PowerBook, iBook: Processor Cycling

This article defines processor cycling, tells how to turn it off, and explains its effect on a computer.

Products Affected

PowerBook, iBook

This article has been archived and is no longer updated by Apple.
Processor Cycling Defined

Processor cycling is an energy-saving feature built into PowerBook and iBook computers. It increases battery life by slowing down the processor when the computer is not being used. Processor cycling slows the processor to approximately 25 percent of its normal speed.

Turning off Processor Cycling

PowerBook and iBook computers come with processor cycling turned on when running on battery power. You can disable processor cycling by following these steps:


    1. Open the Energy Saver control panel.

    2. Click Advanced Settings.

    3. Click the checkbox to deselect the "Allow processor cycling" option.


There are certain events that prevent processor cycling from working, even when it is enabled:
  • moving the mouse
  • typing on the keyboard
  • saving or reading files on the hard disk
  • reading a CD-ROM or DVD-ROM disc

Side Effects

If a program is running and you're not using the mouse, keyboard, hard disk, or CD-ROM/DVD-ROM discs, processor cycling can cause the program to slow. For example, Macromedia Flash animations, which run entirely from RAM, may become choppy due to processor cycling.

Not helpful Somewhat helpful Helpful Very helpful Solved my problem