AMD is trying something new with its Radeon HD 6900 series of graphics cards. Instead of its usual tactic of addressing the higher end of the market with a graphics card containing two of the GPUs powering the Radeon HD 6870 (a chip code-named Barts), it is using a single, larger, more-powerful new GPU. Code-named Cayman, this new GPU doesn't merely take the architecture of the Radeon HD 6800 series and scale it up; rather, it makes significant architectural changes. AMD has redesigned the shader units for improved efficiency, greatly enhanced geometry performance, and employed a whole new power-management system.
The results are mixed. The Radeon HD 6900 series cards are certainly fast, though the 6970 doesn't always fare better than the Nvidia GeForce GTX 570 against which it is priced to compete. Anyone hoping that AMD would reclaim the absolute speed crown from Nvidia will be disappointed. Both the Radeon HD 6970 and the Radeon HD 6950 are quite long, too, and won't fit in smaller PCs (as is often the case with high-end enthusiast cards). Nevertheless, they offer good power efficiency for their class, as well as lots of other interesting features.
At almost 400 square millimeters, the GPU powering AMD's new graphics cards is the largest the company has produced in a long time, but it's still about 26 percent smaller than the GPU in Nvidia's latest cards. It features a lot of texturing power and high clock speeds, but fewer render back-ends than Nvidia's cards have. Note that the Radeon HD 6950 and 6970 feature 2GB of RAM, a step up from the 1GB we usually see on AMD cards; the extra RAM will help in intensive games running at high resolution.
Note, too, the discrepancy between the numbers of shader units for the AMD and Nvidia cards in the chart above; that discrepancy exists because the numbers are not directly comparable. Due to the different way the Nvidia and AMD chips are designed, a single shader unit from Nvidia is capable of doing more work than one in AMD's chip. An Nvidia shader unit is also larger, and therefore not as many of them are present in the GPU.
Next: A new architecture from AMD