6. Nvidia's PowerMizer: PowerNow For The GPU

The maximum power consumption of a GPU, even when in full 3D operation, is much lower than that of the CPU - approximately 2.5 W, as opposed to 35 W. However, designers are leaving no stone unturned in their efforts to increase battery life, and have now devised an ingenious power-saving mechanism for GPUs, too. It is being marketed under the name PowerMizer. PowerMizer works in a similar way to PowerNow. Certain sections of the GPU may be enabled or disabled, depending on the performance requirements of the application, and the clock speed of the GPU and the video memory can be altered dynamically. So, when playing a DVD, the Geforce4 420 Go only consumes 1.2 to 1.4 W (manufacturerÆs figures), even though it is hard at work with iDCT, motion compensation, color space conversion and video scaling.

In addition to "automatic battery-saving," the PowerMizer also provides the option of limiting the maximum clock frequency. These adjustments can be made in the PowerMizer section of the driver.

The PowerMizer GUI.

Effects of PowerMizer on GPU and Memory Clocking.

By moving the adjuster, the user can choose maximum performance at the expense of battery life or maximum battery life at the expense of performance (lower frame and fill rates).

Nvidia claims that its system can reduce overall power consumption by as much as 25%, although this calculation is based on 3-D scene rendering, a task where the GPU assumes a good deal of the CPU load. The maximum power savings that can be achieved through PowerMizer depend not only on the application being used, but also on screen size and brightness. Our measurements later in this article show whether, and to what extent, these mechanisms can extend battery life for the normal user.