Just two short weeks ago Nvidia launched their new GeForce 6800 Ultra graphics card along with their NV4x architecture. Today ATi introduces their X800 family of graphics cards based on the R420 architecture. Expectations for both new architectures were high and Nvidia’s GeForce 6800 Ultra certainly did deliver, offering twice the performance of the then fastest shipping graphics accelerator, ATi’s Radeon 9800 XT. Obviously ATi is hell bent on getting the title back from Nvidia and to, once again, proclaim itself the king of 3D graphics. In the next few pages we’ll explore what ATi’s latest has to offer and whether that’s enough to dethrone the GeForce 6800 Ultra.



Fig 1. The two contenders to the 3D graphics throne, GeForce 6800 Ultra and Radeon X800 XT.
But before we get into that let’s discuss briefly what the R420 architecture brings to the table. In essence the R420 architecture is a further development of the R360 architecture which debuted with the Radeon 9600 XT and 9800 XT graphics cards. This doesn’t mean ATi simply increased the clockspeeds of the R360 architecture and applied some minor enhancements here and there, like they did when moving from the R300 to the R360 architecture. The R420 architecture, although based on the R360, is using parts of that architecture but has been reworked to offer over twice the performance of that architecture.

The design goals for the R420 architecture as set forth by ATi were to increase the performance and up the efficiency. This meant that ATi hasn’t opted for including new features such as shader model 3.0 support for 32-bit rendering throughout the pipeline, as found on Nvidia’s NV4x architecture. They did however all that was needed to wring every last bit of performance from the features they did include. For example the R420 architecture uses quad 64-bit memory controllers and a 16-stage pixel pipeline which can be scaled from 4 to 16 stages in steps of 4. This means that ATi can manufacture a whole range of different graphics accelerators based on a single architecture. ATi also included a new texture compression technique, 3Dc, which is hardware accelerated to further up the performance.