There's never a bad time to use terms such as ‘teraflop computing power' and ‘dual GPU' if you ask me, so AMD's Radeon HD 3870 X2 is definitely off to a good start. Okay, the phrases might not actually mean much in the real world, per se, but they sure look good on a list of specs.
For those of you who missed the 3870 X2 leaks at CES I shall lay out the details for you. The card comprises of two 3870 cores bolted to one PCB and joined together electrically in a CrossFire configuration. That fact is noteworthy because it means that if CrossFire support isn't forthcoming for a game, the card isn't going to see the benefit of the second GPU.
The two-core combo is being referred to as RV680 and it is, as mentioned, two RV670 cores in tandem, which pack 825MHz clock speeds and are coupled to 1GB of GDDR4 memory running at 1.8GHz. AMD says this makes the chip faster than that on the standard 3870, and thus is citing the HD 3870 X2 as its fastest single-PCB solution, which on paper at least, it is.
Other features include PowerPlay, DirectX 10.1 support and AMD's Unified Video Decoder, as per the rest of the HD 3000-series. CrossFireX support is also intended to be added via driver updates, so in theory two X2s could be coupled in CrossFire, a la Quad SLI, although the phrase "diminishing returns" does spring to mind.
The card is available right now from various board partners and vendors, with pricing in the £300 range. As two 3870s will set you back around the £130-150 price range each the pricing doesn't sound too bad if you're playing games where CrossFire provides a worthwhile boost. Otherwise you're probably still better off spending your money on a single HD 3870, or an nVidia 8800 GTX or Ultra.