Good Things in Small Packages

As indicated earlier, the ATI Mobility Radeon 9800 is based on the R420 core, which powers ATI's latest X800 line of GPUs. In the past, naming may have been a bit of a stretch in terms of comparing mobile graphics solutions with their desktop counterparts, but this time around, the MR9800 bests the desktop 9800 cards in feature set (and doesn't fall that incredibly far behind in performance as we'll soon see).

The MR9800 actually supports all the features of the Radeon X800, as it is simply a cut down version of the chip with some enhanced power management features. The real difference between current X800 GPUs on the market and MR9800 is in pixel/vertex pipelines featured. The new mobile chip has 8 pixel pipes and 4 vertex pipes. This also makes the MR9800 look more like a desktop 9800 in fillrate and processing power per clock cycle (though the R420 core will be more efficient). ATI also points to their new chip as the first mobile part to support 256MB of memory using a 256bit wide memory interface. This feature is also a result of the larger power budget available to ATI when targeting the DTR space.

To get a good idea of what's under the hood of MR9800 (and just how alike the desktop X800 really is), here's a block diagram of the chip from ATI's presentation on the part:



Even though ATI had a larger power budget to work with than usual, they couldn't ignore the fact that people will want to be able to use the battery in their system at some point, and thermal and power management both still play a large role in the DTR space. In order to satisfy these needs, ATI's mobile team worked alongside their desktop team to bring power and thermal management features to MR9800 through the R420 design cycle. This allows the R420 to fully support ATI's Powerplay technology right out of the fab. This is why we're seeing the release of a mobile R420 part so soon after the desktop release.

Powerplay is made up of a couple different features. To highlight, we'll touch on a few here. With Power-on-demand, ATI can dynamically adjust clock speeds and voltages based on the usage of the GPU at any given time. This will help to extend battery life when not pushing the graphics subsystem, as will user controlled GPU power management settings. Another important power/thermal management feature of Powerplay is Clock Gating. This amounts to the ability of the GPU to turn off parts of itself when not in use. The granularity of this capability is illustrated in the following slide from ATI's presentation:



We know that in the past, in order to play video, ATI couldn't completely turn off the 3D pipeline, but we are not sure if they have altered this limitation in the MR9800. We'll look into the matter in the future, but this question should answer itself (in video playback tests) when we start seeing reviews of notebooks featuring this GPU.

That does it for the technical details; it's time for some numbers.

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  • TrogdorJW - Thursday, August 19, 2004 - link

    What are teh actual specifications of the MR9800 as configured in the Dell XPS laptop? I assume it had 256 MB of RAM with a 256-bit bus, but what was the clockspeed of the RAM and the GPU core? I'm betting lower clocked RAM is a major reason that the MR9800 sometimes falters in performance. Reply

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