For 4870 Crossfire X48 or P45 motherboard

[9nines]

The new Intel P45 chipset motherboards have PCI-e 2.0 X16 if you use only one card but if you go Crossfire it gives 8X bandwidth to each card. Will that be limiting? Or will the cards not use more than 8X in each slot? I am trying to decide whether I should get an X48 chipset motherboard, which I think does 16X in each slot, instead.

 

[ghost recon88]

The 8x will limit the cards, get an X48.

 

[Jax Omen]

PCI-E 2.0 x8 is equivalent to PCI-E 1.0 x16, which hasn't bottlenecked a GPU yet in anything other than Flight Simulator X.

P45 is absolutely fine. Get whichever board fits your budget.

 

[9nines]

Actually I found a test site that shows the X48 to outperform in Crossfire by large margin:

Here is the article incase anyone else is wondering: http://www.tweaktown.com/artic...ntroduction/index.html

 

[Jax Omen]

That is honestly fascinating. I've never seen anything indicate a difference between 8/8 SLI and 16/16 SLI, but that clearly indicates a difference between 8/8 crossfire and 16/16 crossfire.

I wonder what ATI does differently that causes this?

 

[9nines]

Also, this begs the question: Would two Crossfire cards perform better than similar X2 cards? In other words, would two 4870s on X48 MB perform better than the future 4870X2. The 4870X2 would only have one X16 channel for both GPUs, whereas the Crossfired 4870s would each have 16X, right? So according to the article's results, one could assume that the 4870X2 might be bottledneck, even if the two GPUs bridge better.

 

[Sylvanas]

Originally posted by: 9nines
Also, this begs the question: Would two Crossfire cards perform better than similar X2 cards? In other words, would two 4870s on X48 MB perform better than the future 4870X2. The 4870X2 would only have one X16 channel for both GPUs, whereas the Crossfired 4870s would each have 16X, right? So according to the article's results, one could assume that the 4870X2 might be bottledneck, even if the two GPUs bridge better.

Well it depends how much bandwidth those two GPU's are going to use. PCI-E 2.0 16x is 8gb/s opposed to PCI-E 16 1.1 (or 8x 2.0) being 4gb/s. If the 4870X2 requires only say 5GB's then theres still plenty of headroom there in which case it'll be fine, which is what I would imagine. ATI are not going to release a card that is Dual GPU and limited by a PCI-E 2.0 slot, one things for sure, I am glad I jumped on the 2.0 bandwagon early in anticipation for this.

If you can wait, rumour has it that the 4870X2 will not simply be a remake of what the 3870X2 was, it will have a new form of Inter-GPU communication over the memory bus (not the PLX chip from before) which increases Crossfire scaling and also eliminates the so called 'microstutter' inherent in all SLI/CF configs (only some people can notice it- I haven't). So in that situation the 4870X2 would be better over 2x 4870.

 

[9nines]

Originally posted by: 9nines
Actually I found a test site that shows the X48 to outperform in Crossfire by large margin:

Here is the article incase anyone else is wondering: http://www.tweaktown.com/artic...ntroduction/index.html

Maybe instead of the 16X/16X versus 8X/8X being the explanation for why the X48 motherboards have higher FPS, it is the memory speed difference between the X48 & P45. For example: read this article that is just trying to highlight CPU & memory utilization difference between the chipsets:


http://www.hothardware.com/Art...pset_with_DDR2/?page=7

Remember those lower peak memory bandwidth and higher latency scores in the SiSoft SANDRA benchmarks? Well, here's where they've appeared to have an affect. In both the Crysis and F.E.A.R. low-resolution tests, the P45 based Asus P5Q Deluxe finished behind its X48-based counterparts, to the tune of 6% to 10%. We suspect there is still some BIOS tuning work to do, to get the P45's performance up here a bit.