Now that both AMD and Nvidia have dual-GPU videocards on the market, quad-GPU CrossFireX and SLI setups are possible—that is, if you have the motherboard, the power supply, the money, and can actually find two dual-GPU cards.
Representing quad SLI, we have two relatively compact Nvidia GeForce GTX 590s. In the quad-CrossFireX corner are two of AMD's hulking, foot-long Radeon HD 6990s. Both pairs cost about the same—an astronomical $1,500, give or take—but which is the better option?
We ran our standard game tests on a Core i7-990X six-core PC with an Intel DX58SO motherboard and a 1,200W Corsair PSU. We used the faster CPU so that massive GPU horsepower would spend less time waiting. The 1,200W PSU is needed to drive these monster cards, which require dual 8-pin PCI Express power connectors.
Our normal gaming runs are at 1920x1200, with 4x AA enabled and all detail levels maxed out. The synthetics are there for comparison, but we play games, not benchmarks. If you just look at the numbers, the quad-GPU cards are screamers. These settings just aren't challenging.
When comparing quad-SLI to quad-CrossFireX, the numbers favor Nvidia, but the frame rates are staggeringly high for both systems. Clearly, Nvidia's done some work with its drivers since the initial release of the GTX 590. Paired GTX 590s won six of nine game tests.
Winner: Quad SLI
Since neither quad-GPU setup had to work hard at 1920x1200 with 4x AA, we had to push them a little harder. After all, if you're spending $1,500 or so for a pair of graphics cards, surely another $1,300 for a 30-inch monitor is within reach.
We ratcheted up the pain, pushing our gaming tests (and Unigine's Heaven benchmark) to 2560x1600 and 8x AA. That's 4 million pixels at 8x AA (with 16x AF). Shaders and detail levels were also maxed out, putting tremendous stress on the overall bandwidth of the system.
At these extreme levels, we still saw stunning frame rates. The competition seemed a little more even, possibly due to AMD's larger frame buffer (2GB per GPU versus 1.5GB per GPU for Nvidia) and the higher clocks. However, AMD seems to have a problem with Dirt 3, so what might have been a tie goes to Nvidia.
Winner: Quad SLI
A good 1,200W PSU is essential for a quad-GPU setup, particularly if you plan on overclocking the CPU and GPUs. That increases the cost of your rig.
On pure power draw, the quad CrossFireX draws a little less power under full load—774W versus 800W for the dual GTX 590s. However, the idle-power draw was substantially lower for paired GTX 590s, which drew just 113W at idle versus 171W for quad CrossFireX. Since systems generally run idle most of the time, that power draw can add up.
What about noise? At full throttle, both of these setups get pretty loud. But the quad CrossFireX cards, with smaller fans that spin up to very high speeds, sound like small jet engines throttling up for takeoff. AMD's HD 6990s are loud even in single-card setups. Paired 6990s are painfully loud.
Winner: Quad SLI
Both quad-GPU systems had trouble running Dirt 3. The Nvidia setup could run the game but not change resolution in-game, while the CrossFireX setup wouldn't run at all. Single- and dual-GPU systems run the game flawlessly.
With the AMD quad setup, you'll need to occasionally download game profiles for CrossFireX. Nvidia builds these into driver updates, but the green machine is now updating drivers on a monthly schedule to match AMD.
Flexibility of installation is a problem, too. The Radeon HD 6990s are a full 12 inches long, while the GTX 590 cards are 3/4 of an inch shorter. That 3/4-inch makes a difference in some cases. So you'll need to pay attention to your internal case dimensions.
In the end, the dual GTX 590 setup is simpler to manage, easier to install, and better mannered.
Winner: Quad SLI
Quad-GPU setups define the extreme in graphics hardware. If you're running games on multiple displays, with stereoscoic 3D turned on, quad GPUs will give you the horsepower to hit smooth frame rates.
If you're running on a single display, though, quad GPUs might be more hassle than they're worth. Toss in the excessive power, the hot air filling your room, and the loud fan noise, and you may want to reconsider—and that's before you see the price tag.
In the end, unless you are running an extreme display configuration, a pair of single-GPU cards will give you as much peformance as you need in cutting-edge games. And you can build a dual-GPU rig today without worrying about product availability.
If you decide that a quad-GPU is right for you, we're pretty bullish on two GTX 590s in quad SLI. It uses a little more power at full load than the AMD alternative, but it's easier to manage and install and seems to have fewer issues with games.
2x Asus GTX 590 (Quad SLI)
2x Radeon HD 6990 (Quad CFX)
||2x Asus GTX 590 (Quad SLI)||2x Radeon HD 6990 (Quad CFX)|
|1920x1200 with 4x AA||2560x1600 with 8x AA|
Unigine Heaven 2.5 (fps)
F1 2010 (fps)
Battleforge DX11 (fps)
Far Cry 2/Long (fps)
Hawx 2 DX11 (fps)
|Just Cause 2 (fps)||63||80||60||
|Dirt 3 (fps)||141||
Best scores are bolded. Our test bed is a 3.47GHz Core i7-990X Extreme Edition in an Intel DX58SO2 motherboard with 12GB of DDR3/1333 and a 1,200W Corsair AX1200 PSU. The OS is 64-bit Windows Ultimate.