Why NVIDIA launched the GeForce GTX Titan when it already has the GeForce GTX 690 dual-GPU card covering the same exact $999 price-point is a question best answered in the realm of multi-GPU. If you haven't read our GTX Titan review covering the product from a single-card perspective already, please do so to get a hold of detailed specifications, features, and performance numbers in comparison to a wider selection of graphics cards.
Current GPU technology only allows you to combine up to four GPUs, which is why you can only pair up two dual-GPU graphics cards: each physical card comes with two GPUs onboard, and you're effectively making four GPUs work in tandem. NVIDIA's $999 GeForce GTX 690 may be a wonderful graphics card that scales near-perfectly in terms of performance, but in the end, you can only pair two of them up. AMD allowed its AIB partners to develop dual-GPU cards on their own by using pairs of HD 7970 GHz Edition chips and some of them have managed to dethrone the GTX 690.
This is perhaps where the GTX Titan steps in. Priced at the same $999, it is a single-GPU graphics card based on NVIDIA's GK110 silicon, and you can combine up to four of them, which absolves the GTX Titan of the need to match up to the GTX 690 in terms of single-card performance.
In today's GeForce GTX Titan review, we are testing how well GeForce GTX Titan 2-way (2 cards) and 3-way (3 cards) SLI configurations fare against GTX 690 Quad SLI (2 cards, 4 GPUs), GTX 680 2-way and 3-way SLI, and AMD Radeon HD 7970 GHz Edition 2-way and 3-way CrossFireX configurations. Performance numbers of each of the contenders' single-card configurations are also tossed in.
The Intel Core i7 "Ivy Bridge" test-bed we normally use for our graphics card reviews won't do justice to 3-way configurations, so we set up a new Intel Core i7 "Sandy Bridge-E" test-bed running an Intel X79 chipset motherboard, which gives each of the three cards a PCI-Express x16 connection of its own. All other data-points in this review were measured on the same test bed.