View source for IBM M44/44X

{{History of IBM mainframe operating systems}}
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 a modified [[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 J. Denning|Peter Denning]] as an outstanding example of experimental computer science.<ref>Denning, ''op. cit.''</ref>

The term ''[[virtual machine]]'' probably originated with the M44/44X project, from which it was later appropriated by the [[IBM CP-40|CP-40]] team to replace their earlier term ''pseudo machine''.

Unlike [[IBM CP-40|CP-40]] and later [[CP/CMS]] control programs, M44/44X did ''not'' implement a complete simulation of the underlying hardware (i.e. [[full virtualization]]). [[IBM CP-40|CP-40]] project leader [[Robert Creasy]] observed:

<blockquote>The M44/44X "was about as much of a virtual machine system as [[Compatible Time-Sharing System|CTSS]] &ndash; 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."<ref>Creasy, ''op. cit.'' &ndash; relationship between M44/44X and [[IBM CP-40|CP-40]]</ref></blockquote>

M44/44X "implanted the idea that the virtual machine concept is not necessarily less efficient than more conventional approaches" &ndash; a core assumption in the [[CP/CMS]] architecture, and one that ultimately proved very successful.<ref>L. Talkington, "A Good Idea and Still Growing", ''White Plains Development Center Newsletter'', Vol. 2, No. 3 (March 1969) [quoted in Varian, ''op. cit., p.'' 10, Note 26]</ref>

==References==
* R. J. Creasy, "[http://pages.cs.wisc.edu/~stjones/proj/vm_reading/ibmrd2505M.pdf The origin of the VM/370 time-sharing system]", ''IBM Journal of Research & Development'', Vol. 25, No. 5 (September 1981), ''pp.'' 483-490,<br/>&ndash; perspective on [[CP/CMS]] and [[VM (operating system)|VM]] history by the [[IBM CP-40|CP-40]] project lead, also a CTSS author
* Peter J. Denning, "[https://web.archive.org/web/20110928183605/http://cs.gmu.edu/cne/pjd/PUBS/ecs.pdf Performance Modeling: Experimental Computer Science at its Best]", ''[[Communications of the ACM]]'', President's Letter (November 1981)<br/> &ndash; an influential survey paper, citing the following M44/44X papers:

:* [[Laszlo Belady|L. Belady]], "A study of replacement algorithms for virtual storage computers," ''IBM Systems Journal'' Vol. 5, No. 2 (1966), ''pp.'' 78-101

:* L. Belady and C. J. Kuehner, "Dynamic space sharing in computer systems," ''Communications of ACM'' Vol. 12 No. 5 (May 1969), ''pp.'' 282-288

:* L. Belady, R. A. Nelson, and G. S. Shedler, "An anomaly in the space-time characteristics of certain programs running in paging machines," ''Communications of the ACM'' Vol. 12, No. 6 (June 1969), ''pp.'' 349-353

* {{cite conference|author=R. W. O'Neill|title=Experience using a time sharing multiprogramming system with dynamic address relocation hardware|conference=Proc. AFIPS Computer Conference 30 (Spring Joint Computer Conference, 1967)|pages=611–621|doi=10.1145/1465482.1465581}}<br/>&ndash; describes the M44/44X, reports performance measurements related to memory and paging, and discusses performance impact of multiprogramming and time-sharing
* R. A. Nelson, "Mapping Devices and the M44 Data Processing System," ''Research Report RC 1303'', IBM [[Thomas J. Watson Research Center]] (1964)<br/>&ndash; about the M44/44X
* D. Sayre, ''On Virtual Systems,'' IBM Thomas J. Watson Research Center (April 15, 1966)<br/>&ndash; an early virtual machine paper describing multiprogramming with the M44/44X.
* Melinda Varian, ''[http://www.leeandmelindavarian.com/Melinda/25paper.pdf VM and the VM community, past present, and future],'' SHARE 89 Sessions 9059-9061, 1997<br/>&ndash; the outstanding source for CP/CMS and VM history

'''Citations'''
{{Reflist}}

{{FamilyTree CP/CMS}}
{{IBM operating systems}}

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[[Category:IBM transistorized computers|M44 44X]]
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[[Category:VM (operating system)]]