The Making of the MCM/70 - Inventing the PC - page 53

MCM /70's operating system provided the user with a conven-
ient way to store, retrieve, and delete data and user-defined
functions from the computer's cassette. Not even as capable as
the first versions of Microsoft Windows, the MCM /70's oper-
ating system nevertheless had certain novel features that did
not appear in other operating systems for PC s until the late
1980s. One such feature was the computer's ability to be turned
off with an operating system command rather than with a
physical switch. Glenn Seeds commented on this feature of the
MCM /70's operating system: “The one thing that seemed ob-
vious to us that no one else thought of … was not having an off
switch, but powering down with an OS [operating system] com-
mand, to ensure protection of your data … Even today, the use
of automatic UPS -supported shutdown, with resume on restart,
is uncommon.” 10 Indeed, an on/off switch was nowhere to be
found on the production model of MCM 's computer. To start it,
the user had only to press the START key and the computer re-
sponded with “ MCM / APL ” on the screen to indicate that it was
ready for use. To switch the computer off, one typed “ OFF ”
and pressed the RETURN key. Before the computer could be
deactivated, the entire contents of the workspace and its status
were preserved on the cassette.

This is to ensure that nothing is accidentally destroyed. In
order to have the system restore them [the workspace and
its status] back in the computer at some later date, the cas-
sette must be mounted in the tape drive before the START
key is pressed. If this is done, the computer will automatic-
ally reconstruct the saved items in memory to appear as
though the

OFF function had never been executed. 11

The APL / EASY / AVS software on the MCM /70 made the
MCM /70 a micro-mainframe. In 1972, APL was installed ex-
clusively on mainframe computers. Virtual memory was avail-
able only on mainframe computers such as the IBM System\370