Processor and Bus Slewing

To lower power consumption, heat generation, and fan noise, the Power Mac G5 computer incorporates an automatic power management technique called bus slewing. Bus slewing is designed to run at high processor and bus speeds and high voltage when the demand on the processor is high, and to run at low processor and bus speeds and low voltage when the demand on the processor is low. Switching between different processor/bus speeds and voltages is achieved by a gradual transition that does not impact system or application performance and operates seamlessly to the user. In slewing, the bus runs at half the speed of the processor.

The ranges of the slewed processor speeds are listed below:


Configuration
Processor range

1.6 GHz
1.3 GHz to 1.6 GHz

1.8 GHz
1.3 GHz to 1.8 GHz

2.0 GHz
1.3 GHz to 2.0 GHz


In addition, the Power Mac G5 computer 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>Options; then select Automatic, Highest, or Reduced.

If the Power Mac G5 computer detects a system temperature that is too high, due to high ambient temperatures or other factors, it will automatically enter bus slewing mode regardless of the selected setting.”

My bet is that the machine comes set at “Automatic”. The question then becomes how many of the benchmark results we’ve been seeing have been influenced by this setting. If I get a chance to re-run my benchmarking tests with the G5’s set at Highest, I’ll add a section to the ComputerZone showing the results