From Academic Kids

VM/CMS (Virtual Machine/Conversational Monitor System, originally called CP/CMS when it first appeared) is an IBM system used on System/360, System/370, System/390 and zSeries IBM mainframes.

(Other operating systems for the same hardware are the members of the MVS - OS/390 - Z/OS family.)

VM/CMS has two main components, VM and CMS, each an independent operating system. VM is a virtual machine operating system which provides each user with what seems to be their own personal mainframe; CMS is a relatively simple single-user operating system, designed to run principally under VM. Each VM/CMS user is given their own virtual machine to run CMS in. When used with CMS, VM is an operating system which can support users, and not just a hypervisor.



Development started on what was then called the "CP-40 Project", working with a modified System 360 Model 40, at IBM's Cambridge Scientific Center (CSC) in the Fall of 1964. CP-40 was a virtual machine operating system; a simple interactive computing single-user operating system, CMS, was designed to go along with it. Actual implementation started in 1965, and the complete system was first available to users in early 1966.

VM/CMS was not started as a formal IBM product, and for many years there was a great deal of political infighting within IBM, over what resources should be available to it, as compared with competing IBM products.

After IBM announced the System 360 Model 67, the software was converted to run on that; CP-40 was renamed CP-67 at that point. An early version of the system was installed at MIT's Lincoln Laboratory in 1967, because of Lincoln's dissatisfaction with the "standard" IBM time-sharing offering, TSS (Time Sharing System), which was at that time very slow and unreliable. Lincoln personnel co-operated with CSC in improving the system; another influential IBM customer, Union Carbide, also decided to run VM/CMS, and also contributed to its development.

By early 1968, word had spread, and most System 360/67 sites were actually running VM/CMS, not the "official" IBM system for the machine, TSS. This eventually led to the demise of TSS, in 1971.

Thereafter, the utility of the system (especailly within IBM, where it was heavily used in developing MVS) prevented all attempts to kill it, and IBM finally accepted the inevitable with relatively good grace, having learned through internal experience just how useful it was.

VM/CMS today

IBM and third parties offer many applications for VM/CMS. Perhaps the most famous was OfficeVision, although today third parties offer HTTP servers, databases, etc.

VM 370 Welcome screen:


                        VV        VV    MM        MM
                        VV        VV    MMM      MMM
                        VV        VV    MMMM    MMMM
                        VV        VV    MM MM  MM MM
                 3333333333     777777777777MMMM  00000000
                333333333333    77777777777  MM  0000000000
                33      VV33    77VV    77      00MM      00
                         V33     VV    77M      00MM      00
                          33    VV    77MM      00MM      00
                       3333VV  VV    77 MM      00MM      00
                       3333 VVVV     77 MM      00MM      00
                          33 VV      77 MM      00MM      00
                          33         77         00        00
                33        33         77         00        00
                333333333333         77          0000000000
                 3333333333          77           00000000


Further Reading

  • Melinda Varian, VM and the VM Community: Past, Present, and Future (available online here (http://pucc.princeton.edu/~melinda/)) is an excellent detailed history, starting with CP-40 and its roots.
  • Bob DuCharm, Operating Systems Handbook, Part 5: VM/CMS (availble online here (http://www.snee.com/bob/opsys/part5vmcms.pdf)) is a fairly detailed user's guide to VM/CMS.

See also

External links


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