R420 basically takes a "wider is better" approach to the previous architecture, with some small tweaks thrown in to enhance it in various ways.

This organization internally allowed ATI to disable defective "quads" and sell chips with 12, 8 or even 4 pixel pipelines, an evolution of the technique used with Radeon 9500/9700 and 9800SE/9800.

This is how the R300-series chips performed their tasks as well, but R420 refined this by allowing programmable tile sizes in order to control work flow on a finer level of granularity.

Normal and parallax mapping were replacing sheer geometric complexity for model detail, so undoubtedly that was part of the reasoning.

With R420's and RV410's 6 vertex shaders combined with higher clock speeds than the previous generation, ATI was able to more than double the geometry processing capability of 9800XT.

Although the R420-based chips are fundamentally similar to R300-based cores, ATI did tweak and enhance the pixel shader units for more flexibility.

By taking advantage of the frame-to-eye effects of a framerate higher than 60 frame/s, the GPU is able to better smooth aliased edges by rotating the anti-aliasing sampling pattern between frames.

Unfortunately, it required the system to be able to maintain at least 60 frame/s or temporal anti-aliasing would cause a noticeable flickering, because the user would be able to see the alternating AA patterns.

However, in games which this performance level could be maintained, Temporal AA was a nice addition to ATI's excellent anti-aliasing options.

Software making heavy use of normal mapping could gain a significant speed boost from the savings in fillrate and bandwidth by using 3Dc.

R420 was actually a secondary 4th generation project for ATI, with the original R400 plan, internally codenamed "Crayola", being scrapped.

[4] The R400 architecture was thus implemented only in the Xenos chip used in the Xbox 360 video game console,[5] and became the base for the Qualcomm Adreno 200 mobile GPU, initially called the AMD Z430.

An X800 Pro VIVO (Video-in-Video-out) was also released and was popular with overclockers because the disabled quad could usually be enabled, resulting in a fully functional X800 XT PE at a lower cost.

RV410 used a layout consisting of 8 pixel pipelines connected to 4 ROPs (similar to GeForce 6600) while maintaining the 6 vertex shaders of X800.

A close relative, the new X800 XL, was positioned to dethrone NVIDIA's GeForce 6800 GT with higher memory speeds and a full 16 pipelines to boost performance.

R430 was unable to reach high clock speeds, being mainly designed to reduce the cost per GPU, and so a new top-of-the-line core was still needed.