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Plummeting prices and advances in motherboard technologies are making dual-card graphics a must-have for serious gamers.
Two competing technologies, ATI Technologies' CrossFire platform and Nvidia's Scalable Link Interface, or SLI, let a pair of graphics cards work side by side to essentially double a PC's graphics-processing firepower.
Such systems could cost $1,200 or more when they first became available from ATI and Nvidia last year. But now gamers who make a relatively modest investment can easily tap the improved resolution and faster frame rates that dual-card systems offer.
They'll get more-realistic renderings of complex graphics, ranging from smoke to human facial features, in games such as Doom 3, FarCry and The Elder Scrolls IV: Oblivion, which rely heavily on graphics processing for their visual magic.
Running two cards "doubles everything," said David Kirk, Nvidia's chief scientist, in an e-mail about the company's SLI dual-graphics-card platform. "This increases the amount of geometry, textures and other data that can be transferred to the graphics cards per frame."
That means fire will look more like real flames and less like an animated cardboard cutout in a Scooby Doo cartoon. Higher frame rates let gamers splatter monsters faster and allows them to set their games to the maximum resolution with less risk of system instability.
Using two graphics cards can also improve a gaming rig's anti-aliasing capabilities, making the outer lines of images less jagged. When entering a room in Doom 3, for example, the edges of a door will look smoother.
"The great thing about graphics processors is their instant scaling, which is a very parallel operation," said Raja Koduri, an ATI hardware engineering team leader. "Even with two low-end cards, which offer 50 gigaflops (per second computing speed), you get 100 gigaflops when you put two graphics cards together."
The availability of PCI Express motherboards, which offer an extra card slot and allow data to be transferred between two graphics cards at a fast data rate, triggered this year's wide-scale rollout of dual-card graphics.
By using the fast data-flow capabilities that PCI Express motherboards offer, two graphics cards can rapidly exchange data, effectively sharing graphics-processing computational tasks. CrossFire and SLI cards split image-rendering tasks so each card processes part of an image's data. Though similar, the two technologies handle things differently. And because performance depends on the application involved, there is no clear choice about which technology works better overall.
According to Jon Peddie of Jon Peddie Research, almost all add-in motherboards sold today offer PCI Express, except for very low-end systems. "(Dual-card capabilities) are part of every graphics processor chip made (these days)," Peddie said.
The concept of dual-card graphics is nothing new, but previous iterations simply failed to make the mainstream. A company called 3DFX, which Nvidia eventually bought, introduced dual-card graphics several years ago, but the technology suffered technical hurdles and never took off with motherboard makers. Nvidia introduced its first SLI card almost two years ago, but it was not until last year that ATI and Nvidia dual-card graphics became nearly ubiquitous, mostly tied to motherboard availability.
Even with today's systems, there are caveats. Don't expect dual graphics cards to offer much improvement in older titles such as Quake 3, Unreal Tournament or Half-Life 2, or in other games that rely more on CPU computation and less on graphics processing. The frame rates might even decrease when playing some older games using SLI or CrossFire dual-graphics cards compared to using a single card, especially if the monitor resolution is set to a low value.
Despite those shortcomings, component makers are betting on increased demand for multiple-graphics-cards systems. High-end motherboards with four or more graphics-card slots will see wide-scale deployment next year, ATI's Raja said. Indeed, Nvidia already sells quad-SLI-enabled graphics cards, but adoption remains limited to the ultra-high-end gamer set due to high cost, availability of motherboards and driver issues.
