ATI Rage Mobility 128

Dual Display

Much like the Matrox G400's Dual Head feature, the Mobility 128 is capable of driving two different displays with different content on each or the same content as desired. One display will of course be the notebook's built-in flat panel, but the other can be the TV-out, an external analog monitor, or even an external DVI flat panel. Whether or not we see any OEM's actually implement a DVI interface is up to them, but the Mobility 128 does make the option available.

Available resolutions are limited only by the available frame buffer and with 8MB of external frame buffer, for a total of 16MB, two 1600x1200 displays in 2D are possible. One of the displays is capable of running in 3D, but not both. Interestingly, ATI is pushing a new resolution that we haven't seen before - 1400x1050 - that slots right between 1280x1024 and 1600x1200. They believe that this will become the new standard for high res 15" panels.

As mentioned previously, no additional hardware beyond connectors and support on the PCB are required for these features - it's all built into the single chip Mobility 128. Dual display is accomplished through Windows 98's support for multi-monitor setups, so it won't work under NT4. However, once drivers are developed for Windows 2000, it should work there as well. Dual display was also available in ATI's original Rage Mobility chip.

Filtered Ratiometric Expansion

"Filtered Ratiometric Expansion" is a big fancy term that sounds a lot more complicated than it really is. At least the concept is easy, while the implementation certainly isn't - just ask the ATI engineer that had to do it ;)

You may have noticed that most notebooks out there don't handle resolutions other than the flat panel's native resolution very well. Either the image will only take up part of the screen or a low quality scaling job will be applied to the display which results in extremely jagged output. This is because, unlike a conventional CRT monitor, flat panel displays have a fixed number of pixels that are addressed individually.

For the most part, this isn't a huge deal since it usually makes the most sense to run your notebook at its native resolution anyway. The problem crops up the most in full screen DOS sessions or in games, but can also be seen during the Windows 98 boot screen and sometimes the BIOS screen.

ATI's solution is filtered ratiometric expansion, which basically means that it takes a low res image and scales it cleanly up to the native resolution of the panel you're using. However, the key is that it scales it smoothly through filtering. It's similar to the filtering a 3D accelerated uses to prevent pixelation when you walk right up to a wall or that most graphics cards do when you playback a movie full screen. The Mobility 128 is capable of scaling resolutions up to 1280x1024 to the panel's native resolution (for panels up to 1600x1200).

Since we were testing on a desktop platform with an analog monitor, we were unable to explore this features. The Rage Mobility also has this feature and feedback from owners of such notebooks has generally been positive. ATI claims that since it is implemented in hardware, there is currently only a 2-3% performance drop when it is enabled while playing games or watching a DVD movie. While 3-4% certainly isn't much, the good news is that ATI expects this to drop to 0% in future revisions of the chipset.