Memory configurations
Unlike discrete graphics cards, which offer only a handful of different memory configurations, ATI's Mobility Radeon 9600s are available with all sorts of different memory options. For starters, the chips come with either on-chip or off-chip memory, with the latter more appropriate for larger notebook form factors that have room for external memory chips. The Mobility Radeon 9600s support 32, 64, or 128MB of memory, and ATI claims it will be the first manufacturer to integrate 128MB of memory onto a graphics chip.

That ATI will be squeezing 128MB of memory onto a graphics chip the size of a postage stamp is impressive on its own, though versions of the chip with 128MB of integrated memory won't be available until the second half of 2003; ATI is waiting on memory chip volume.

Because the Mobility Radeon 9600s are meant for mobile applications where space is scarce, they're designed to work with a maximum of four memory chips. Unfortunately, this means that the chips have only a 128-bit memory bus, which will limit available memory bandwidth to some extent. The 256-bit memory bus featured in ATI's desktop Radeon 9700 and 9800s requires eight memory chips and there's just isn't enough room for that many chips in mobile form factors.

Though I've yet to receive confirmation from ATI, I would suspect that versions of the Mobility Radeon 9600 Pro that feature only 32MB of memory, a configuration that uses only two 16MB memory chips, will only be using half of the chip's 128-bit memory bus. A narrower memory bus will halve the Mobility Radeon 9600's available memory bandwidth in its 32MB configuration, but those concerned with 3D performance will likely opt for chips with more than 32MB of graphics memory, anyway.

Perhaps the most interesting thing about the Mobility Radeon 9600's available memory options is a new memory type that will be used in the Radeon 9600 Pro, GDDR2-M. GDDR2-M is a new memory standard designed specifically for mobile graphics applications with chips running at speeds between 300 and 450MHz DDR, effectively 600-900MHz. GDDR2-M uses a bus rather than a point-to-point interface, on-die termination, and promises lower power consumption than conventional memory chips. This new memory technology isn't unique to ATI or its Radeon 9600 Pro, so we may see other mobile graphics chipsets using GDDR2-M down the road.

Clock throttling to go
Since power consumption is such a big concern for laptops, at least those that won't always be tethered to a wall outlet, ATI's new Mobility Radeon 9600s feature a new version of ATI's POWERPLAY power management software. The appropriately-named POWERPLAY4 is ATI's fourth-generation power management system, and the refinement shows. Thanks to POWERPLAY4, the Mobility Radeon 9600s can run on as little as one or as many as 1.2 volts, depending on a user's needs. Here's how POWERPLAY4 does it:

• Core clock throttling - The key to POWERPLAY4's ability to conserve power is its control over the core clock speed and voltage of the Mobility Radeon 9600; POWERPLAY4 can dynamically dynamically adjust the clock speed and voltage of the graphics chip to meet an application's demands. When a user is working on the Windows desktop, running only 2D applications, the Mobility Radeon 9600's core clock speed and voltage will drop since there's really no need for the chip to be running at full speed for web surfing, word processing, or pretty much anything short of a 3D application. When POWERPLAY4 detects that a little extra juice is needed for something like Unreal Tournament 2003, it ramps up the graphics chip's clock speed and voltage accordingly.

  What triggers POWERPLAY4's core clock speed ramping? Use of the 3D pipeline, primarily. This means that any 3D application should cause clock speeds and voltages to increase. Some of the Mobility Radeon 9600s' multimedia features, including video de-blocking and MPEG encoding acceleration, may also be demanding enough, or use enough of the 3D pipeline to ramp up the chip's core clock speed.

• Memory clock throttling - Unfortunately, the Mobility Radeon 9600s' memory clock throttling isn't quite as fancy as what's possible with the chip's graphics core. It's not that ATI couldn't have the memory clocks changing dynamically based on an application's demands, but rather that adjusting the clock speed of the graphics memory creates a little bit of screen flicker that users aren't going to want to see all the time.

  Though screen flicker makes dynamic memory clock throttling undesirable, POWERPLAY4 can lower the graphics memory clock speed when a notebook is switched from A/C to battery power. When a notebook is switched over from A/C to battery power, the screen's brightness usually changes, so a brief flicker may even go unnoticed.

• Overdrive - POWERPLAY4's ability to dynamically change the Mobility Radeon 9600s' core clock speed is pretty neat from a power saving perspective because it allows the chip to run on lower voltages and consume less power. However, ATI has also leveraged this dynamic clock throttling technology to give the Mobility Radeon 9600s a bit of a performance boost where the chip's thermal environment permits. Since the Mobility Radeon 9600s will see action in a fairly wide range of notebook designs, some with better cooling than others, the chip's clock speed may end up being more limited by how robust a notebook's graphics chip cooling is rather than any sort of ceiling in the graphics core itself.

  Because ATI can't expect a near-silent 4lb notebook to keep the Mobility Radeon 9600s as cool as a 10lb portable gaming desknote, there's logic in the graphics core that senses the chip's thermal environment and ramps up the core clock speed where possible. This thermal environment-based ramping will scale the chip's core clock speed beyond its default speed, essentially overclocking the chip if the surrounding temperature is cool enough.

Overall, the Mobility Radeon 9600s' ability to throttle clock speeds when the graphics chip isn't being fully exploited should keep power consumption to a minimum without sacrificing performance. Clock-throttling to save power isn't new for mobile graphics chips, but Overdrive's ability to do a little automatic overclocking looks like a sweet bonus for notebooks with more robust cooling.