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I just added another HD 4890 to my current setup to run the two in crossfire.

If I now want to overclock them via Catalyst, do I need to tweak the clocks on both the cards manually, or can I synchronize them in such a way that increasing one clock makes the same increase on the other too?

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if you need to ask, you don't need to be doing this –  hbdgaf Nov 22 '10 at 15:15
    
wow...geez. thank you. That was helpful. I've been overclocking for years. My HD 4890 was running at 1Ghz, my processor (AMD Phenom II x4 965 BE is liquid cooled and run at 4Ghz (up from 3.4..I could safely push it more if I used a 32-bit OS), and I have my RAM GSkill Ripjaws underclocked from 2000Mhz to 1600 so I could tighten the timings. I have more than ample experience with overclocking. Its just my first time using a dual GPU setup. –  xbonez Nov 22 '10 at 15:33
    
fyi: i know that in a crossfire setup, both GPUs need to be operating at the same clocks. I was just wondering if there's a way I could synchronize both clocks to reduce my work (changing both clocks one at a time) and reduce the chance of human error. –  xbonez Nov 22 '10 at 15:42
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1 Answer

up vote 2 down vote accepted

You can technically clock each one differently in ATI Catalyst Control center using the "Select GPU to configure" drop-down here:

enter image description here

I know for a fact that clock differences aren't a dealbreaker in Crossfire because my two 5870s have slightly different clocks (850 vs 875) and it works fine.

However, the nature of the work (either rendering fragments of the screen, or alternating frames of the screen) means that synchronized clocks are best. I'm planning to down-clock both cards to the same 850 Mhz.

I personally would be very very hesitant to overclock a Crossfire rig at all, as they are already more complex, generate tons more heat, etc.

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