Virtually Machines

Intro to Management Information Systems

221

Virtual Machine

Charles Howard

Table of Content

* History of Virtual Machines

* What is a Virtual Machine?

* Hardware Emulation

* Software-Specific Applications

* Systems that Use Hardware And Software

* Reference

History of Virtual Machines

When IBM introduced the 360 models 67, circa 1967, it was IBM’s first major system with virtual memory. When the machine was announced a software system called TSS was promised. Perhaps this was a reaction to the earlier Multics announcement. TSS was a substantial departure from IBM’s other systems and was slow to be delivered. A team of IBM people in Cambridge MA conceived and built a program for the 67 that would provide the illusion of several standard 360’s which lacked virtual memory. This program was called CP 67. The Cambridge team also produced a simple interactive one user operating system called CMS. CMS would run happily and efficiently on one of the virtual machines provided by CP 67, or on a real 360 for that matter. Tom Van Vleck provides very interesting history and references. In fact he provides much of the information that I had intended to write here. I will repeat little of his information here.

As of several years ago, VM/370, a direct descendant of CP 67, was used about equally by users of CMS and those who needed to run various alternate operating systems for reasons such as testing.

Today a rather direct descendant of CMS runs on VM/390. IBM has had a policy for about two decades now of phasing out VM. It is yet heavily used inside and outside of IBM. Ironically the developers of competing operating system within IBM use CP/390 very heavily to test and debug their systems. IBM now (1999) recommends VM/390 for Y2K testing. Here is an interesting brochure describing IBM’s 2006 virtual offering, which claims VM/370 heritage.

VMware provides a similar system for Intel 32 bit machines. Many of the points of...