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Help out a CrossFire newbie.

B

bustaplz

Limp Gawd
Joined
Oct 26, 2007
Messages
130
I recently picked up a Sapphire 5870 1GB used for $200 to run CF with my HIS 5870 1GB. The strain of 5760x1080 was a bit too much for the one card.

I have a few different questions about CF, as I have never run a multi-GPU setup.

I had my HIS card OC'd to 915/1300(highest stable OC) and ran the Arkham Asylum benchmark before trying to install the second card just to have something to compare to. I wrote down 53 fps average. After several reboots and failed attempts at installing the second card I figured out that MSI Afterburner was set to 'sync' settings across my GPUs.

Obviously, I didn't know if the Sapphire would run at those clock speeds, so I pulled the HIS card out and booted up with just the Sapphire, installed the drivers. I tried to OC the card, but was limited to only 900MHz Core Clock from the standard 850(I think) and I can't remember every having this issue with my HIS. I came across a little hack to let Afterburner go past these clocks, but I didn't really feel comfortable with it since I don't understand the limitation.

I overclocked the memory to 1250MHz, determined it stable and ran the benchmark again. 49 average fps.

So, the question part:

1. Is there a reason this new card doesn't want to let me try out higher clocks?
2. What is the generally accept method of installing a second card for CrossFire, in terms of drivers, bridges, whatever.
 
Generally speaking Crossfire is more sensitive to overclocking. AFAIK they both have to be the same clock speed, GPU and RAM, across both cards. Don't expect to be able to OC like you can with one card. I know I have the same issue with my 4890's, both of which are stock OC'd and will not run more than a few Mhz out of spec in Crossfire.

There isn't any special method for installing Crossfire AFAIK. I certainly didn't do anything special.
 
I'm a bit unclear as to what your issue is. Are you saying that you're unable to clock the 2nd card to match the first due to it being unstable, or is it because you're running into an artificial limitation (like the slider just won't go past 900, etc)?

There should be no issues with crossfire even if both cards have mismatched clocks. Both of my 4870x2 cards are pre-overclocked models but at different pre-overclocked speeds. Everything works fine even with the mismatched clocks but I was able to clock the slower card to match the faster card anyway.

IMO if you're running into stability issues, just clock them both at 900/1250 or whatever and call it a day. You're crossfire performance will still crush your single-card performance.
 
Even with both cards at stock clocks, you'll see major gains over a single overclocked card. Personally, I would keep the cards at their stock clocks.

There's not much more to crossfire other than installing 1 bridge (you only need 1 even though the cards have 2 connector tabs, thats for 3x or 4x crossfire), and enabling it in CCC. Other than that you should be good to go.
 
Thanks for the tips, guys!

Unfortuneately, I haven't been able to give it another try as I seem to have murdered my CPU. Amazon says my 970 will be here tomorrow, but it still hasn't shipped out.

I'll post back if I still can't figure it out.
 
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