ATI Radeon R600

R600 Technical Aspects


Techinical Aspects

Now onto the Technical bits that make up the r600. As I said earlier this is going to be a brief run-through and not a University dissertation on r600.

Unified Shader Architecture

The R600's design is similar to the xbox360's GPU as it is based on the Unified Superscalar shader architecture.

The Unified Shader Architecture coupled with Microsofts new DirectX 10 API allows the shaders to be 'unified'.
What this means is that instead of having a fixed number of shaders assigned to certain tasks, (eg x1900: 8 vertex shader processors & 48 pixel shader processors) they can be assigned depending on the job at hand meaning all of the shaders are used.

As a result, the GPU will be fully utilised and therefore performance will be enhanced, gaining up to 25% in performance.


Unified Superscalar Shader Architecture

  • 320 stream processing units
    • Dynamic load balancing and resource allocation for vertex, geometry, and pixel shaders
    • Common instruction set and texture unit access supported for all types of shaders
    • Dedicated branch execution units and texture address processors
  • 128-bit floating point precision for all operations
  • Command processor for reduced CPU overhead
  • Shader instruction and constant caches
  • Up to 80 texture fetches per clock cycle
  • Up to 128 textures per pixel
  • Fully associative multi-level texture cache design
  • DXTC and 3Dc+ texture compression
  • High resolution texture support (up to 8192 x 8192)
  • Fully associative texture Z/stencil cache designs
  • Double-sided hierarchical Z/stencil buffer
  • Early Z test, Re-Z, Z Range optimization, and Fast Z Clear
  • Lossless Z & stencil compression (up to 128:1)
  • Lossless color compression (up to 8:1)
  • 8 render targets (MRTs) with anti-aliasing support
  • Physics processing support

Now I don't need to say that the 2X00 series support DX10 fully with full SM 4.0 support. This is ATI's first card supporting the new Microsoft API and they've followed their Xenos Xbox 360 chip in making r600. In saying that, r600 has taken Xenos that bit futher and gone with a completely unified shader architecture, something nVidia have also done with G80.

The r600 consists of 320 independent stream processing units, made up of 64 superscaler shader processors, each a five-way unit. These all support FP32 bit precision in mathematical operations. Added in are 16 texture units (TMU's) and 16 ROPs (render backends). The 2900 XT has a 512mb ring-bus architecture, taken forward from r580, which can break through 100BG/sec; the same as the G80 can, but at a more interesting price-point.

ATI have also added a "programmable tessellation unit". This is notable as the current DX10 specification do not include this, although Microsoft is said to have plans in including it at a later stage.

Shader Units

ATI have gone a different router to nVidia in as far as their Shader Units are concerned. This isn't in so much as the actual number (though they do differ), more the approach to the way that each stream processor is layed out. r600 uses a 5-way superscaler shader processor, with 5 parts and 5 instructions per clock. These sit in clusters of 16 shaders (80 stream processing units each cluster altogether) and added to them is a branch execution unit. Added is a 64KB memory read/write cache which can be accessed by any shader cluster. This means that in DX10 architecture you can avoid going through the render backend and write straight to memory.

r600 shader

So that's the big difference in architecture of the stream processing units as I see it. ATI have added a lot of additional features, but as this is a brief article, I will leave you to click on the links I have provided below for a more in-depth analysis of the architecture. Now onto what some of this means.
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Most Recent Comments

16-05-2007, 14:03:07

Great work mate. Nice and simple and easy to understand while getting the key points across

Hope everyone enjoys reading it Quote

16-05-2007, 15:00:09

Great article, cant wait for the review.


16-05-2007, 16:09:29

Good work on your first write up matey!

Once again I cannot wait for the view, equk.. are you doing the review too?Quote

16-05-2007, 16:32:16

No I'm doing that Quote

16-05-2007, 16:35:56

Originally Posted by name='Kempez'
No I'm doing that

Suprise suprise.. Kemp always gets his hands on the best stuff!

Good on ya mate!Quote

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