Using multiple graphics cards for more graphics power is not a new concept. In the early days of 3D graphics, 3dfx pioneered multi-graphics card technology. But with the demise of 3dfx, consumer-level multi-graphics card technology was unavailable, even though ATI has been manufacturing multi-card systems for industrial simulators since the Radeon 9700. The consumer has recently been reintroduced to this technology with the release of Nvidia's SLI solution, and more recently, ATI's Crossfire solution. Using multiple graphics cards together provides sufficient graphics performance to support highest visual quality settings and resolutions. However, the choice to purchase a multi-card solution is not a simple one.
First, power and heat have to be considered; multi-card solutions require a great deal of energy, and therefore an expensive high-output power supply unit is a must. In addition, graphics cards produce a lot of heat, and careful attention must be paid to the PC case and cooling equipment to ensure that the system does not overheat.
In addition, remember that SLI/Crossfire requires a motherboard that supports them (usually either one), which can cost a premium compared to single-card/single-slot solutions. Nvidia's SLI will only work on certain nForce4 motherboards, while ATI's Crossfire solution will work on ATI's Crossfire chipsets and even Intel motherboards with a certified multi-card chipset. On the downside, some Crossfire setups require one of the graphics cards to be a special Crossfire edition card. Since the launch of Crossfire, ATI has enabled software Crossfire through the PCI Express bus with some models and is continuing to increase the number of combinations with further driver revisions. The "master" cards for the non-software Crossfire combinations cost a premium over a regular card. Currently, the Radeon X1300, X1600 and X1800 GTO do not require Crossfire edition cards for the dual-graphics Crossfire mode to work.
There are other factors to consider as well. While two graphics cards linked together will offer a performance boost, the result is rarely anywhere near twofold, so from a budgetary standpoint, it is important to keep in mind that paying twice the money will not yield cost effective results. A 120% - 160% performance increase is a more realistic expectation with multi-card solutions - while in some cases performance will not increase at all. For this reason, multi-card solutions usually don't make sense when using cheaper graphics cards, because a more expensive card will almost always outperform a pair of cheaper ones. With this in mind, SLI/Crossfire solutions do not make sense for most consumers. When one is looking to enable more image quality features or to run games at extreme resolutions such as 2560x1600 that is generating over 4 million pixels per frame, solutions like these are the only answer.