A portable, software-controlled system for managing power consumption in a computer system. The power management system is integrated with the operating system of the computer system and is extensible to any add-on devices that are installed into the computer system. Upon the detection of a power down condition indicating that the computer system should be powered down, the power management system may verify that the computer system can be powered down without causing any of the devices that are connected to the computer to lose application data. If all of the devices agree that the computer system can be powered down, then each device has its state saved into memory and is powered down. Next, the state of each processor is saved into memory and power to the processors is disabled. In order to suspend the computer system, power to the memory is maintained, allowing each device state and processor state to be restored upon reboot. The computer system may be hibernated by writing all of the active memory (including each device state and processor state) to a secondary storage area and then powering off the entire computer system, including memory.