AMD Radeon HD 6990

I'll be blunt: the AMD Radeon HD 6990 is a beast. Soundly outpacing the best that Nvidia has to offer (at the moment), this dual-GPU juggernaut -- previously codenamed "Antilles" -- clambers to the top of our graphics card heap by serving up the most raw power we've seen to date. But then there's the price: at $699 (as of 3/8/2011), it's strictly aimed at those ultra-enthusiasts who'll spare no expense on their gaming rig.

But rest assured, you're arguably getting your money's worth -- provided you're already living luxuriously on the bleeding edge. The Radeon HD 6990 is pricey, but it proved to be demonstrably faster than its closest competitor, the $500 Nvidia GeForce GTX 580. For comparison's sake, I also included the $350 AMD Radeon HD 6970 -- the company's recent single-GPU speed champ.

Inside a Juggernaut

The "Cayman" GPU debuted in AMD's 6900 series, in the aforementioned Radeon HD 6970 graphics card. The Radeon HD 6990 combines a pair of these GPUs onto a single card -- think Crossfire, on a stick. The end result is a powerful graphics card that fits comfortably into a single PCI slot (though the card is two slots wide), leaving plenty of room for a second...

In keeping with AMD tradition, the Radeon HD 6990 manages to eke out serious speed while sipping electricity. It's designed to meet a 300W TDP at its stock, factory settings -- that's relatively meager for such a beefy part. The card requires dual 8-pin connectors, so make sure your power supply is up to snuff before you grab your wallet.

The Radeon HD 6990 also offers up something special for customers who want to grind the most power out of their $700 bauble. A dual-BIOS switch on the side of the card toggles the part from its stock, factory-supported position to an overdrive mode, with increased clock speed and voltage demand. AMD calls it the "Antilles Unlocking Switch for Uber Mode," or AUSUM; I won't. Coupled with AMD's Power Tune application, you'll have a wide range of control over the GPU and Memory clocks. For these tests, I also compared the Radeon HD 6990 at its stock speeds (830 MHz), to it's base overclocked setting (880 MHz) -- referred to as Radeon HD 6990 OC for simplicity's sake.

Before we talk results, lets talk features. The Radeon HD 6990 offers five display outputs: four mini-display ports, and a dual-link DVI port. Every card will ship with 3 adapters (two mini-DisplayPort to DVI, and one mini-DisplayPort to HDMI), for use in an Eyefinity setup. You can drive up to six displays from the card, including arranging five 24-inch screens in portrait mode. Or my personal favorite: driving three 30-inch monitors. If you happen to own, or are considering purchasing three 30-inch displays, a $700 graphics card is likely pocket change (and if you happen to be looking for a roomate, I'm available).

Crunching the Numbers

On to the numbers! Our testbed consisted of a Core i7-2600 processor, running at its stock 3.4GHz clock speed, 4GB of RAM, and Windows 7 Home Premium (64-bit). The latest drivers were used for both cards -- in AMD's case, it was a preview version of their Catalyst 11.4 driver.

As always, we'll start with the synthetic benchmarks. First up is Futuremark's 3DMark 11. It's the latest version of the tried and true 3DMark benchmark suite, though 3DMark 11 has been designed for the DirectX 11 era. The benchmark churns through a number of graphics and CPU intensive tests, and then assigns a score based on how the hardware performs.

The numbers speak for themselves. The Radeon HD 6990 boasts a 67% lead over the Nvidia GTX 580 on the Performance setting, sliding up to 70% in Extreme mode.

The 3DMark 11 score includes CPU tests, so I went ahead and isolated the results for the GPU tests. That's an 89% lead over the GTX 580 on the Performance setting, and a 75% lead at the Extreme setting. In a word: Wow.

The tale is rather similar with our second synthetic test, Unigine's Heaven benchmark. Heaven is a rather forward looking benchmark, gorgeous and graphically intensive in equal measure. If you'd like to try it out for yourself, there's a free version available at Unigine's website. Performance is a bit closer here -- the GTX 580 comes within spitting distance of the 6990, just under 12 frames per second slower at the maximum resolution, 4x AA. The divide grows whenever anti-aliasing is shut off, but you probably aren't going to buy a $700 graphics card to scrimp on visual extras.

