Apple Desktop Computer manual NanoKernel, Startup Disk Control Panel

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C H A P T E R 5

Software

variable-sized partitions that are used by Mac OS, Open Firmware, and any other client. PRAM resides in the Mac OS partition. The partitioning scheme is part of the CHRP specification.

NanoKernel

The previous version of the NanoKernel has code that is processor-specific to create data structures. Under NewWorld, the Trampoline code creates these data structures from information in the Open Firmware Device Tree.

NanoKernel is typically no longer changed to support a new CPU. Support for new processors has moved to POST, which is responsible for configuring all processor-specific registers. Run-time cache control is part of RTAS.

Startup Disk Control Panel

Open Firmware now bears responsibility for locating a startup device. This is very different from previous Mac OS systems where the Mac OS ROM had responsibility for locating the startup device. On the iMac computer, the Mac OS ROM image itself comes from the startup disk, so decisions regarding startup device must be made earlier in the startup process. Open Firmware recreates as much as possible the user experience of earlier systems but the implemention is very different.

Previous systems stored the user's selected startup device in PRAM. The startup device was set in PRAM when the user selected a device in the Startup Disk control panel. This device was honored by the Mac OS ROM unless the selected device was unavailable or was overridden by the user.

The startup disk routine for the iMac, rather than setting Mac OS PRAM, sets an Open Firmware config variable called boot-device. This setting is honored by Open Firmware unless the selected device was unavailable or was overridden by the user.

The following keys can be used to override the selected startup device.

■Key combination Command-Option-Shift-Delete: ignore the boot-device setting and scan for alternate devices.

■C key: force the internal CD-ROM drive to be the startup device

■D key: force the internal hard disk to be the startup device

66What Is Different

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Contents Apple iMac Computer Page Contents Devices and Ports RAM ExpansionSoftware RtasAppendix Abbreviations Index Rtas NV-RAMFigures and Tables Page Contents of This Note About This Developer NoteMac OS PowerPC G3 MicroprocessorSupplemental Reference Documents ATA DevicesUSB Devices Open FirmwareE F a C E Introduction Features Case and External Features Shows a front view of the computerFront view 2Side view showing I/O bay Compatibility Issues System SoftwareMain RAM Expansion Modules Video RAM Expansion ModulesUSB Ports and Devices Page Architecture Architecture Processor module G3 MicroprocessorBackside Cache Main Logic Board Memory Controller and PCI BridgeController IC USB Controller Video Display SubsystemBuilt-in Modem Infrared Link Module Devices and Ports USB Connectors USB PortsTransfer Types Supported GNDUSB Compatibility Issues ADB CompatibilityUSB Storage Devices Serial Port CompatibilityMacintosh-To-Macintosh Connections USB ControllerKeyboard Keyboard LayoutMouse Keyboard and USBHard Disk Drive Video DisplayInfrared Communication Link Sound SystemBuilt-in Microphone Sound InputsSound Outputs External Sound InputSound Specifications External Sound OutputHeadphone Jacks Total harmonic distortion Ethernet Port Internal ModemPage RAM Expansion Removing the Logic Board Assembly Expansion SlotsPlacing the Computer Face Down Removing the bottom cover Unfastening the CablesRAM Expansion 3Logic board assembly handle and retaining screws Removing the Retaining ScrewsRemoving the Logic Board Assembly Removing the EMI ShieldLocations of the Expansion Slots Main RAM Expansion 6Locations of the RAM expansion slotsMechanical Design of RAM SO-DIMMs Electrical Design of RAM SO-DIMMsSdram Devices Configuration of RAM SO-DIMMs RAM SO-DIMM Electrical Limits Address MultiplexingVideo RAM Expansion Page Software Why Make This Change? What Has Changed Features of the New Approach User Experience PerformanceRAM Footprint Data Structures and FilesBoot ROM Contents Mac OS ndrv Drivers RtasToolbox Image File Contents NewWorld Boot Process Trampoline CodeToolBox ROM Image What Is Different Interrupt HandlingOutmoded Resources RAM FootprintNanoKernel Startup Disk Control PanelOpen Firmware and the Device Tree Interrupt LayoutMachine Identification Software Abbreviations Chrp NMI Page Index Nvram X, Y, Z Allen Watson
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