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Desktop Graphics Ambitions: ATi Mobile Radeon 9800

The MR 9800's Details Spell The End Of The AGP Line, Continued

However, the power consumption of the MR9800 is, according to the manufacturer's statements, about 30% to 40% above that of the MR9700 - despite the fact that the clock speed of the core is considerably lower at 350 MHz than that of its predecessor (445 MHz). But with 110 million transistors, the number of transistors is significantly higher. After all, additional power is needed to operate twice as many pixel pipelines and vertex shader units.

To keep the MR9800's thirst for energy within bounds, however, the chip uses the "Powerplay" power-saving techniques, which its predecessors, the MR9600 and the MR9700, also utilize. Examples of these functions are "Power on demand" or "Clock Gating".

While the first technique automatically and dynamically controls the clock rate of the core according to the load on the graphics subsystem, clock gating is used to switch off function blocks of the chip that are not being used at the moment - or switched on again when they are needed (see the blocks outlined in red in the illustration below).

Aggressive clock gating allows the function blocks of the graphics core to switch on and off automatically depending on demand, thus saving energy.

In addition, the user has the option of reducing the clock rates of the core and the memory by means of a graphical user interface, thereby increasing battery life.

In the case of many graphics card drivers, this GUI can be used to set the clock rates of the graphics core and the video memory to one of three levels.

But not every notebook manufacturer offers this feature with the graphics card driver. Of our two test devices, only the Dell Inspiron 9100 had this feature. The connection between the setting and the clock speeds in this device is as follows:

It goes without saying that the frame rate in 3D games will be lower with lower clock speeds. We also tested the extent to which the lower speed of core and video memory affects battery life.