The hardware that makes up today’s laptops has gotten quite efficient and we have worked hard to improve Windows' ability to manage that hardware. One of the biggest improvements in the mobile PC experience for Windows since the early 1990 is longer battery life. The trick here is to make the system as efficient as possible while still maintaining a great user experience. At the same time, the increased cost of electricity has become a key factor for enterprise customers who are under continued pressure to manage TCO (total cost of ownership). As a result of all of these factors, we decided to make some extensive changes in the power management sub-system for Windows Vista.

The Windows Vista power management goals were simple: 1) making turning a computer "off"/"on" as reliable, simple, and fast as turning off/on a TV, and 2) maximizing the active usage if on battery and reducing the energy consumption if on A/C power. The first goal involved not only improving the predictability of the behavior when a PC was switched "off", but more importantly changing the model for what "off" and "on" means. Everyone knows that turning a TV off doesn’t really turn it off. It is still available to receive the remote control signal, etc. so that it can come back on quickly. We wanted to emulate this for Windows Vista machines.(continue at source)