From the devnote:
http://developer.apple.com/documenta...ion/index.html
"Processor and Bus Slewing
To lower power consumption and heat generation, the 15-inch PowerBook G4 incorporates an automatic power management technique called bus slewing. Bus slewing is designed to run at high processor speed, bus speeds, and voltage when the demand on the processor is high, and to run at low processor speed, bus speeds, and voltage when the demand on the processor is low. Switching between different processor/bus speeds and voltages is achieved by a transition that operates seamlessly to the user and should not impact system or application performance.
The 15-inch PowerBook G4 allows the user to control bus slewing mode. The options for specifying either high, reduced, or automatic processor and bus speeds are located at System Preferences>Energy Saver>Show Details>Options>Processor Performance; then select Automatic, Highest, or Reduced.
Slewing is enabled with the automatic setting. When the 15-inch PowerBook G4 is operating on AC power, the default is highest; when operating on battery power, the default is automatic.
If the 15-inch PowerBook G4 detects a system temperature that is too high, due to high ambient temperatures or other factors, it will automatically force the system to slew regardless of the selected setting.
When the 15-inch PowerBook G4 is in slewing mode, the processor, processor bus, and memory bus dynamically adjust their speeds based on the current needs of the system. In the 1.0 GHz configuration, the processor speed will switch between 1 GHz and 612 MHz. In the 1.25 GHz configuration, the processor speed will switch between 1.25 GHz and 765 MHz. For both configurations, the processor bus and memory bus will switch between 167 MHz and 102 MHz."
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