The Making of the MCM/70 - Inventing the PC - page 51

André Arpin explaining the MCM /70's virtual memory at York
University in 2003. (Source: York University Computer Museum,
photograph by Z. Stachniak.)
tape, seemed like insanity, but it was actually not that bad, it
actually worked. People used that for doing some pretty serious
programming and quite successfully.”
The MCM /70's virtual memory operated under the AVS soft-
ware (A Virtual System) written by Arpin. The user had the
option of operating the MCM /70 in either the virtual or non-
virtual mode. When AVS was activated (virtual mode), both
the computer's RAM and the unused space on the cassette tape
became the user's workspace. With virtual memory imple-
mented, the MCM /70 offered in excess of 100K of memory,
an astonishing amount for such a small system. Commenting
on the virtual memory solution for the MCM /70, Arpin noted
that “if you were willing to live with the [low] speed of the ma-
chine, you could do some incredible things.” He recalled that an
MCM /70 was used to run simulations for the Pickering nuclear
plant on the north shore of Lake Ontario.