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Considering the CrossFireX possibilities
The Radeon HD 4870 X2 comes with a single CrossFire bridge connector, which opens up some intriguing possibilities. The most obvious of those is the potential of harnessing two X2 cards together for quad-GPU mayhem. We've done it, of course. Another possibility is hooking the 4870 X2 together with a card like this one...

Diamond's Radeon HD 4870

Diamond was incredibly kind to provide this Radeon HD 4870 card for our use in multi-GPU testing, and we've done exactly that. This is a single-GPU card with 512MB of GDDR5 memory, my current favorite graphics card value. The X2 can team up with it to achieve a three-way CrossFireX config. You do end up compromising on total memory when you go this route, however, because the CrossFire gods demand symmetry. AMD's drivers will treat each GPU in the team as if it has 512MB of memory attached to it, since that's the lowest common denominator. We'll see whether (and how much) that hurts when we get to our performance results.

New GeForces, newer prices
The 4870 X2's main competition, duh, comes from Nvidia' GeForce GTX 200-series lineup. That's elementary, but we do need to recalibrate our expectations somewhat in light of the impressive downward movement of GeForce GTX prices since the cards' introductions. Let's have a look at cards we used for testing as examples.

Like our 4870 X2, many of the GeForce GTX 260 and 280 cards we used in testing came from Palit, who seems to be everywhere lately. They were kind enough to provide us with a big chunk of the cards we used for this article. The two cards pictured above actually are different products, although telling them apart isn't easy. The one on the right is a GeForce GTX 280, and that card is currently selling for $429.99 at Newegg, along with a (boo! hiss!) mail-in rebate that will, if and when you receive the funds, will take the net price down to 400 bucks. That's a long, long way from the $649 introductory price. On the left in the picture above is a GeForce GTX 260, currently listing for $289.99 at Newegg and $269.99 after rebate. Again, quite the drop from its $399 debut.

In light of these prices, Nvidia claims the most appropriate competition for the Radeon HD 4870 X2 would be a pair of GeForce GTX 260 cards in SLI. That does make some sense, but remember that running a couple of GTX 260 cards in SLI imposes some strict requirements. Most notably, you'll need to have a motherboard based on an nForce chipset, because Nvidia has restricted SLI to its own core logic. On top of that, the GTX 260 SLI config will chew up two PCIe x16 slots and (including coolers) a total of four expansion slots inside of your PC, and it will require twice as many PCIe power leads as the 4870 X2. And don't get me started on multi-monitor support. Let's just say AMD supports dual monitors reasonably well with the X2 and other CrossFire implementations, while SLI requires the user to engage in a manual mode-switching ritual before launching a game.