AMD Radeon HD 6990

Let's get the obvious (and most-important) news out of the way first: The dual-GPU AMD Radeon HD 6990 is the fastest video card ever. If you are looking for the ultimate tool for improving and speeding your games' graphics, this is it. It trounces the competition, including its own illustrious predecessor, the ATI Radeon HD 5970, and delivers the kind of frame rates in DirectX 11 (DX11) titles we didn't think possible even a few months ago. Simply put, we adore this card's capabilities, and must award it our Editors' Choice. But—and this is a big but—it's not for everyone. Bearing a faint-worthy sticker price of $699 list, power bill–inflating electricity usage, and all the standard caveats associated with top-tier gaming cards, the Radeon HD 6990, part of AMD's new Antilles family of cards, is aimed squarely and only at wealthy, reckless, and frivolous gamers who believe that having the best (and biggest) hardware is its own reward.

Design and Features

There's no doubt about it: Everything about the 6990 is big, starting with its specs. It packs 5.1 teraflops of compute power. It has a core base clock speed of 830 MHz. It has 3,072 stream processors, 192 texture units, and 64 ROPs. It's got a frame buffer of 4GB of GDDR5 memory, operating on a 5-Gbps, 256-bit memory path.

In case all this isn't quite enough for you, it's possible to go just a little bit bigger. As with some other 6000-series cards, there's a dual-BIOS switch (located next to the I/O bracket) that lets you engage a built-in overclocking option. Flip it to increase the standard clock speed from 830 MHz to 880 MHz, and the voltage from 1.12 volts to 1.175 volts, for a new compute power level of 5.4 teraflops. This is a remarkably easy way to squeeze yet more performance out of the card, though as we'll see it doesn't come without some sacrifices.

The 6990 is also physically big. Like the 5970, it measures 12.5 inches in length, making it the longest card you can buy. Trying to house it in anything less than a full-tower case is taking a real chance, and we even hit a snag in our spacious Thermaltake Element V: We had to rearrange the hard drives to get the 6990 to fit, because the SATA data and power cables just stuck out a few millimeters too far. Like many other cards of this size, the 6990 also boasts a bulky heat sink and fan assembly, which means it will block a second expansion slot next to the PCI Express (PCIe) x16 slot you install it in. 

Big connectivity is possible, though this also represents a big departure for AMD. Outputs include one dual-link DVI port and four Mini DisplayPort jacks, letting you run Eyefinity setups with as many as five monitors at once. In case you're not exactly drowning in Mini DisplayPort–capable monitors, don't worry: All versions of the 6990 will ship with three adapters: one passive Mini DisplayPort–to–single-link DVI; one active Mini DisplayPort–to–single-link DVI; and one passive Mini DisplayPort–to–HDMI.

Then there's the question of the 6990's big power usage. We'll get into this more later, but you'll want a beefy power supply before you even consider installing this thing. And make sure that, via either your PSU's native connections or Y-cables, you have access to two eight-pin PCIe power adapters, because you'll need them. (This is a rarity—previous front-of-the-pack cards, like the 5970 or Nvidia's GeForce GTX 580, required one eight-pin connector and one six-pin connector—but understandable given the card's power demands.) AMD restricts the 6990's power usage to 375 watts in regular mode, and 450 watts when overclocked, with the typical average gaming draw at about 350 watts and 415 watts, respectively.

In all cases, that's a lot, and even if the board idles as claimed at 37 watts (in both standard and overclocked mode), excessive power draw is a real concern. A new technology AMD calls PowerTune is designed to help alleviate this, and let the 6990 operate safely beyond 300 watts. PowerTune dynamically adjusts the engine clock on the fly based on an ongoing assessment of the GPUs' power usage—this lets it run within its TDP budget at the highest-possible clock speeds. The Catalyst Control Center software gives the user some control over the power containment, in case they want to push the boundaries of performance further still.

All this additionally requires big design changes to deal with performance and heat dissipation issues. A new symmetrical design places each of the GPUs at opposite ends of the cards, with regulators in the center—according to AMD, this maximizes power delivery to the chips and their associated memory. A completely enclosed shroud, which contains dual vapor chambers and phase change thermal interface material, keeps the card cool.

