Editing Macintosh Old World ROM (section)

=== ROM Organization and Contents ===
The Old World ROM contains several critical components that define the Macintosh computing experience:

'''Core Components:'''
* '''[[Macintosh Toolbox]]''' routines: QuickDraw graphics engine, Window Manager, Menu Manager, Event Manager, Resource Manager, and other GUI managers
* '''Hardware initialization code''': CPU configuration, memory controller setup, bus initialization
* '''POST diagnostics''': Power-On Self-Test routines for memory, ROM checksum, and basic hardware verification
* '''Boot loader code''': Device enumeration and System Folder location routines
* '''68LC040 emulator''' (PowerPC models): Nanokernel providing transparent 68k compatibility

The ROM size evolved significantly across generations:
* '''64 KB''' - Macintosh 128K/512K (1984)
* '''128 KB''' - Macintosh Plus (1986)
* '''256 KB''' - Macintosh SE, II series (1987)
* '''512 KB''' - Macintosh IIci, IIfx (1989)
* '''1 MB''' - Quadra series (1991)
* '''4 MB''' - Power Macintosh (1994)