Apple Desktop Computer manual Features of the New Approach

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C H A P T E R 5

Software

Features of the New Approach

Because the iMac has new hardware features that are different from other Macintosh computers, new software features are needed in addition to the NewWorld requirements for other Macintosh computers. This list includes features that implement the NewWorld approach along with features that support the new hardware features of the iMac computer.

■Power-on Self Test (POST) software, which resides in the Boot ROM, provides hardware initialization and diagnostic functions.

■Open Firmware, which resides in ROM, completes hardware initialization, provides a description of the hardware, loads initial OS software, and transfers control to that software.

■Run-Time Abstraction Services (RTAS), which resides in ROM, is instantiated into RAM through an Open Firmware method called by the OS. RTAS provides functions that are available to the OS at any time to access platform-specific hardware, such as the real-time clock and NV-RAM.

■Mac OS ROM image, a file that contains the ToolBox ROM code and other high-level software that resides in the ToolBox ROM on other Macintosh computers.

■10Base-T/100Base-TX Ethernet device driver, in the Boot ROM.

■Device driver for the USB hub, Apple USB keyboard, and Apple USB mouse, in the Mac OS ROM image.

In addition to the above new features, changes have been made to the source base for the components of the Mac OS ROM to abstract it from the hardware. These changes are designed to reduce bring-up time and effort, improve reliability of the Mac OS ROM components, and reduce testing time, by moving the changes necessary for a new computer to the Boot ROM. Some of the hardware components accessed through this new abstracted software are the interrupt controller, ADB, USB, SCSI, ATA (IDE), sound, and Ethernet.

The NewWorld architecture has a ToolBox ROM image that is high-level enough to be used on many different Macintosh computers. Although the iMac is the first Macintosh computer to use it, this new architecture is intended for use on all future Macintosh computers.

58Why Make This Change?

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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 SoftwareVideo RAM Expansion Modules Main RAM Expansion ModulesUSB Ports and Devices Page Architecture Architecture G3 Microprocessor Processor moduleBackside Cache Memory Controller and PCI Bridge Main Logic BoardController IC Video Display Subsystem USB ControllerBuilt-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 InputExternal Sound Output Sound SpecificationsHeadphone Jacks Total harmonic distortion Ethernet Port Internal ModemPage RAM Expansion Expansion Slots Removing the Logic Board AssemblyPlacing 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 Trampoline Code NewWorld Boot ProcessToolBox ROM Image What Is Different Interrupt HandlingOutmoded Resources RAM FootprintNanoKernel Startup Disk Control PanelInterrupt Layout Open Firmware and the Device TreeMachine Identification Software Abbreviations Chrp NMI Page Index Nvram X, Y, Z Allen Watson
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