Specifications

Computer Identification

Rather than reading the box flag or the model string and then making assumptions about the computer’s

features, applications that need to find out the features of the computer should use I/O Registry calls to test

for the features they require.

Asset management software that reports the kind of computer it is run on can obtain the value of the property

at Devices:device-tree:compatible in the IODeviceTree plane of the I/O Registry. The model string is

the first program-usable string in the array of C strings in the compatible field. For the Power Mac G5 2.0

GHz and 2.3 GHz configurations, the value of the model property is PowerMac7,2 ; the 2.7 GHz configuration

model property value is PowerMac7,3 .

Note: To differentiate these models of the Power Mac G5 from previous versions, look at the EMC

number on the label on the back of the computer. This developer note addresses EMC number 2061.

Power Management

The basics of Power Mac G5’s power management techniques are described in the following paragraphs.

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/bus speeds and high voltage when the demand on the processor is high, and to run at low

processor/bus speeds and low voltage when the demand on the processor is low.

Note: The memory bus runs at 400 MHz and does not slew.

Switching between different processor/bus speeds and voltages is achieved by a gradual transition that is

designed to minimally impact system or application performance and typically 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:

Processor rangeConfiguration

1.8 GHz to 2.0 GHz2.0 GHz

1.8 GHz to 2.3 GHz2.3 GHz

2.0 GHz to 2.7 GHz2.7 GHz

Overview to the Power Mac G5

System Software