VM/CMS

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, of which VM is by far the most interesting. Developed starting in 1964, VM is named for its ability to run software in virtual machines which are isolated from each other; each user has the illusion of using a complete computer and can use their own operating system on this "private" computer.

CMS is a simple single-user operating system designed to run under VM. Each VM/CMS user is given their own virtual machine to run CMS in. CMS originally stood for Cambridge Monitor System, after the IBM laboratory (Cambridge, Massachusetts) where VM/CMS was developed; it was latter renamed by IBM to Conversational Monitor System.

Other operating systems that can be run in virtual machines include DOS, MVS, VM itself, Unix, MUSIC[?] and Linux. The version of Linux used is called Linux/390 and has been largely developed by IBM. Running many hundred copies of Linux simultaneously on different virtual machines has the advantage that system crashes only affect a single virtual machine and can be easily recovered from while the overall system keeps running.

While CMS originated in the days of paper terminals, by the late 1970's most users were connecting with IBM 3270 full-screen terminals.

VM 370 Welcome screen :

VM/370 ONLINE

 
                         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

 
                                                            RUNNING

Several of the development tools on CMS have been ported to other environments. The most common are the XEDIT[?] editor and the Rexx programming language.

External links:

• Bob DuCharm: Operating Systems Handbook, Part 5, http://www.snee.com/bob/opsys