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can a 6870 & 6850 be crossfired? - Page 2

post #11 of 29
Quote:
Originally Posted by 4LC4PON3 View Post



That is understandable & I agree I would like to have a single card setup but the 6850 was free so I may as well use it for now. I will plan on getting a 7950/7970 but not yet at least for a month. I have alot of funds right now going out on my new PSP Vita & getting a new car in a week or so plus a Disney Cruise.

For now I am sure it will be fine. Its better then running a single 6870 its free performance


hecks yea. free=free.

Enjoy the 70% performance boost! Crank those settings up!
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post #12 of 29
Quote:
Originally Posted by LA_Kings_Fan View Post

Pretty much ... each card does it's own thing ... so it will run just slightly better than x2 6850's, but not quite as good as x2 6870's, so whatever that translates out to ...


 



 


The 6870 will down lock. 6000 series have some of the best crossfire performance of any series
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post #13 of 29
I'm currently running a 6870 + 6850. It works very well. It's essentially the same performance as having two 6850's.

I've watched the GPU usage during benchmarks. The 6850 sticks at around 96% usage, while the 6870 fluctuates around 80% usage.

So you're not getting the full potential out of the 6870 obviously. But you can get some of that back by overclocking the 6850. No point in overclocking the 6870 in such a config, because it is bottlenecked by the slower card.

The benefit of having one card faster than the other is in games that do not support Crossfire. Configure the faster card as your primary card, and it will run at full speed when Crossfire is not in use.
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post #14 of 29
Quote:
Originally Posted by FlyingNugget View Post

The 6870 will down clock. 6000 series have some of the best crossfire performance of any series

Not true, both cards run at their standard clock speed. The faster card will just not be fully utilized.
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post #15 of 29

As mentioned ... wrong ... it doesn't DOWN-clock
 

Quote:
Originally Posted by FlyingNugget View Post
The 6870 will down clock.

 

Quote:
Originally Posted by wedge View Post
Not true, both cards run at their standard clock speed. The faster card will just not be fully utilized.


Well here's what happens ...  CrossfireX uses Scissoring / Super Tiling / and Alternate Frame Rendering modes to provide what is know as DYNAMIC LOAD BALANCING ... basically if a faster card is paired with a slower card the system won't divide the work load into equal parts the faster card renders a larger portion of the screen than the slower one thus having both cards finish at the same time. Ken1649 did a decent little example of how it kind of works here  ...

 

Quote:
Originally Posted by Ken1649 View Post

This example is exaggerated and over simplified with 100% perfect scaling;

 

6970 1536 shaders = Card A is faster clock per clock

6950 1408 shaders = Card B

 

In Crossfire;

 

Card A renders Frame #1 = 3ms

Card B renders Frame #2 = 4ms

Card A renders Frame #3 = 3ms

Card B .......

 

6970 + 6950 crossfire produces 2 frames/ 3.5ms

6970 + 6970 crossfire produces 2 frames/ 3.0ms

6950 + 6950 crossfire produces 2 frames/ 4.0ms

 



 

   
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post #16 of 29
Overclock them or atleast the 6850 to match the same pixel/texture rate as the 6870.
That would give you a nice performance boost.

My 2 6850s at 1010core/1150mem are faster then my single 7970 in BF3 ultra 4X aa at 1080 and lower res. At higher res the 7970 pulls ahead and since the latest patch they are very close at 1080 where there was 10fps before it.
post #17 of 29
Yes you can Crossfire these together, and if I am correct the 6870 will downclock to match that of the 6850.
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post #18 of 29
Quote:
Originally Posted by LA_Kings_Fan View Post

As mentioned ... wrong ... it doesn't DOWN-clock

 


Well here's what happens ...  CrossfireX uses Scissoring / Super Tiling / and Alternate Frame Rendering modes to provide what is know as DYNAMIC LOAD BALANCING ... basically if a faster card is paired with a slower card the system won't divide the work load into equal parts the faster card renders a larger portion of the screen than the slower one thus having both cards finish at the same time. Ken1649 did a decent little example of how it kind of works here  ...




 

That's a pretty good and accurate explanation. +rep
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post #19 of 29
Quote:
Originally Posted by LA_Kings_Fan View Post

Well here's what happens ...  CrossfireX uses Scissoring / Super Tiling / and Alternate Frame Rendering modes to provide what is know as DYNAMIC LOAD BALANCING ... basically if a faster card is paired with a slower card the system won't divide the work load into equal parts the faster card renders a larger portion of the screen than the slower one thus having both cards finish at the same time. Ken1649 did a decent little example of how it kind of works here  ...

I'm not sure about that. It is far too difficult to predict how long each frame would take to render on each card (Edit: That's the reason why micro-stuttering occurs even on two of the same card). Which would mean that the load cannot be dynamically distributed.
My own observations verify this to be true. The slower card is fully utilized, and the faster card is about 10 - 15% less utilized. Which means the work is being divided evenly, and the faster card is left "idle" for part of the time. If the work was being load balanced, then both cards would be fully utilized.
Edited by wedge - 2/17/12 at 3:09pm
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post #20 of 29
Thread Starter 
Thanks kings and everyone much appreciated. Some awesome info here
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