Super OS/9 MMU


In the 1980’s, after Commodore introduced the University of Waterloo-influenced SuperPET, the Toronto PET User’s Group (TPUG) decided to see if the machine could be extended to support Microware Corporation’s OS/9 real time operating system.  Heavily used in the embedded space, OS/9 ran on the Motorola 6809, which was included in the SuperPET.  TPUG member Avygdor Moise designed a suitable internal PCB for the SuperPET’s M6809 socket, which TPUG manufactured.  Upon porting OS/9 to this new hardware variant, TPUG successfully launched OS/9 on the SuperPET.

Fast forward many decades.

In late 2008, a TPUG member asked if it might be possible to reverse engineer the Super OS/9 MMU board TPUG had once sold.  As the PCB was relatively simplistic, reverse engineering took little time, and multiple versions of the PCB were created.  One was a direct copy, while a final version minimized PCB real estate and simplified construction.  At that point, the project, assumed to be a fund raiser for TPUG, seemed to stall. Along the same time, SuperPET enthusiast Mike Naberezny became independently interested in ensuring this piece of history was preserved.  After obtaining scans of the original PCB, Mike reverse engineered the design, created a handmade replica, and successfully booted OS/9 on his SuperPET.  Upon sharing news of his success, Mike compared his reverse engineered design with the ones created from the TPUG materials and found they matched.  Funded by Mike, RETRO Innovations manufactured a few initial commercial PCBs based on the artwork.

Fast forward a few years.

Though the hardware was operational, the project could not yet be distributed.  Though RETRO Innovations created the specific PCB design, both it and Mike’s original handmade PCB were reverse engineered from a PCB design copyrighted by TPUG and Avy Moise.  As well, The OS/9 operating system, owned by Radisys Corporation, was not freely available for distribution.  However, through patience and continued diligence, Mike convinced all parties to allow free distribution of the hardware and software for this project in 2013

While the kits are available through RETRO Innovations, nearly all of the credit for this project’s success must go to Mike Naberezny.  Mike worked for 5 years (off and on) to reverse engineer the design, build and test, email the owning parties, and created a site detailing the history and operation of this unit.  RETRO Innovations is glad to help ensure this piece of history is available once again for use.


The Super OS/9 MMU Kit can be installed in either a 2 or 3 board SuperPET (SP9000) machine.


Super OS/9 MMU kits can be purchased in the RETRO Innovations Online Store.

Technical Details

Mike Naberezny’s Super OS/9 MMU site contains more detailed information, but essentially, this PCB extends the SuperPET expansion RAM bank selection register to offer an all-RAM (64kB) memory map.  It also provides a elegant way for the 6809 to get out of this mode.


Due to the expected low demand for this functionality and to encourage hardware assembly skills, the Super OS/9 MMU product is available only as a kit.  RETRO Innovations thanks Steven Hirsch for provided detailed construction steps for the product.  Please visit the main Super OS/9 MMU page for disk downloads and details of operation.

RETRO Innovations requests that buyers not contact Radisys or TPUG for support, as neither organization can provide such support.