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.
