Crossfire question!

[Necc]

Hey there!

So Irecived my bouns today and was thinking on buying another 5870 and crossfire it with my exsisting one, but Inoticed that my mobo has a 2nd pci-e that is only 4x, so iguess if i'd go crossfire then both cards will work in 4x/4x mode, should i even bother? will isee performance increase working at 4x? Ihave a very good vantilated case, with an HX850 psu so power/heat shouldnt be a problem.

Thanks.

 

[dma0991]

If your second PCIE slot is 4x then your Crossfire would run at 16x4x. The problem is that there is more performance drop with a 16x4x rather than the ideal 8x8x or 16x16x motherboards. The performance drop from 16x16x to 8x8x is minimal unlike 16x4x.

Also the scaling on HD5000 series cards are not as good as the HD6000 series card so would expect some drop from scaling issues as well. Your PSU supports both cards easily and if you're tight on budget and do not want to change your motherboard, just get another HD5870 and Crossfire it anyway.

 

[mhouck]

Necc, what resolution are you running at? and how much have you budgeted to the 2nd 5870? are you looking at the 2gb version?

 

[dakU7]

If your second PCIE slot is 4x then your Crossfire would run at 16x4x. The problem is that there is more performance drop with a 16x4x rather than the ideal 8x8x or 16x16x motherboards. The performance drop from 16x16x to 8x8x is minimal unlike 16x4x.

Also the scaling on HD5000 series cards are not as good as the HD6000 series card so would expect some drop from scaling issues as well. Your PSU supports both cards easily and if you're tight on budget and do not want to change your motherboard, just get another HD5870 and Crossfire it anyway.

Performance drop from 8X/8X is also minimal, he probably won't feel it.

http://www.hardocp.com/article/2010/08/25/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x4x4/

This is a worst case of X4/X4 and you can see it has almost no affect on performance compared to the x16/x16.

 

[Necc]

Necc, what resolution are you running at? and how much have you budgeted to the 2nd 5870? are you looking at the 2gb version?

Im running 3x19" monitors eyeinfinity 4320x900 but in the summer switching to an 30" dell U3011. Ican get a 2nd hand 1gb 5870 for 150 us dollars. ican get higher then that but tops ~250. but idont really want to change my mobo either.

Performance drop from 8X/8X is also minimal, he probably won't feel it.

http://www.hardocp.com/article/2010/08/25/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x4x4/

This is a worst case of X4/X4 and you can see it has almost no affect on performance compared to the x16/x16.

That would be awesome, but isnt SLI scalling better then crossfire? in the article they are testing gtx480's.

 

[SlowSpyder]

I can't say for sure, but I would think you'll get a nice boost at both those resolutions. I went CF and am quite happy with it. I play at 1920x1200, though. But I think for the money a second card would cost you'll get a quite good bang for the buck performance increase.

 

[Lepton87]

That would be awesome, but isnt SLI scalling better then crossfire? in the article they are testing gtx480's.

It's a bit better then 5000 series and a bit worse then 6000 series. I wonder why 6000 series scales better then the previous series. They didn't make any hardware changes that would explain that. I suspect that they artificially hold scaling back in 5000 series or don't bother to improve the drivers.

 

[Necc]

So Ishould go with the 2nd 5870 and call it a day? iwill see improvments as all you guys said if iwont I'll be back and hunt you down

Thanks again :thumbsup:

 

[Lepton87]

I added a second 5870 to my computer about two weeks ago and I'm very pleased with the results. Performance went up significantly. In a lot of workloads performance improved over 50% and its very noticeable. Having said that I still don't see a legit reason why performance scales worse than 6000 series.

 

[Cuular]

Because contrary to the average belief, the 6 series based on the VLIW4 has a lot of changes to it. It's not just an upgrade. It was a switch to a new underlying process. And the lower end 6 series based on the VLIW5 also had a lot of rework and updates done to it.