On page 8 and 9 of Appendix C, "Use of Virtual Machines in Information Systems", by John J. Donovan, May 1975, Report No,. MIT-EL-75-0100 in Information Systems to Provide Leading Indicators of Energy Sufficiency: A Report to the Federal Energy Administration, MIT-Energy Laboratory Working Paper #MIT-EL-75-004WP, June 13, 1975:

In addition to VM/370 and its predecessors, several other operational
virtual machine systems have been developed, such as the DOS/VM of PRIME
Computer, Inc. PRIME: 1974], the virtual machine capability provided under
the Michigan Terminal System (MTS) [Morrison: 1973], and a virtual machine
system for a modified PDP-11/45 used by UCLA for data security studies
[Popek & Kline: 1974].

The VMM concept, once unclerstood, is quite simple and logical. Unfortuntely,
it is sufficiently different from most conventional operating systems
that many people have difficulty in understanding the concept. The papers
[Buzen: 1973, Goldberg: 1973, Hogg: 1973, Madnick: 1969, Parmellee: 1972, and
Madnick & Donovan: 1974] give additional insight.

18. Hogg, J., and P. Madderom, "The Virtual Machine Facility — How to
Fake a 360," Internal Note , University of British Columbia and
University of Michigan Computer Center, (1973).

27. Morrison, J. E., "User Program Performance in Virtual Storage
Systems, IBM Systems Journal, vol. 12, no. 3, pp. 216-237,1973.