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Mac ROM-inator II Programming

Programmer software
With the BMOW SIMM programmer, the Mac ROM-inator II’s flash memory can be reprogrammed, providing the ultimate in customization. There’s several megabytes of total flash memory available depending on the SIMM version, usable for any purpose like a new ROM disk image, alternate ROM code, or other crazy experiments. Using compression, this is enough for the base 512KB ROM image plus a disk image of 2 to 10 megabytes. Or fill the whole space with a collection of different base ROMs, selected from a startup menu. Go nuts!

The ROM-inator II is based on Doug Brown’s original Mac ROM SIMM design, used with permission.

As of February 2019, the ROM-inator II SIMM programmer from BMOW has been discontinued. Sorry! Experts can build their own compatible dougg3 programmer. Also check out the CayMac Vintage ROM SIMM programmer.



The programmer is a USB peripheral, and connects to your PC with a standard USB B Mini cable. The programmer utility software provides an easy GUI for updating the contents of the ROM SIMM’s flash memory. The utility program is compatible with Windows 7 or later, or Mac OSX, and you can also make it work on Linux if you compile the software for yourself. It’s based on Qt and should be easily portable.

The flash memory available for programming depends on the ROM-inator version:

Version Flash Compressed Disk Size
Atom 2 MB 2.2 MB
Basic 4 MB 5.5 MB
Mega 8 MB 12 MB

The programmer board has an integrated on/off switch for convenience. Please connect the USB cable and insert the SIMM into the socket before switching the power on. Hot-plugging the ROM SIMM or the programmer itself may cause damage.

Creating a New ROM Disk

Don’t like the contents of the default ROM disk, and want to use your own? No problem. Create a bootable HFS disk image that’s 2.2MB (5.5MB for the Basic, 12MB for the Mega) and fill it with whatever system software and other goodies you’d like. Then use the ROM SIMM Programmer to write a modified ROM and ROM disk to the Mac ROM-inator II SIMM. See the ROM disk creation tutorial for complete details.

Advanced Hacking


Interested in alternative happy mac icons? Fancy a shot at reverse-engineering? How are your 68000 assembly skills? For true power users, all this and more is possible by patching the base ROM. Check out this ROM Hacking Tutorial for an example of modifying the startup sound behavior in the Mac’s base ROM code. Also see the linked threads and discussion at Rob Braun’s, which described the original ROM disk driver and related ROM hacks.



ROM SIMM programmer utility software: Windows, Old Windows version, Mac OSX
Newer utility software maintained by dougg3:
ROM disk driver source code: romdrv1.2.sit
FC8 compression command-line tool: Windows, Mac OSX

BMOW ROM SIMM Programmer 3D-printable case: simm programmer case

ROM-inator II base ROM (512KB): baserom.rom (do not redistribute, please)

Other vendors have begun selling programmable SIMM hardware too. Friendly competition is great, but please don’t redistribute or reuse BMOW’s ROM-inator II base ROM image without permission. It’s free for personal use with your own ROM SIMM purchased from any vendor. If you’re a vendor who’s interested in selling SIMM hardware pre-programmed with the BMOW base ROM, please contact me for licensing.)

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