need some clarification on xfire

[darckhart]

hi i did some browsing and found bits and pieces but never a complete answers, so here goes:

1. just to confirm, i know xfire limits you to your "weakest" card. so if i have 2x 5850 and each are oc'ed and, we assume final clocks are different, it still takes the lowest stable one?

2. are CF profiles "generic" as in the profiles arent tweaked for 5850CF vs 5870CF?

and another question, since i can't really find this info, what's the performance difference i can expect between 5850 CF (moderate oc) vs 5870 (high oc)? hm at both 1920 and 2560 ultra super highest settings.

TIA!

 

[Sylvanas]

hi i did some browsing and found bits and pieces but never a complete answers, so here goes:

1. just to confirm, i know xfire limits you to your "weakest" card. so if i have 2x 5850 and each are oc'ed and, we assume final clocks are different, it still takes the lowest stable one?

2. are CF profiles "generic" as in the profiles arent tweaked for 5850CF vs 5870CF?

and another question, since i can't really find this info, what's the performance difference i can expect between 5850 CF (moderate oc) vs 5870 (high oc)? hm at both 1920 and 2560 ultra super highest settings.

TIA!

1. With two cards that are physically the same but with different clocks, they will both run at their intended core/memory frequency. So if card #1 runs at 800mhz by default and card #2 at 820mhz by default, card #2 will not down clock to 800mhz and both will run, mismatched at their respective frequency. Its been like this since Catalyst 8.1.

The idea that one card gets 'limited' by another perhaps get mixed up with the fact that if you have two cards with different memory sizes e.g. card #1 512mb and card #2 256mb, then the lowest common denominator will be used. In this case, both cards will use a 256mb framebuffer and the extra memory available on card #1 will not be used at all.

2. Yes, when ATI/Nvidia add a CF/SLI profile it is generic and applies to all cards multi-GPU configurations regardless of spec. So there won't be one profile for Crossfire 4670's and another for Crossfire 5870s. A 'profile' is essentially and application specific entry in the driver that enables the application to make use of the resources of more than 1 graphics card in a Crossfire/SLI setup.

3. Two 5850s will deliver higher framerates than a single 5870 regardless of how much either is overclocked. Of course the 5870 is the simpler and more linear solution.

 

[darckhart]

oh great! thanks for info. and what happens if you pair mismatched cards like 5850 + 5870? does the 5870 not use its extra simds?