Macintosh ROM Source Tree

This repository contains a fully commented, buildable 68000 assembly source tree for five classic-era Macintosh ROMs. The same source tree assembles into bit-identical copies of each ROM via --defsym ROM_TARGET={1..5}.

Legal disclaimer

This is a pure hobby project. No copyright infringements or similar is intended.
Please inform the author about possible legal issues before turning to a lawyer.

Build

Toolchain on Debian / Ubuntu:

sudo apt install binutils-m68k-linux-gnu

Build all five ROM variants and verify each against its reference binary:

make

The make step expects the reference binaries under the path given by the ROM_REF_DIR Makefile variable (default ../macroms/Mac_ROMs/68k). Override on the command line if needed:

make ROM_REF_DIR=/path/to/Mac_ROMs/68k

A successful run reports SUCCESS: ALL FIVE ROMS BIT-IDENTICAL.

You get these reference ROMs from here: https://www.macintoshrepository.org/7038-all-macintosh-roms-68k-ppc-

Per-target builds:

make mac_128k      # 1984-01, 64 KB,  $28BA61CE
make mac_512k      # 1984-10, 64 KB,  $28BA4E50
make mac_plus_v1   # 1986-01, 128 KB, $4D1EEEE1
make mac_plus_v2   # 1986-03, 128 KB, $4D1EEAE1  (branch-fix)
make mac_plus_v3   # 1986-03, 128 KB, $4D1F8172  (SCSI patch)

Layout

rom_original.s         Master include for Mac 128K / 512K
rom_plus.s             Master include for Mac Plus (all variants)
original/              Mac 128K / 512K source tree (5 subsystems)
plus/                  Mac Plus source tree (8 subsystems)
include/               Assembler equates (traps, low-mem, hw regs)
Makefile               Self-contained build pipeline

include/ files:

rom_target.inc         ROM target selector (MAC_128K..MAC_PLUS_V3)
traps.inc              287 A-line trap macros
lowmem.inc             386 low-memory globals
hwregs.inc             Hardware registers (VIA, SCC, IWM, SCSI)
sysequ.inc             System equates (IOParam, queues, events)
fsequ.inc              File system equates (VCB, FCB)
toolequ.inc            Toolbox equates (Window, Control, Menu, TE)
sonyequ.inc            Sony disk-driver equates
private.inc            Private system equates (memory mgr internals)
macros.inc             Helper macros (UNLINK, etc.)

ROM variants and checksums

Target	Date	Size	Checksum	Notes
mac_128k	1984-01	64 KB	28BA61CE	Original Mac
mac_512k	1984-10	64 KB	28BA4E50	"Fat Mac"
mac_plus_v1	1986-01	128 KB	4D1EEEE1	First Plus
mac_plus_v2	1986-03	128 KB	4D1EEAE1	Branch-condition fixes
mac_plus_v3	1986-03	128 KB	4D1F8172	SCSI patch (default)

The 128 K and 512 K Macs differ at only 6 sites totaling 57 bytes; all are wrapped in .if ROM_TARGET == MAC_128K / .else / .endif.

The three Plus variants differ at 6 sites totaling 33 bytes (v1->v3) or 31 bytes (v2->v3); all are wrapped in .if ROM_TARGET == MAC_PLUS_V<x>.

Source-tree organization

original/ (1984 ROM, ~38 files in 5 subsystems):

• boot/, os/, hw/, resources/, toolbox/

plus/ (1986 ROM, ~82 files in 8 subsystems):

• boot/, debugger/, extra/, hw/, os/, resources/, toolbox/ (with quickdraw/ sub-folder)

Each .s file begins with a banner describing its routines and any ROM-mandated cross-subsystem leakage. ROM byte order is fixed; the file-boundary placement reflects subsystem grouping where possible.

Acknowledgements

This repo builds on the massive amount of the work of others, last but not least by the team at Apple Computer Inc., who designed and implemented the Macintosh ROM.

A list of information sources that went into this project is provided below. It is likely incomplete - please open an issue if you find that a given resource missing.

• Inside Macintosh I-V
• https://www.gryphel.com/c/minivmac/index.html
• https://www.gryphel.com/c/minivmac/extras/fdisasm/c/index.html
• https://www.gryphel.com/c/minivmac/extras/fdisasm/c/roms.html
• https://www.gryphel.com/c/minivmac/appc/index.html
• https://web.archive.org/web/20230717141356/https://macgui.com/news/article.php?t=523
• https://web.archive.org/web/20230717144604/https://macgui.com/news/article.php?t=514
• https://web.archive.org/web/20230717142244/https://macgui.com/news/article.php?t=502
• https://web.archive.org/web/20230717150821/https://macgui.com/news/article.php?t=499
• https://web.archive.org/web/20231106024332/https://macgui.com/news/article.php?t=493
• https://web.archive.org/web/20230717142458/https://macgui.com/news/article.php?t=488
• https://web.archive.org/web/20230717142324/https://macgui.com/news/article.php?t=483
• https://web.archive.org/web/20230717141349/https://macgui.com/news/article.php?t=480
• https://web.archive.org/web/20230717142557/https://macgui.com/news/article.php?t=443
• https://web.archive.org/web/20230717142259/https://macgui.com/news/article.php?t=336
• https://web.archive.org/web/20230717141429/https://macgui.com/news/showcat.php?id=8
• https://www.bigmessowires.com/category/plustoo/
• https://www.pauladamsmith.com/blog/2025/09/classic-mac-patterns.html
• https://paulsmith.github.io/classic-mac-patterns/
• https://www.folklore.org/0-index.html
• https://axio.ms//projects/2024/06/16/MicroMac.html
• https://computerhistory.org/blog/macpaint-and-quickdraw-source-code/
• https://www.macintoshrepository.org/545-macintosh-programmer-s-workshop-mpw-3-x