ATI's 512-bit Ring Bus and R520 Product Naming

Given the fact that ATI rumors are a dime a dozen these days, when I received the initial ATI market advisory for R520 this week, I somewhat disregarded it -- ATI changes their roadmap plans faster than I change my socks. However, with the copious amounts of incorrect speculation lately, we decided to go ahead and produce another roadmap update. Here is a glimpse of the confirmed cards launching in the upcoming months.

ATI Radeon X1800 (R520)

• Radeon X1800 XT Crossfire Edition

• Radeon X1800 XT

• Radeon X1800 XL

• Radeon X1800 Pro

The 90nm R520 components will come in three flavors as we mentioned earlier, all with the X1800 Radeon moniker. The available marketing information claims that the GPU uses an "ultra-threaded quad-core 3D architecture" and a "512-bit ring bus" memory controller. There's definitely some marketing hyperbole going on there, but let's get into the details.

Those of you who know a little bit about GPU architecture should recognize the "ultra-threaded quad-core" design as a standard GPU. X800XL/XT would also qualify as ultra-threaded and quad-core, as would the 6800GT/Ultra. They have a core split up into groups of "quads" - four pixel pipelines that can be deactivated as a group in case one of them is faulty. Our understanding from the documentation is that there are once again four quads, so expect to see 16 pipes on this card. There are some "confirmations" of 24pp and 32pp, but the roadmaps clearly say four cores/quads (at least to begin with) due to yeild. All signs indicate that a future generation, R580, will use six cores instead.

The 512-bit internal ring bus actually excites us the most; Cell's Elemental Interface Bus (EIB) uses a 16-byte wide quad ring bus, capable of transferring 16-bytes per cycle to the various SPEs. R520's ring bus would actually be four times wider than the bus found on Cell; though this implementation is in R520's memory controller rather than the PPE-to-SPE interface. With all the hype for R520 so far, everyone is banking on the memory controller to put X1800 ahead of G70. However, there is once again some hype occurring. The memory subsystem is still connected by a more typical 256-bit memory bus, and the 512-bit ring bus is something else. We'll have to wait for actual cards and benchmarks before we can really discover how the card performs.

Other interesting technologies on R520 include Shader Model 3.0 (and thus HDR), Adaptive anti-aliasing, and up to 512MB of GDDR3 memory. Our sources indicate that only the Crossfire versions of X1800 will support 512MB initially, but this may change further downstream. Radeon X1800, X1600 will also feature ATI's Avivo^TM technology, which we currently cannot discuss further. There was also indiciation in the roadmap that this generation of ATI cards will fully support Windows Vista, with beta drivers already available.

Radeon X1600 (RV530)

• Radeon X1600 XT Crossfire Edition
• Radeon X1600 XT
• Radeon X1600 Pro

X1600 is very similar to X1800 with respect to features, although there will be different clocks and pipelines. The roadmap lists a 256-bit internal ring bus, whereas the X1800 models will have a 512-bit bus instead. The external memory bus will be half as wide as well: 128-bits vs. 256-bits. Obviously, with fewer quads the need for a wider bus is diminished, and the X1600 only has three quads (12 pipes). To our knowledge, everything from RV530 and lower is virtually identical to the roadmap we published a few weeks ago, with a few of the launch dates pushed back.

Radeon X1300 (RV515)

• Radeon X1300 Pro

• Radeon X1300

• Radeon X1300 HyperMemory

Our original roadmap from just a few weeks ago claimed an "LE" version of RV515, but it appears this has been replaced with just an RV515 "vanilla" offering instead. Since then, we have also gotten wind of a HyperMemory card. If priced right, a high performance HyperMemory card from ATI could really give NVIDIA a run for their money on the low end; NVIDIA's GeForce 6500 is the upcoming TurboCache replacement. The roadmaps also indicated Crossfire on X1300, but so far there are no Master Cards slated for RV515.

Several of ATI's AIB partners told us that there will be no Radeon X800GTO2 recently. There might be an exclusive deal lined up for a specific AIB, but all signs seem to indicate that X800GTO and X800GT are the short term products that are supposed to replace X800XL, and that inventory of the 90nm components should be widely available before the EOL of X800GTO.