To be able to use two GPUs with the Stream SDK, we need to disable crossfire. But the 4870X2 is a specially wired card, which is why Catalyst does not allow disabling of crossfire. If there are two 4870X2s in a system, Catalyst should show the Crossfire option for those two cards.
We haven't tested 4870X2 with the SDK -- it is not on our supported cards. We wouldn't be able to use both the GPUs in that card until crossfire is disabled; the team is currently discussing the this feature.
Please let us know (or PM me) how and what project you plan to use the X2 for -- that will help in our prioritization.
I say this with a bit of hesitation (I have not tried the X2 myself) -- if you want to give it another shot, try on another OS, say XP32.
I'm planning to buy two 4870X2'a and I was also wondering how to disable Crossfire.
I understood Mike Houston implied on the Beyond3D forums that it's possible to use the X2's as two separate GPU's with CAL/Brook (just that the current Folding@Home GPU client fails to regognize them).
If you disable Crossfire with a dual card setup, would it also disable the "internal" Crossfire with the X2's? That's how it would work with Nvidia's Quad SLI.
BTW, I also have dual E5420's
Speaking for myself, I haven't decided purchasing 4870X2 yet - I'm waiting for CAL SDK being able to fully utlilize it.
I would like to see it running on 64-bit Linux (Ubuntu preferred) and exposing full 2GB of its RAM (not 1GB mirrored as in Cross Fire mode). I would accept that I'll see it as two independent devices with 1GB RAM each as I'll take care about load balancing myself - granted that I'll be able to see all devices from a single client process, including other cards plugged in (I'm not sure how it will work via X, so that's why I'm asserting it).
I have a similar problem too. But it's not HD4870X2, it's HD3870.
Previously, it was running fine with Cat 8.6, Windows XP x64 SP2, and CAL 1.1.
After I upgraded it to Cat 8.8 and CAL 1.2, the number of CAL devices reported became zero.
Running several prebuilt CAL 1.2 samples result in crashes.
Now I have to roll back to CAL 1.1