I have developed programmable ROM SIMMs for older Macintosh computers along with a programmer for flashing a ROM image to the SIMMs. Everything from the hardware design to the firmware is completely open source. The combination is pretty nifty and enables people to do all kinds of crazy things that previously weren’t possible, such as Rob Braun’s bootable ROM disk driver or changing the startup chime.

There are both 2 MB and 8 MB programmable SIMMs available. The 2 MB version has four socketed PLCC chips which can be individually programmed with a flash chip burner, or you can use my custom designed SIMM programmer to easily program all four chips directly without needing to pull them out of their sockets. The 8 MB version uses fine-pitch chips soldered directly to the SIMM, so you have to use the SIMM programmer to program them. Both the 2 MB and 8 MB SIMMs use flash memory that can be reprogrammed 100,000 times or more.

The programmer has a slot for a SIMM and connects to your computer through a USB port. It is compatible with Windows XP and higher or Mac OS X 10.5 or higher. You can also make it work in Linux if you feel like compiling the software for yourself. The software is available for download on GitHub.

The 2 MB SIMM has a pair of red LEDs (light-emitting diodes) on the back so it lights up the inside of your case. The 8 MB SIMM does not have these lights.

Since the project is open source you are free to build your own for non-commercial use, but please don’t sell the programmer commercially without my permission. If you’re interested in buying pre-assembled SIMMs and/or programmers, you can buy them from a source linked below.

These SIMMs should be compatible with the following computers:

  • Macintosh SE/30
  • Macintosh IIx
  • Macintosh IIcx
  • Macintosh IIci
  • Macintosh IIfx
  • Macintosh IIsi

It may be compatible with other models, but these are the main ones that are known to come with a SIMM socket and are known to be able to use the full 8 MB address space.


Due to personal reasons, I have been unable to continue manufacturing these ROM SIMMs and programmers. Fortunately, several people have stepped up. Steve Chamberlin sells the Mac ROM-inator II SIMM and CayMac Vintage sells SIMMs and programmers.