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The RV420 Architecture

The RV420 is derived from the R420 making it feature complete with its big brother. For a run down of the R420/X800 architecture, users are encouraged to take a look at our coverage of the X800 launch. The key differences from the previous R300 generation is the support for Shader Model 2b and 3Dc.

In a conversation with ATI back at the X800 launch event, they stated that the R420 architecture was scalable with each rendering quad being independent which gives ATI the ability to turn each off as needed to scale the product. The first example we have seen is the X800 Pro, a 12 pipe part. ATi stated that the R420 architecture was scalable from 4 all the way to 16 pipes. One of the benefits with this approach as opposed to discrete cores for each segment of the market is that defective parts can simply be pushed down the line; an example being one set of the quads has a problem but instead of throwing out the chip, ATI can just turn off that particular quad and turn the chip into a 12 pipe part. This sounded like a fantastic idea except that ATI did not really have all too many failing parts; anecdotal evidence with the success of the VIVO XT800 PRO cards being moddable to full 16 pipe parts is a suggestion that this is probably true.

By foresight or by chance, ATI's RV410 is not simply a slightly broken R420 core. Besides having a different manufacturing process, the R420 is a native PCIe part and only contains 8 pipelines. ATI has a slightly different approach than Nvidia with regards to the PCIe/AGP issue - ATI believes making cores with AGP or PCIe specific cores while Nvidia relies on their HSI chip to convert between the two protocols. Remember that the original X800s were native AGP parts.

One big advantage that the X700 has over the 6600GT is that all the vertex pipelines from the R420 series are kept intact on the X700. The 6600GT saw the number of vertex engines chopped from the 6 of the 6800 series to 3 on the 6600s. ATI's stance is that this will help out mainstream cards as there will be more slower CPUs on mainstream cards.

The Card

The X700 series should all be based on the same board layout. We only have the X700 PRO at the moment but the layout of the XT is not expected to be any different. Size-wise, the X700 is almost exactly the same size as the X600. The heatsink however, is much bigger and is a bit oddly shaped. It comes in a shiny finish that does not quite have a mirrored look. No external power is required on the PCIe version although ATI confirmed that the AGP version will need to be connected to a power dongle. The usual DVI, VGA and TV-Out ports are found on the back of the card.

The X700 is of average size