I am preparing to buy a new GPU. Currenlty I am most inclined to buy a used HD4870 X2. However, on one of auction descriptions I found that on this card two GPUs are "crossfired" together. How does it relate to r600 driver, which has no support of CrossFire? Is the card seen by OS as a single or two GPUs? My understanding is, if OS is booted with two GPUs, it utilizes only one of them.
X2 cards show up as two GPUs on the PCI bus. Currently the open source driver is not able to utilize both chips in a crossfire configuration, but it will load on both GPUs and in theory you can use them independently, however, only one GPU has displays wired to it.
Considering I will not have any opportunity to benefit from two separate GPUs, like 3D modelling, I am better off with a cheaper, single card. I also considered HD 5870, but those are too expensive yet. And I am not going to buy anything else then the most powerful card of a generation. Now I am aiming for a cheap, but powerful one (it has twice as much flops as my current one, and much better driver support), and then I will be able to save up for the next generation card.