Apple iMac G5, 20-inch - Manual (Page 251)

iMac G5, 20-inch Troubleshooting - 27 SMU Button
SMU Button
The iMac G5 uses an advanced system management unit (SMU) to manage the thermal
and wattage conditions, while keeping the acoustic noise to a minimum. The SMU controls
the fans and regulates the speeds to run each fan.
The SMU reset button (shown below) is similar to the PMU button on previous iMac
computers.
The SMU supports the following functions:
• provides initial configuration of system clocks
• automatically initiates and sequences voltage and frequency slews when the OS
requests a transition to a new run level
• handles all power button and environmental user events
• controls RPM fans
• provides processor Mode Ring and thermal data store
• monitors processor temperature and power consumption
• monitors VRD10-compliant processor power supply digital interface.
The iMac G5 system employs advanced thermal and wattage management to keep
acoustic noise to a minimum. The enclosure is divided into discrete zones, each with
independently controlled fans bringing in cool air from the front of the enclosure, directing
it over system components and exhausting it out the rear. Temperature and power