Real World Performance

Synthetic benchmarks are an accepted industry standard for checking out theoretical performance, but let's take a look at how the Radeon HD 6990 fares when tackling real games.

First up are our Dirt 2 and Far Cry 2 benchmarks. Both games are graphically intensive, sporting intricately lit dynamic environments and a fair bit of action. Both resolutions for both tests are run at highest quality settings, with 4x anti-aliasing. At the 1920-by-1200 setting, the results are fairly close. In Dirt 2, the Radeon HD 6990 offers a mere four extra frames over the GTX 580. That climbs up to 27 frames in Far Cry 2, but with the total being just shy of 120 frames per second, you aren't likely to notice the difference.

But if you're buying a $700 graphics card, you really ought to be playing on a larger display. At the 2560-by-1600 level of our benchmarks, the Radeon HD 6990 takes advantage of that 4GB of DDR5 memory to maintain a much stronger lead -- to the tune of 35% in Dirt 2 , and 64% in Far Cry 2 .

Our last two games tests are even more intensive. We'll start with S.T.A.L.K.E.R.: Call of Pripyat . With an emphasis on dynamic shadows and tessellation, it's the first test that manages to pull even the lofty Radeon HD 6990 into the double digits.

A result of 30 frames per second is generally considered playable. Both the GTX 580 and the Radeon HD 6970 manage to hit that mark at the highest level of our test, but if you're playing on a 30-inch display with all of the bells and whistles cranked up, the Radeon HD 6990 remains an overall smoother experience.

The same goes for Just Cause 2 , the most strenuous of our gaming tests.

In this case, the GTX 580 actually dips just under the playability line, and the Radeon HD 6970 is hanging on for dear life.

The Radeon HD 6990 tackles the title with aplomb, its twin GPUs managing to double the performance of Nvidia's offering.

There's a lot to consider when measuring the overall value and efficiency of the Radeon HD 6990. First, there's the dollars per frames per second measure, which I'm summarized in this handy chart (click on it, to see the full sized version). In a nutshell, this compares the price of each card to the average frames per second achieved in our games tests. I included the results of the Radeon HD 6990 in its overclocked mode, for good measure.

The overall winner from a pragmatic perspective is the $350 Radeon HD 6970. It doesn't offer up nearly as impressive performance as its pricier rivals, but it sits at a price that's a bit more cost-effective. At a 1920-by-1200 pixel resolution, the Nvidia GeForce GTX 580 is technically the better deal. But once you've cranked up the resolution to 2560-by-1600, the Radeon HD 6990 offers a strong price to performance ratio -- particularly when running at the overclocked BIOS setting mode.

Power, and Efficiency

Next, we'll take a look at power efficiency. This one is going to be a little counter intuitive: when under a full load, the Radeon HD 6990 used more power overall. But it generally did so more efficiently. To arrive at these figures, I divided the power used under load by the average results for our games tests. At the 1920-by-1200 resolution, the Radeon HD 6990 and the GTX 580 are pretty much neck and neck. They're both consuming substantially more power than the Radeon HD 6970, but they're generating plenty more frames as a result. The picture becomes much better when we crank the resolution up to 2560-by-1600 pixels. Here the Radeon HD 6990 is the clear winner, making the most of its power consumption.

That the Radeon HD 6990 manages to post such impressive results while sitting at about 300W is really impressive. Switching over to the overclocked BIOS mode is a bit less energy efficient, but that much is expected.

And there you have it, the world's fastest graphics card (for now). Truth be told, Nvidia will surely be prepping a dual-GPU response of its own, so even the well-heeled gamer shouldn't dive headlong just yet. Of course, therein lies the rub of living on the bleeding edge. The Radeon HD 6990 will cost you a pretty penny, but its money well spent -- if you're running multiple large displays or at least one 30-inch monitor, and have the hardware and software to take advantage of what the card has to offer. If this doesn't apply to you then by all means, check out the offerings further down on our Top Rated Graphics card chart. Both the AMD Radeon HD 6970 and the Nvidia GeForce GTX 570 offer an excellent gaming experience for we mere mortals.