PATHHardware Documentation > iBook Developer Note

Power Saving Modes

The iBook meets the following energy saving standards:

Energy Saver
Energy Star (US)

To meet those standards, the default configuration of the computer must draw less than 7 watts in Sleep mode and less than 5 watts in off mode, while plugged into the AC adapter and with the battery removed.

The power manager has been redesigned to reduce power consumption in Sleep mode. The new version, Power Manager 2.0, is a native Mac OS manager designed to implement common power management policy across all Macintosh models by means of the new Power Plugin component.

With the new power management architecture, the following operating modes are defined:

Run Single: One processor is running at maximum processing capacity.
Idle One: The system is idling. All clocks are running and the system can return to running code within a few nanoseconds. In a single processor system, the main processor is stopped in DOZE mode. Cache coherency is maintained in this level of idle.
Idle Two: The system is in power saving mode. This mode is entered only when a system has been in Idle one state for a substantial period of time (a half second or so) with no activity. In a single processor system, the main processor cache is ushed, and the processor is put into sleep mode--the external processor bus clock is stopped. The delay in coming out of this state is on the order of a millisecond. Cache coherency is maintained by the ush on entry.
Sleep: The system is completely shut down, with only the DRAM state preserved for quick recovery. All processors are powered off with their state preserved in DRAM. All clocks in the system are suspended except for the 32.768Khz timebase crystal on the PMU99 IC.

The computer automatically enters Idle mode after several seconds of inactivity. This mode easily meets the requirement of less than 7 watts of power consumption. While the computer is in Idle mode, if it is attached to a network, it is able to respond to service requests and other events directed to the computer.

Idle mode is not the same as Sleep mode. The computer cannot respond to network activity when it is in Sleep mode. To prevent the computer from going into Sleep mode, the Sleep setting in the Energy Saver control panel must be set to "Never."

Although the current public Power Manager interfaces will be maintained for application compatibility, this is a major revision that may affect developers. Information about the API changes for Power Manager 2.0 is available in a technote, which can be obtained from the web site at

http://developer.apple.com/technotes/