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The R520 was the codename for ATI's X1800 card. It's based upon a 90 nanometer low-k dieletic process, the first video card in the industry to make the transition to the new process. Every transition to a new process has some teething problems and ATI's is no exception. The R520 has 322 million transistors, the most of any video chip to date. One clear difference between the X1800XT and the X1900 series is the number of Pixel Shader processors. The X1900XT has 48 Pixel Shader processors, while the ASUS EAX X1800XT has 16 Pixel Shaders. As games get more complicated, the X1900 series will show higher performance than the X1800XT. X1800XT is Pixel and Vertex Shader 3.0 compliant. ATI decided to wait until 2005 to bring SM3.0 into their lineup. Some people may call the decision iffy in light of the fact that NVIDIA cards had SM 3.0 from 2004, a full year before ATI did. In retrospect, the decision may or may not have backfired on ATI as NVIDIA is able to release products quickly based upon the old cores for lower prices (i.e. 6800GS). Key features of Pixel Shader 3.0 include: nearly unlimited shader program lengths (65,536 instructions per pass limited by the API), Dynamic Branching in the pixel shader, and more. To improve flow control, ATI breaks down the pixel processing workload into a large number of small threads. ATI refers to this as ultra-threading. These threads consist of small 4x4 blocks of pixels (16) on which the same shader code is executed. The UTDP can work on 512 threads simultaneously. Vertex Shader 3.0 is an improvement over 2.0 as well. Vertex Shader 2.0 minimum requirements were 256 shader instruction programs in a pass. 3.0 brought that number higher to 512 or more. Dynamic Branching and Looping is also a key part of VS 3.0. The X1800XT has 8 Vertex Shader processors, with an output of 2 vertices a second. This gives the ASUS X1800XT a throughput of 1.4 billion vertices a second. High Dynamic Range is made possible by the floating point processing available on video cards like the ASUS EAX X1800XT. The human eye can distinguish between thousands of possible contrasts. Older cards like a GeForce 2 GTS used integer processing and were limited to a range of 255:1. With floating point calculations, the X1900 can do a contrast ratio 65,535:1. Adaptive Anti-Aliasing is ATI's version of Transparency Anti-Aliasing. Transparent textures like the insides of a chain-link fence, dense vegetation are not Anti-Aliased using normal Multi-Sample Anti-Aliasing. AAA applies Supersample Anti-Aliasing to those textures and Multi-Sample Anti-Aliasing to everything else. ATI's AAA does a good job with chain-link fences. Contents: 
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