Power Saving Modes

The current Power Manager, version 2.0, is a native Mac OS manager designed to implement a common power management strategy across all Macintosh models.

Processor States

The following processor states are defined:

Run Multiple: The system is running at maximum processing capacity. In a single processor system the processor is running at full speed. In a multi-processor system all processors are running at full speed.
Run Single: One processor is running at maximum processing capacity. In a single processor system, this is the same as Run Multiple. In a multi-processor system, only one processor is running at full speed; all other processors are in sleep mode with their caches flushed and their states saved.
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. In a multi-processor system, all other processors will be sleeping as described in Run Single.
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 flushed, 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 flush on entry. In a multi-processor system, the other processors will be sleeping as described in Run Single.

System Modes

The Macintosh system has two power saving modes.

Doze: The power to the disk drive motors and the display is turned off, but the power supply and fan are still on. The computer can still respond to network activity.
Sleep: The main power supply is shut down. A trickle supply provides auxiliary power to the PCI slots and keeps the DRAM state preserved for a 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. This mode allows the computer to meet the 5W sleep requirement while providing the ability to start up without rebooting.