Editing Macintosh Old World ROM (section)

== Technical Specifications ==

=== ROM Addressing ===
Old World ROM systems map ROM at specific addresses:

'''68k Systems:'''
* '''Physical location''': Typically $400000-$4FFFFF (varies by size)
* '''Boot overlay''': ROM temporarily mapped to $000000 during POST
* '''Vector table''': Exception vectors copied from ROM to RAM

'''PowerPC Systems:'''
* '''Physical location''': $FFC00000-$FFFFFFFF (4MB window)
* '''Exception vectors''': PowerPC vectors at $FFF00000
* '''68k emulation space''': Virtual 68k addresses mapped by emulator

=== Performance Characteristics ===
ROM access speeds varied by generation:
* '''68000-68020''': 150-250ns ROM chips, no wait states
* '''68030-68040''': 120-150ns ROM, possible cache hits
* '''PowerPC 601-604''': 70-120ns ROM, instruction cache crucial
* '''PowerPC G3''': 60-70ns ROM, large L2 cache mitigates slow ROM