Overview to the Single Processor Power Mac G5

The single processor, 64-bit desktop Power Mac G5 uses a PowerPC G5 processor and is intended for use in content creation, desktop publishing, multimedia, scientific and technical applications, and other activities that require high performance.

New Hardware Features

Here is a list of the new hardware features of the single processor Power Mac G5. A list of all hardware features is provided in Hardware Features Summary.

Hardware Features Summary

Here is a list of the hardware features of the single processor Power Mac G5. The major features are described more fully later in this note. To view technical Marketing documents, refer to http://www.apple.com/powermac/.

Features of the Enclosure

The single processor Power Mac G5 computer’s enclosure is a tower design. Figure 1-1 illustrates the front of the enclosure and Figure 1-2 illustrates the rear of the enclosure.

Figure 1-1  Single processor Power Mac G5 front view
Single processor Power Mac G5 front view
Figure 1-2  Single processor Power Mac G5 rear view
Single processor Power Mac G5 rear view

The enclosure has space for two hard disk drives and one optical device. See Hard Disk Drives.

To access the main logic board to install PCI cards or additional memory, refer to Expansion. For full details regarding opening and accessing the computer, refer to the Power Mac G5 User’s Guide that was shipped with your computer.

System Software

The single processor Power Mac G5 computer ships with Mac OS X 10.3.5 installed as the default operating system. The classic environment can be used to run Mac OS 9 applications. Install the Classic application from the “Additional Software and Apple Hardware Test” CD shipped with your computer.

To retrieve information from the I/O Registry, use the APIs in the header file IOKit/IOKitLib.h.

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 single processor Power Mac G5, the value of the model property is PowerMac9,1.

Power Management

The power management techniques implemented in the single processor Power Mac G5 are described in the following paragraphs.

Processor Power Step

To lower power consumption, heat generation, and fan noise, the single processor Power Mac G5 computer incorporates an automatic power management technique called power stepping. Power stepping 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. The stepped processor speed is either 900 MHz or 1.8 GHz. Switching between different processor/bus speeds and voltages is achieved by a very fast transition that is designed to minimally impact system or application performance and typically operates seamlessly to the user.

In addition, the single processor Power Mac G5 computer allows the user to control processor and bus. The options for specifying either high, reduced, or automatic processor and bus speeds are located at System Preferences>Energy Saver>Options; then select Automatic (default), Highest, or Reduced.

If the single processor Power Mac G5 computer detects a system temperature that is too high, due to high ambient temperatures or other factors, it will automatically reduce the processor and bus speeds to half speed, regardless of the selected setting. If the temperature continues to be too high, the system will enter sleep mode to prevent permanent damage.

Processor States

The following processor states are defined:

  • Run: The system is running at maximum processing capacity with the processor running at full speed.

  • Idle: The system is idling; this is the default state. All clocks are running and the system can return to running code within a few nanoseconds. If the system has no work to do, it will be in idle mode.

    From idle, the processor will enter deep nap state when the system is power-stepped to half frequency. In this state, the processor’s internal frequency is reduced to 1/64 of the maximum frequency. The processor frequency is returned to normal on exit from idle. The exit from idle takes a bit longer than the regular idle nap but is still in the nanoseconds.

System Modes

The Macintosh system has the following power-saving modes, which are set in the Energy Saver pane. If the system does not support full sleep, it will use the less efficient doze mode.

  • Run: The system is fully functional in normal operating mode with all components powered and operating.

  • Doze (default): The power to the disk drive motors and the display is turned off, but the power supply and fans are still on. PCI cards that don't support full system sleep (some SCSI cards, some graphics cards) will cause the machine to doze rather than fully sleep.

  • Full sleep: The main power supply is shut down. A trickle supply provides auxiliary power to the PCI slots and keeps the DRAM state preserved for a quick recovery. The processor is powered off with its state preserved in DRAM. All non-essential clocks in the system are suspended. This mode allows the computer to meet Energy Star sleep requirements while providing the ability to start up without rebooting. This system may be awakened by administrative network packets, keyboard or mouse activity, USB device insertion or removal, or SMU scheduled wakeup.

  • Off: The single processor Power Mac G5 meets FEMP (Federal Energy Management Program) requirements and supports FireWire ports functioning as repeaters when operating on AC power.

Velocity Engine Acceleration

The Velocity Engine is the vector processing unit in the PowerPC G5 microprocessor. System software has been modified to take advantage of the accelerated processing that the Velocity Engine makes possible and to support low-level operations using the Velocity Engine.

For complete information on the Velocity Engine, refer to the following Apple website:

http://developer.apple.com/hardwaredrivers/ve/index.html