In an attempt to standardize (read: abstract) the various approaches to power management, Microsoft developed the OnNow Initiative. This specification builds on the capabilities of the hardware, providing a common platform for the various Microsoft operating systems to exploit.
The OnNow initiative abstracts the power management capabilities of the system (mainboard) and devices. While individual devices may incorporate many clever powering schemes, the OnNow model describes distinct power states that a device or system can occupy at any given time.
A system exists in one of six power states, designated S0 through S5. The meanings are described in Table 10.1. The overall state of the system largely restricts the ...