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  ATIís Radeon X1000 series, what to expect? 
  Sep 30, 2005, 07:30am EDT 
By: Sander Sassen

Next week weíll see the introduction of ATIís R520 architecture in the form of a whole new top-to-bottom generation of graphics cards which will be dubbed the X1000 series. The X1000 series starts off with the top-of-the-line Radeon X1800 XT and has the low-end X1300 closing the ranks. ATI has put all their engineering effort towards a new graphics accelerator architecture based on the 90-nm process. Key features include SM3.0 support, a 512-bit ring bus memory controller and support for their recently introduced Avivo platform. In these next few paragraphs weíll be giving you an exclusive first look at what ATI will be introducing next week.

R520 architecture

The focus of ATIís new R520 architecture has really been on efficiency, making sure that all clock-cycles are put to good use and creating minimal overhead. Unlike previous rumors indicating the architecture had up to 32-pipelines, the actual number is 16-pipelines or pixel-shader processors, with 8-vertex shader processors. Obviously the pixel-shader processors have been upgraded to provide full support for SM 3.0. But thereís more; ATI added dynamic flow control to streamline processing and multi-threading support, the new architecture now allows for 512 pixel-shader threads to be outstanding. The vertex-shader processors have also been updated; theyíre now able to process two shader instructions per clock and handle up to 10-billion instructions per second.

The large number of outstanding pixel-shader threads, 512, is actually one of the strengths of the architecture as threads are spread out across the pixel-shader processors and are executed in parallel. A total of 16 pixel-shader processors are available on the X1800, organized in groups of four, hence thereís four shader cores, dubbed the quad-pixel shader cores. The pixels are handled in small 4x4 pixel groups, so the X1800 handles just 16-pixels per thread which makes the thread size small and efficient. Each of the pixel-shader processors can process per thread six different shader instructions on four pixels per clock-cycle. Obviously branch prediction is used to minimize overhead and this is not handled by the ALUs, but by dedicated logic included with ever pixel-shader, further improving efficiency.

A closer look at the R520 architecture, click here for a larger version.

The pixel-shader engine itself is comprised of four quad-pixel shader cores, a number of general purpose register arrays, sixteen texture address units and the ultra-threading dispatch processor. Data gets sent from the setup engine down to the ultra-threading dispatch engine that distributes the load across the four quad-pixel shader cores. The shader instructions are processed with 128-bit floating point precision and make use of the general storage register arrays that serve to increase bandwidth and provide local storage for instructions but also allow for fast thread switching. Due to the dedicated branch execution units per pixel-shader overhead is minimalized. Combined with the dynamic flow control implemented in the ultra-threading dispatch processor all the shader processors are constantly fed with data and can execute in fewer clock-cycles. All in all this looks like an efficient new architecture that can be manufactured cheaply on the 90nm process, in combination with the fewer number of pipelines the die will also be smaller than competing products from NVIDIA.

Shipping products

ATI will launch with immediate availability a number of graphics cards based on their new architecture. The top-of-the-line Radeon X1800XT will be available as of the 5th of November shipping at a 625MHz core and 1500MHz memory frequency. Offered with 256MB and 512MB of GDDR3 memory it will be priced at $499 and $549 respectively. The Radeon X1800XL will be available on October 5th and offers a 500MHz core and 1GHz memory frequency and comes with 256MB of GDDR3 memory with a price tag of $449. All of the Radeon X1800 graphics cards utilize the full 16-pipelines, theyíre just different in terms of memory size and clock speed or both in the case of the Radeon X1800 XL.

The top-of-the-line Radeon X1800 series will ship with a dual-slot heatsink.

The mid-range Radeon X1600XT ships with either 128MB or 256MB of memory, clocks in at a 590MHz core and 1.38GHz memory frequency and can be bought starting November 30th for respectively $199 and $249. All of the Radeon X1600 graphics cards will have to make do with just 12-pipelines. The low-end Radeon X1300 will be offered in three different versions, the $149 Radeon X1300 Pro with 256MB of memory and 600MHz core and 800MHz memory clocks. The $99 and $129 Radeon X1300 with 450MHz core and 500MHz memory clocks and 128MB or 256MB of memory respectively. And closing the ranks is the Radeon X1300 HyperMemory at $79 with 32MB HyperMemory and 450MHz core and 1GHz memory clocks.

The mid-range X1600 and low-end X1300 series will ship with a single-slot heatsink.

The Radeon X1300 Pro and X1300 will be available on October 5th and sadly they will feature only 4 pipelines. Unfortunately no dates have been given for the Radeon X1800 CrossFire Edition or the Radeon X1600 CrossFire Edition. What is clear, though, is that the Radeon 1300 will not feature a CrossFire Edition card, itíll utilize the PCIe bus for communication. Both the Radeon X1800 and X1600 CrossFire Edition will support resolutions up to 2046x1536 pixels with a 70Hz refresh, negating some of the limitations of CrossFire on the Xx00 platform.

That concludes our first look at the R520 architecture and the X1000 series cards that will be available at launch. As for performance weíll have to wait for the actual launch. If ATI is to be believed the Radeon X1800XT consistently outperforms the GeForce 7800GTX in all games, sometimes by as much as 80%. Iím afraid that is pure marketing speak however, as theyíve made bold claims such as these before. I vividly remember when the Radeon X800XT PE was introduced they circulated similar benchmark results showing it besting the GeForce 6800 Ultra by as much as 40%, which of course proved to be just wishful thinking. The preliminary benchmarks weíve provided earlier, run on a pre-production card, will prove to be on the low side however. ATI has already raised the clock speeds and has done some extensive work on their drivers since then, effectively rendering them outdated. However we donít doubt that the Radeon X1800XT will have better performance than the GeForce 7800GTX, even if just by a small margin.

Sander Sassen.

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