Chapter 8: Power Management

Chapter 8

Power Management

Technophobes may take solace in the fact that they retain ultimate control over their electronic servants so long as they control the power switch. Power is, of course, the sine qua non of computing, but personal computers haven t done an especially good job of managing it until quite recently.

More effective power management is important for at least three reasons. First, as a matter of sound ecology, using less power helps minimize the impact of computing on the environment. Not only do computers require power, but so do the air-conditioning systems for the rooms where the computers reside. A second reason better power management is needed is familiar to many travelers: battery technology simply hasn t kept pace with the demand for mobile computing of all kinds. And finally, greater consumer acceptance of PCs as home appliances depends on improving power management. Current machines have noisy fans and squealing disk drives when they re on, and they take a long time to start up from the power-off state. Decreasing the power-up latency and eliminating unnecessary noise which also means minimizing power consumption so that less cooling is required will be necessary before PCs can comfortably occupy consumer niches.

In this chapter, I ll discuss the role WDM drivers play in power management in the MicrosoftWindows XP and Microsoft Windows 98/Me operating systems. The first major section of the chapter, The WDM Power Model, presents an overview of the concepts you need to know about. The second section, Managing Power Transitions, is the meat of the chapter: I ll describe there the very complicated tasks a typical function driver carries out. I ll finish the chapter with a discussion of some ancillary responsibilities a WDM function driver has with respect to power management.