6. Persuading Mobile CPUs To Conserve Energy

Windows allows users to adjust CPUs' use and power savings. The interface for such controls appears under the Power Schemes tab in the Power Options section in Control Panel.

Windows XP gives users various ways to control CPU behavior.

The following table presents an overview of how the individual settings work on CPU clock rates, and thus also exert an indirect influence on energy consumption and battery lifetime.

Windows XP Power Schemes Operating mode: AC Power
Name of power scheme	Clock control	Clock rate
Home/Office Desktop	fixed	(1860 MHz)
Portabel Laptop	adaptive	(800 <> 1860 MHz)
Presentation	adaptive	(800 <> 1860 MHz)
Always on	fixed	(1860 MHz)
Minimal Power Management	adaptive	(800 <> 1860 MHz)
Maximum Battery	adaptive	(800 <> 1860 MHz)
Operating mode: Battery
Name of power scheme	Clock control	Clock rate
Home/Office Desktop	adaptive	(800 <> 1860 MHz)
Portable Laptop	adaptive	(800 <> 1860 MHz)
Presentation	Degrade	(800 MHz)
Always on	fixed	(1860 MHz)
Minimal Power Management	adaptive	(800 <> 1860 MHz)
Maximum Battery	Degrade	(800 MHz)

Overview of the effects of various power schemes when operating from AC power or the battery using the Pentium M750 as an example.

We assume that the user has the option to choose if the CPU runs with:

A fixed maximum clock rate A fixed minimum clock rate, or Automatic, dynamic adjustment of the clock rate to meet current demand.