Technical information

CHAPTER 5
System Software
78 The New Approach
Most of the changes are completely transparent to the Mac OS. Only the Startup
Disk control panel is affected: it includes added code to modify the Open
Firmware’s configuration variables in the NV-RAM.
Features of the New Approach 5
Because the 1999 PowerBook G3 Series computer has new hardware features
that are different from other PowerBook computers, new software features are
needed in addition to the NewWorld requirements for other computers. This
list includes features that implement the NewWorld approach along with
features that support the new hardware features:
■ 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 operating system
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 operating system 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 high-level software that resides
in the Mac OS 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.
Performance 5
Performance of a 1999 PowerBook G3 Series computer using ROM in RAM
should exceed performance measurements for other Macintosh computers with