June 5, 2023

Vintage computing enthusiast Michael Gardi has been working on bringing another long-forgotten beast back from the grave — this time creating a full-size reproduction of the Micro Computer Mahcines MCM/70, a true personal computer released in Toronto in the 1970s.

“The MCM/70 computer was conceived, developed, and built in Canada in 1974,” Gardi offers by way of background to the project. “It was arguably one of the very first ‘personal’ computers because it was portable, had a built-in keyboard, display, and support for the APL programming language, plus cassette storage. On the other hand, at a cost of $10,000, it was only really accessible to large corporations, the military, governments, and educational institutions.”

Gardi’s replica, naturally, is designed to be somewhat more affordable — doubly so when taking inflation into account. Having given up hope on finding original hardware, Gardi turned to emulation — replacing the Intel 8008, 8kB of RAM, an 32kB ROM of the original device with more modern hardware running an MCM/70 emulator developed at the York University Computer Museum running on a Raspberry Pi single-board computer.

With the idea to be as authentic to the original design as possible, though, Gardi wasn’t happy with just slapping a modern monitor into the mix — and instead set about finding a replacement for the original’s Burroughs Self-Scan Model C4047 plasma display. “I spent a lot of time looking for a suitable replacement and think I found one,” Gardi writes, “the Broadcom HCMS-2972. Packaged as eight 5×7 dot matrix arrays these modules operate at a nice safe 3.3V and can be cascaded together side by side to create the 32×1 character display desired here.”

The keyboard, meanwhile, was swapped out for a modified version of a replica Ohio Scientific unit — and everything is housed in a 3D-printed replica of the original chassis, in lieu of injection molding capabilities. The replica even includes a pair of cassette tape decks, just as the original design — though Gardi’s versions accept RFID-tagged 3D-printed fake cassettes which load image files from the Raspberry Pi’s storage, allowing for a reasonably authentic software-loading experience.

The tape drives are fake, yet one is functional — recognizing pseudo-cassettes via RFID to load image files. (📹: Michael Gardi)

This is far from Gardi’s first attempt to resurrect an unusual vintage computer. Back in 2020 he created a 3D-printable version of the “Paperclip Computer” from the 1968 book How to Build a Working Digital Computer by Edward Alcosser, James P. Phillips, and Allen M. Wolk. A year earlier he had built the Digi-Comp I Redux, based on an educational device from the 1960s. The maker has even put together a functional recreation of the DEC H-500 Computer Lab, complete with guide to make your own.

“With autostart done,” Gardi concludes, referring to his configuration of the Raspberry Pi to boot directly into the emulator, “and the tape sensors integrated into the MCM/70 Emulator, this project is complete. My game plan going forward is to work my way through the MCM/70 Users Guide to test my implementation and learn the APL language.”

Gardi’s full write-up is available on Hackaday.io.