent of a 2x PCIe 2.0 slot, or a 1x PCIe 3.0 slot!

With something like a pair of 6870s, you will probably be okay, but I'd still expect to see a penalty upwards of 15% due to bandwidth limitations. If you can find a board with PCIe 2.0 slots, you could reduce that limitation to more like 5% probably.