Performance, Power Consumption, and Noise

Of course, the primary thing that anyone seriously considering the 6990 cares about (and should care about), is performance. And this card's, as we've said, is unparalleled. We hit it with our entire arsenal of DX11 benchmark tests—all at the highest typical resolutions (1,920 by 1,200 and 2,560 by 1,600), with the details maxed out—and the 6990 made mincemeat of them. It then proceeded to bake that mincemeat into pies and feed them to not just Nvidia's performance leader, the GTX 580 (we also tested Zotac's overclocked version), but also the 5970, earning across the board the best scores we've seen.

The 6990's numbers in the fresh and still-demanding 3DMark 11 were unbelievable: 8,901 using the Performance preset (1,280 by 720), and 3,285 using the Extreme preset (1,920 by 1,080). In Aliens vs. Predator, it nabbed 77.2 frames per second (fps) and 48.4 fps; in the Heaven Benchmark it slid to an easy and smooth 46.4 fps and 35.2 fps. Just Cause 2 saw 68.4 fps and 48.7 fps, Lost Planet 2 returned 51.5 fps and 42 fps, Metro 2033 came in at 54.3 fps and 35 fps, and S.T.A.L.K.E.R.: Call of Pripyat rang in at an impressive 91.2 fps and 61.5 fps.

All these numbers, by the way, are with the 6990's overclocking switch off. Flip it, and you see even better results: 9,175 and 3,419 in 3DMark 11; 79.9 fps and 50.5 fps in Aliens vs. Predator; 48.5 fps and 37 fps in the Heaven Benchmark; 70.2 fps and 50.6 fps in Just Cause 2; 53.4 fps and 43.6 fps in Lost Planet 2; and 94.5 fps and 64.3 fps in S.T.A.L.K.E.R. The only stumble here was in Metro 2033: The overclocked 6990 earned 52.7 fps at 1,920 by 1,200, not enough to beat the base clocking, and edged just barely over with 35.3 at 2,560 by 1,600. No, the overclocking won't blow out every title, and even if it's rather gentle at the AMD-recommended boosted speeds, it's still a noticeable improvement—for no more money. Is there anything the 6990 can't do?

Well, yes. The 6990's Antilles heel is its power consumption. Which is, as we've stated, excessive. Granted, this was to be expected given its dual GPUs and the astounding frame rates they generate. But we weren't quite prepared for what we saw—and AMD has just lost one of its perennial pluses over Nvidia.

At idle, our test system with the 6990 installed pulled a respectable 148 watts of electricity. This is just slightly higher than the two Nvidia cards (143 and 144 watts), and even lower than the 5970 (154 watts). With the 6990's factory overclocking engaged, we didn't even notice a significant change—149 watts is what our power logger reported.

But at full load, running a version of our 2,560-by-1,600 Metro 2033 benchmark, the base-clocked 6990 used a whopping 413 watts of power—compared to 358 for the reference GTX 580 and 360 for Zotac's version. With the overclocking on, the 6990 leaped up to 446 watts—an average over about three minutes that saw significant time spent upwards of 500 watts. This, more than anything else, chains the 6990 to "fearless enthusiast" territory, a place you shouldn't even consider visiting unless you really know what you're doing and have the hardware to back it up.

In fairness, 2,560-by-1,600 displays aren't that common, even among the hard-core gamer set. Many of them these days have multiple smaller displays instead. But that's just another variation on the same problem, as you have to factor in the juice for the other monitors as well. Any way you look at it, the 6990 is an expensive power proposition—on top of the already dizzying price of entry.

It's also a potentially loud proposition. A lot of power means a lot of heat, and that requires a lot of cooling—and thus a lot of fan noise. Though our Thermaltake case has a lot of fans in it (including one 200mm one in the side panel), we never had any trouble hearing the 6990 during its moments of heaviest processing. For serious users, this isn't that much of a problem—you do get used to it after a while—but we can't claim we didn't notice it.

These are as close as the AMD Radeon HD 6990 comes to flaws, but if you're prepared for them—with a robust bank account, power supply, and strategy for cooling your case and dampening the noise that comes from it—then this card is completely worth it. For everyone else, the more-conservative (and, at right around $500, less-expensive) GTX 580 is a better choice: It's the best single-GPU card out there, will cost less both upfront and over the long haul, and doesn't have quite the noise issues we saw (heard?) with AMD's dual-GPU card. And if Nvidia's own rumored two-GPU product comes to fruition soon, Nvidia's single-GPU performance advantage could catapult that card into the lead. But until then, as the 6990 is capable of playing pretty much every game currently on the market with all the settings cranked to the skies, something the GTX 580 simply can't do as well, we rank AMD's card as a superlative piece of hardware that well-off gamers will rightfully cherish for a long time to come.