
IBM M44/44X

The IBM M44/44X was an experimental computer system from the mid-1960s, designed and operated at IBM's Thomas J. Watson Research Center at Yorktown Heights, New York. It was based on an IBM 7044 (the 'M44'), and simulated multiple 7044 virtual machines (the '44X'), using both hardware and software. Key team members were Dave Sayre and Rob Nelson. This was a groundbreaking machine, used to explore paging, the virtual machine concept, and computer performance measurement. It was purely a research system, and was cited in 1981 by Peter Denning as an outstanding example of experimental computer science.
The term "virtual machine" probably originated with the M44/44X project, from which it was later appropriated by the CP-40 team to replace their earlier term "pseudo machine".
Unlike CP-40 and later CP/CMS control programs, M44/44X did "not" implement a complete simulation of the underlying hardware (i.e. full virtualization). CP-40 project leader Robert Creasy observed:
The M44/44X "was about as much of a virtual machine system as CTSS – which is to say that it was close enough to a virtual machine system to show that 'close enough' did not count. I never heard a more eloquent argument for virtual machines than from Dave Sayre."
M44/44X "implanted the idea that the virtual machine concept is not necessarily less efficient than more conventional approaches" – a core assumption in the CP/CMS architecture, and one that ultimately proved very successful.
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