When AMD's ATI Radeon HD 4870 (or RV770 if you prefer) launched we all knew something bigger and better was coming. Well, as of today that product is here and it is, in fact, two products, both falling under the R700 banner, named the ATI Radeon HD 4870 X2 and the ATI Radeon HD 4850 X2. Both take a leaf out of the ATI Radeon HD 3870 X2's book and packing two graphics cards into one package. Because we all know two heads graphics cards are better than one!
Specs and pricing for the new cards sit as follows:
Whereas the AMD ATI Radeon HD 3870 X2 boasted 6.8GB/sec of inter-card communication, the 4870 X2 offers 21.8GB/sec. This is in part from the move to PCI Express 2.0 (which has twice the bandwidth of the first generation) and the addition of another 10GB/s (5GB/s each way) interconnect between the two GPUs. That's actually a fairly important factor in making the multi-card set-up scalable, as performance bottlenecks occur when the cards can't talk to each other quickly enough.
On paper, AMD says the HD 4870 X2 and 4850 X2 should be 'up to' 1.8 times faster than a single HD 4870/4850. Apparently that level of scalability continues when adding yet another X2 to the mix, for four-way CrossfireX, with most games exhibiting 1.6 to 1.8 times the performance of a single X2. Future driver updates should ensure that improves, as well as ensuring upcoming games see similar benefits.
That means both cards more than enough power to trounce the GeForce GTX 280, nVidia's fastest offering. Depending on your definition of a 'single card' graphics card nVidia might arguably still have the fastest, but given the price points AMD is hitting, consumers probably won't care to much for semantic arguments.
Given the power-draw and size of the GTX 280, it seems unlikely that nVidia will be launching a dual-GPU card any time soon, although I'm quite prepared to be proved wrong. It's been a while, but AMD is finally getting back on top of the graphics game.