ATI Mobility Radeon 9000: Raising the bar againby Matthew Witheiler on August 29, 2002 5:00 AM EST
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Radeon 9000, Take Two
Many of the high performance mobile video parts in the market today are based off of technology initially implemented on the desktop side. Both ATI and NVIDIA have historically taken mid-end desktop graphics chips, thrown in some power saving circuitry, and produced a high-end mobile part. For example, NVIDIA's latest generation mobile chips, the GeForce4 Go series chips, are essentially GeForce4 MX chips. And ATI's Mobility Radeon 7500 chips; they are basically the same as the desktop Radeon 7500. This makes the most sense for the graphics companies, as they are able to use almost the same chip in two different markets: the mainstream desktop market and the high-end mobile market.
We can think of the Mobility Radeon 9000 as the mobile equivalent of the Radeon 9700 in terms of product hierarchy. Both chips are targeted at the high-end range of their applications, both chips bring new and important features to their platforms, and both chips are extremely impressive. On the other hand, in terms of chip design, we can think of the Mobility Radeon 9000 as a Radeon 9000 (RV250) because that is essentially what it is.
The Mobility Radeon 9000 is an RV250 core with power saving circuitry enabled. This gives the mobile chip the same feature set as the Radeon 9000. Let's go over those features again briefly, but please do look at our Radeon 9000 review for even more details on the RV250 GPU.
The RV250 core is actually a new chip design from ATI and is based on a scaled down version of the R200 core that powered the Radeon 8500. In order to decrease manufacturing costs ATI removed one texture unit from each of the R200's pipeline to make the RV250 core. This leaves the RV250 with four pixel pipelines and one texture unit per pipeline, resulting in a much smaller die size. Although important on the desktop market to keep cost down, the small die size of the RV250 has even more advantages in the mobile arena where the small die means a smaller chip package and a less power hungry chip.
The RV250 core powering the Mobility Radeon 9000 actually improved upon the Radeon 8500's R200 core in a number of ways. One of the more tangible improvements that the RV250 holds over the R200 is an upgraded triangle setup engine. This should improve the performance of the chip in situations that are not texel fetch bound. Also added in the RV250 core is support for ATI's FULLSTREAM technology, giving the R200 the ability to run pixel shader programs on video streams. Using FULLSTREAM and supported video playback software (only RealPlayer at time of publication), ATI can smooth out the blocky compression artifacts that are normally seen in low bandwidth video. This is done by running an AA (anti-alising) type program on the incoming stream of a video.
Video before FULLSTREAM has been applied.
Video after FULLSTREAM has been applied.
ATI also told us that they reworked the internal caches of the chip to make it more efficient but, due to a lack of public documents on the subject, we are unable to figure out exactly what went on.
Since the only thing removed from the R200 core to make the RV250 was a single texture unit from each pixel pipeline, what wasn't added to the RV250 GPU was borrowed from the R200 chip. These borrowed items include the R200's HyperZ II technology, Hydravision support, anisotropic filter, supersampling AA engine, and, most importantly, full DirectX 8.1 support.
The DirectX 8 programmable pixel and vertex shader support is probably the largest advantage that the Mobility Radeon 9000 has over the competition. You may recall that the NVIDIA GeForce4 Go series chips, based off of the GeForce4 MX desktop core, cut costs by taking out all DirectX 8 programmability. This left both the desktop and mobile versions of the NV17 core without the DirectX 8 support that many new games are starting to require. The Mobility Radeon 9000 uses the R200's Charisma Engine II to bring to bring the mobile market the DirectX 8.1 compatibility that it had longed for.
In some instances, such as Unreal Tournament 2003, the pixel and vertex shader support means that games will run smoother (since complex rendering functions are replaced with a more simple vertex and/or pixel shaders). In other instances, the lack of DX 8 functionality means the difference between being able to play a game and not being able to play it. Although there are still a limited number of games that require full DirectX 8 compatibility, support for the API is becoming less of a luxury and more of a requirement a little over a year after its launch.
Longevity of a graphics chip is especially important in the mobile world, where getting a new GPU requires getting a new system. Therefore the inclusion of DirectX 8.1 pixel and vertex shaders is a huge advantage for the Mobility Radeon 9000 as it means that the chip should be able to play the games of today as well as tomorrow. And don't fool yourself: pixel and vertex shaders will soon find their way into OpenGL games as well.