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The Radeon R420 core from ATI Technologies was their 3rd-generation DirectX 9.0c-capable Graphics Chip . Used first on the Radeon X800, R420 was produced on a 0.13 Micrometer (130 Nm ) Low-''K'' process and used GDDR-3 memory. The chip was designed for AGP . DEVELOPMENT In terms of supported DirectX features, R420 was very similar to the R(V)3x0 cores. R420 came equipped with over double the pixel and vertex pushing resources as Radeon 9800 XT , with 16 highly-clocked DirectX 9.0c pixel pipelines supporting features for Shader Model 2.0B. This was referred to as a 4 "quad" arrangement. This organization internally allowed ATI to disable defective "quads" and sell chips with 12, 8 or even 4 pixel pipelines, a step forward in the philosophy followed with Radeon 9500/9700 and 9800SE/9800. This separation into "quads" also allowed ATI to design a system to optimize the efficiency of the overall chip. Coined the "quad dispatch system", the screen is tiled and work is spread out evenly among the separate "quads" to optimize their throughput. This is how the "R(V)3x0" chips performed their tasks as well, and R420 refined this a bit by allowing programmable tile sizes to control work flow on a finer level of granularity. Apparently by reducing tile sizes, ATI was able to optimize for different triangle sizes. Around the time of the release of R420, ATI revealed a new Anti-aliasing technology their chips were capable of called Temporal Antialiasing . This new feature took advantage of a Framerate higher than 60 Fps to blur the aliased edges together. By rotating the anti-aliasing sampling pattern and taking into account the minimum of 60 fps refresh of the scene, anti-aliasing effectiveness could be boosted a step. A 2X software setting became effectively 4X, for example. Unfortunately it required the system to be able to maintain at least 60 fps or temporal anti-aliasing would cause a noticeable flickering, where 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. Another notable addition to the core was ATI's then-new Normal Map compression, dubbed "3Dc". Similar to how Texture Compression had been part of the Direct3D specification for years and was used for compressing regular textures, normal map compression compacted this new type of surface detail layer. Because DirectX Texture Compression ( DXTC ) was block based and not designed for a normal map's different data properties, a new compression method was needed to prevent loss of detail and other artifacting. 3Dc was based on a modified DXT5 mode, which in fact was a fallback option for hardware not supporting 3Dc. It was mathematically optimized in various ways for normal maps. Software making heavy use of normal mapping could gain a significant speed boost from the savings in fillrate and bandwidth by using 3Dc. When ATI doubled the number of pixel pipelines, they also upped the number of chip. Interestingly, RV410 significantly outgunned nVidia's GeForce 6600GT (3 vertex shaders) on geometry throughput. On the entire vertex shader angle, with R420's and RV410's 6 vertex shaders combined with vastly higher clock speeds compared to the previous generation, ATI was able to more than double the geometry processing capability that 9800XT had had. Most of the rest of the GPU was extremely similar to R300. The memory controller and memory bandwidth optimization techniques ( HyperZ ) were identical. MODELS Notable Boards The AGP Radeon X800 series was based on the R420 core. The X300 and ''' X600 ''' series, which were little more than PCI Express versions of the Radeon 9600 series, and were intended to be the new mainstream products. X300 was based on RV370, a 110nm chip, while X600 was based on RV380 which used 130nm low-k. Both had identical capabilities, however. Later the Radeon X550 came, a quietly launched addition to the Radeon-X series set to replace the X300 series, using the same chip as X300 (RV370). The X700 (RV410) series replaced the X600 in September 2004. The X700 series has a similar core to the Radeon 9800 Pro but having only a 128-bit Memory interface, clocked much higher and produced on a 0.11 micrometre process. RV410 used an interesting layout, consisting of 8 pixel pipelines connected to 4 ROP s (similar to GeForce 6600 ) while maintaining the 6 vertex shaders of X800. The 110 nm process was a cost-cutting process, designed not for high clock speeds but for reducing die size while maintaining high yields. A '''X700XT''' was planned for production, and reviewed by many sites, but was never released. It was believed that X700 XT set too high of a clock ceiling for ATI to profitably produce. This was primarily a result of the 110nm process not being capable of high clock speeds. X700 XT was also not adequately competitive with nVidia's impressive GeForce 6600GT . The Radeon X800 "R430"-based 110 nanometer series was introduced at the end of 2004 along with ATI's new '''X850''' cards. While the X800 is a great alternative to the failed X700 XT, the new '''X800 XL''' had higher memory speeds and 16 pipelines to boost performance. The X850 series had slightly higher performance than the X800 series due to some minor optimization of the core, and was available in 3 forms: the '''X850 Pro''', the '''X850 XT''', and the '''X850 XT Platinum Edition''', and was still built on the high-performance 130 nm process with Low-K black diamond technology. The X800 XL was equipped with 4 quads (16 pipelines), making it equally endowed with X850 XT. X800 XL was not able to attain nearly as high clock speeds on the cost-optimized 110 nm process. In 2005, ATI had a large number of dies that "worked" but not well enough to be used on the X800 or X850 series cards. So a new SKU was made, the X800GT. It used any "R480" X850 die or "R430" X800XL die that had 8 functional pipes (2 quads) and could run at 475 MHz. They were meant to compete with the 6600GT, Nvidia's performance-mainstream card, a card that the X700 series was soundly outclassed by. ATI also then released the '''X800GTO''', which was a 12 pipe card (3 quads) using either "R480" or "R430" dies again, clocked at 400 MHz. The card performed between the X800GT and the X800XL. It was faster than the plain GeForce 6800 , but considerably slower than GeForce 6800GT. High sales for this card were due to its relatively high performance coupled with a cost only slightly higher than the X800GT and the fact that it had high chances of unclocking the remaining quad. Finally, another SKU was the again-"R480"-based '''X800GTO&2''', which was manufactured by Sapphire. This card usually came with a 12 pipe configuration like X800GTO, but sometimes with all 4 quads enabled. This board was unique in the GTx series in that sometimes the 3 quad boards could be turned into 4 quad boards with a BIOS modification. The last variation of the GTO series was that all 4 quads were enabled on the GTO and were passed off as Special GTO boards such as Powercolor's GTO-16. The GTO and GTO&2 boards were usually overclockable to over 540MHz core, nearly X850 XT PE levels if they were equipped with the "R480" core. Table of Models ''(Sorted by model)'' ''Note: X300 and X600 are based on " R300 " and are not listed here.''
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