A little confused!

Gregry254

Gregry254

Gregry254

Associate
Joined
5 Dec 2006
Posts
607
Location
Aberdeen
I was under the impression than when you cross fire 2 ATI cards that both PCI-E slots would run at 16x?

But all the boards I can see run each slot at 8x when there is a second card in.

I presume that running two cards at half speed would be equal to having 1 card at full speed? so in the future when I upgrade I would see no difference from an extra card?

Either way could you reccomend a good motherboard for my build?

I plan on getting a i5 2500k, 8gb of 1600mhz ram, a HD6950 and an SSD.
 
If you go with your planned build with this mobo you will have the beginnings of a nice setup. Don't forget you will need a good psu if you decide to go sli/xfire.
Post back if you need help or suggestions with build... there's a lot of people here who will help !!
 
Gregry254 said:
So do all boards run at 8x when there is 2 or more cards in there then?

And if it does, how can 2 cards at 8x beat one at 16x?
Click to expand...

Because even with just one card there is generally no performance difference between 8x and 16x anyway.
 
It's not the speed of the cards that's halved it's the bandwidth of the slot.

A PCI-E 2.0 slot at x16 has a bandwidth of 8GB/s.

A PCI-E 2.0 slot at x8 has a bandwidth of 4GB/s.

As long as the graphics card doesn't exceed a requirement of 4GB/s bandwidth (and from the benchmarks no single GPU does) then it doesn't matter if it's in a x8 or x16 speed slot.
 
[H] hardocp August 23, 2010 gtx 480 sli performance tests conclusion said...

If you are running on a 30" display at 2560x1600 or below, an x8/x8 SLI or CFX configuration will perform the same as a x16/x8 or x16/x16 configuration. The only time that you should even be slightly concerned about running at x8/x8 is when you move up to a multiple display setup. When we pushed the GTX 480 SLI at 5760x1200 we saw up to a 7% difference in performance between x8/x8 and x16/x16, in favor of x16/x16, but that was in one game only.

t also appears that the type of game will impact the result and if there are even any differences at all. In texture and AA bandwidth heavy games, you will see more of a difference, but in a game that is more pixel shader heavy, there will be less or no differences at all.

If you are absolutely concerned about the best tradeoff, a middle ground so to speak, then x16/x8 is an excellent option. As we were discussing in last week’s evaluation, moving one video card to your x8 slot to create better airflow will not harm your gaming performance. However, downgrading your primary video card to x8 operation, in a multiple display configuration, can hurt performance at large resolutions.

When all is said and done, PCIe bandwidth isn’t as big of a concern as some people would like to make it. There are certainly many other factors that affect gaming performance more than PCIe bandwidth. It is clear that x16/x16, x16/x18, and even x8/x8 is plenty of PCIe bandwidth for today’s games. If you were wanting to save some cash on the motherboard and RAM you are using for a SLI or CFX system, it is hard to sit here and tell you that a x8/x8 setup is a "bad" configuration, even with a triple display Eyefinity or NV Surround. The x8/x8 SLI and CFX performance is going to be great at 2560x1600 and extremely good even at 5760x1200, but just keep in mind that you will sometimes be leaving a little bit of frame rate on the table at 5760. If you can live with that, you can keep some of that cash in your pocket and build the ultimate "budget" gaming rig.

HARDOCP - Conclusion - GTX 480 SLI PCIe Bandwidth Perf. - x16/x16 vs. x8/x8
 
You must log in or register to reply here.
Back
Top Bottom