ATI launches R420

ATI today began shipping its next-generation graphics chip, the R420, as the Radeon X800 Pro, with a faster version, the equally anticipated Radeon X800 XT Platinum Edition, to ship later this month.

As expected, the R420 supports up to 16 pixel pipelines arranged in four banks of four. The X800 XT will provide the full array, but the X800 Pro will have only 12 pipelines enabled. Both have six vertex pipelines yielding up to 12 vertex shader ops per clock.

The chips are identical - ATI simply sifts through fresh R420s those with less than 16 operational pipelines are offered under the Pro brand, in much the same way CPU vendors separate dies out according to the fastest clock speed they will support.

ATI architecture specialist Raja Kuduri told The Register that each unused bank for four pipelines is physically fused after sorting - so don't expect to be able to get an X800 Pro to run like an XT, he warned.

Speaking of clock frequencies, the X800 Pro is clocked at 475MHz, with memory running to 900MHz. The X800 XT core runs at 520MHz and is connected to 1.12GHz memory - higher than their rivals, the GeForce 6800 and 6800 Ultra, respectively. Both ATI chips connect to memory across a 256-bit bus comprising four 64-bit channels and support GDDR 3 SDRAM. Both will ship with 256MB of RAM on ATI's retail boards, which will retail for $399 and $499, respectively. The R420 supports AGP 8x.

Both chips contain 160 million transistors - rather less than Nvidia's 220 million-transistor GeForce 6800 - and are fabbed at 130nm using low-k dielectric materials.

Boards based on the R420 will happily sit within the space of a single AGP slot, ATI said, and require only a 250W power supply. According to ATI, running 3DMark01 continuously results produces an average continuous power draw on the X800 Pro of 58W and 76W on the X800 XT. Run the same test with 3DMark03 and the average continuous power draw on the X800 Pro and X800 XT drops to 49W and 65W, respectively.

ATI claims a 100-200 per cent performance increase over its previous generation of GPU, the Radeon 9800XT, and gains of up to 60 per cent over a "competitor's next-gen GPU" - presumably, but not confirmed as the NV40. However, we look forward to the results of independent tests.

The R420 contains next-generation SmartShader, HyperZ and SmoothVision engines, all now carrying the 'HD' suffix. SmartShader HD - the pixel processing engine - contains 32 temporary registers, up from 12 in the previous generation, and now supports shader code of up to 1536 instructions in length, up from 160.

The engine's texture unit adds ATI's 3Dc 'normal map' compression technology - a crucial addition that ATI hopes will compensate for SmartShader HD's lack of support for DirectX 9.0's Pixel Shader 3.0.

HyperZ HD supports hierarchical z buffering at up to 1920 x 1080 and can handle up to 32 z-buffer/stencil ops per clock.

SmoothVision HD adds a new anti-aliasing mode: temporal anti-aliasing. It uses frame-by-frame pixel persistence - the pixels stay the same over two frames - to yield and effective doubling of the anti-aliasing level. So, 2x yields 4x when temporal anti-aliasing is enabled. Because of the dependence on persistence, temporal will only work at frame rates of over 30fps and when VSYNC is enabled, ATI said.

The X800 Pro begins shipping to ATI customers today. Boards based on the part are expected in 10-14 days, the company said. The X800 XT is due to ship to board makers on 21 May. ®

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