Overview of the iMac G5
This chapter provides an overview of the hardware and software features of the current models of the iMac G5.
In this section:
Feature Set
Below is a list of the features of the iMac G5. Each feature is described in more detail in a later section and the various configurations are summarized in Table 1-1.
Processor speed: The microprocessor in the iMac G5 is a PowerPC G5 with a clock speed of 1.6 GHz or 1.8 GHz. For more information, see “PowerPC G5 Microprocessor.”
Processor system bus:The processor interface system bus runs at one-third the speed of the system processor. For more information, see “Memory Controller.”
Cache: The backside 512 KB L2 cache is included on the microprocessor IC and has the same clock speed as the microprocessor.
Memory: The computer comes with 256 MB of DDR400 (PC3200) SDRAM installed in one 184-pin DIMM expansion slot; a second slot is available for expansion. The maximum supported memory is 2 GB. For more information, see “Main Memory Bus.”
Hard disk storage: The education configuration has a 5400 rpm, built-in UATA/100 hard disk with a capacity of 40 GB. The retail configurations have a 7200 rpm, built-in Serial ATA (SATA) hard disk with a capacity of 80 GB or 160 GB with a build-to-order option of 250 GB. For more information, see “Hard Disk Drive.”
SuperDrive: The 20” configuration and some 17” configurations of the iMac G5 have a SuperDrive. The education configuration does not have an optical drive. For more information, see “SuperDrive.”
Combo drive: One 17” configuration of the iMac G5 have a combination CD-RW/DVD-ROM drive. The education configuration does not have an optical drive. For more information, see “Combo Drive.”
Display: The iMac G5 has a built-in 20-inch widescreen flat-panel or a 17-inch widescreen flat-panel (measured diagonally). For more information, see “Flat Panel Display.”
USB 2.0 ports: The computer has three USB 2.0 ports; see “PCI USB Controller.”
Graphics acceleration: The computer has an AGP 3.0 8x accelerated graphics IC installed. For more information, see “Accelerated Graphics Port Bus.”
Graphics IC: The retail configurations have the NVIDIA GeForce FX 5200 Ultra with 64 MB RAM; the education configuration has the NVIDIA GeForce4 MX with 32 MB RAM. For more information, see “Graphics ICs.”
External video port: The external display connector supports VGA, composite and S-video formats for devices such as monitors, projectors, and television sets. Available separately are the Apple VGA adapter to connect with a VGA display and a video adapter with composite and S-video connectors. For more information, see “Video Monitor Port.”
FireWire 400 ports: The iMac G5 has two IEEE-1394a FireWire 400 ports, which support transfer rates of 100, 200, and 400 Mbps. For more information, see “FireWire 400 Connector.”
Target disk mode: The computer can be configured like a FireWire storage device connected to another computer. See “Target Disk Mode.”
Modem: The retail configurations of the computer have a built-in 56 Kbps modem supporting K56flex, V.90, and V.92 modem standards. The education configuration does not have a modem. For more information, see “Internal Modem.”
Ethernet: The iMac G5 has a built in Ethernet port for a 10Base-T and 100Base-TX operation. For more information, see “Ethernet Port.”
AirPort Extreme (optional): A 54 Mbps AirPort Extreme Card is available as a build-to-order option or as a user-installable upgrade. For more information, see “Wireless LAN Module.”
Bluetooth (optional): Fully-integrated Bluetooth is available as a build-to-order option to enable short-range wireless connections between desktop and laptop computers and a host of other peripheral devices. For more information, see “Bluetooth Technology.”
Sound: The iMac G5 includes built-in stereo speakers and microphone, combination stereo headphone jack and S/PDIF output jack, and analog audio line-in. For more information, see “Sound System Overview.”
Keyboard: The iMac G5 comes with an Apple Keyboard. The keyboard is also a USB hub with two USB 1.1 ports. For more information, see “Keyboard Features.”
Mouse: The iMac G5 comes with an Apple Mouse, a USB mouse with optical tracking. For more information, see “Mouse.”
Energy saving: Processor performance can be set to automatic (default), highest, or reduced via the Energy Saver pane in System Preferences.
Energy saving: The system can be set to go to sleep at a determined idle time.
Wireless keyboard and mouse: The Apple wireless keyboard and mouse are available as build-to-order options and require built-in Bluetooth.
Configuration Summary
The table below summarizes the main features of the iMac G5 features.
System Software
The iMac G5 comes with Mac OS X version 10.3.5 installed. The classic environment can be used to run Mac OS 9 applications. Install the Classic application from the “Additional Hardware and Apple Software Test” CD shipped with your computer. For more information about Mac OS X, see the reference listed in “Mac OS X.”
Machine Identification
Apple Computer discourages the targeting of code to specific machine models. However, if it is necessary to identify a machine in order to determine the features of the machine, applications can use the IORegistry with Mac OS X. Or, in many cases, it is feasible to use Gestalt calls to test a machine for specific features.
Asset management software that reports the kind of machine it is run on can obtain the value of the property at Devices:device-tree:compatible in the IODeviceTree Plane of the IO Registry. The model string is the first program-usable string in the array of C strings in the compatible field. The value of the string in the compatible property is PowerMac8,1.
The string obtained from the compatible property cannot be displayed to the computer user. If it is available, use the result from calling Gestalt ('mnam', &result) where result is a string pointer. This call returns a Pascal style string that can be displayed to the user.
Power Management
The power management techniques implemented in the iMac G5 are described in the following paragraphs.
Processor Power Step
To lower power consumption, the iMac 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 for the 1.8 GHz processor or 800 MHz or 1.6 GHz for the 1.6 GHz processor. 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 iMac G5 computer allows the user to control speed of the 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.
Note: For best performance when using professional applications with high demand on the system (such as Final Cut Pro or Logic), you may want to set the processor/bus speed option to highest.
If the iMac 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 speed regardless of the selected setting. If the temperature continues to be too high, the operating system will cause the system to enter sleep mode.
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.
Full sleep: The main power supply is shut down. A trickle supply provides auxiliary power 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 iMac 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 (an implementation of AltiVec) is the vector processing unit in the PowerPC G5 microprocessor. Some system software has been modified to take advantage of the accelerated processing that the Velocity Engine makes possible. System software has also been modified 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
For more information, please see the references at “Velocity Engine.”
© 2000, 2007 Apple Inc. All Rights Reserved. (Last updated: 2007-04-03)