The design and implementation of a virtual machine operating system using a Virtual Access Method

Abstract

In the autumn of 1969, we decided to try a new approach to the design of a virtual machine operating system. Until that time, most installations using Virtual Machine Monitors merely ran operating systems that already existed for “stand-alone” use. Few, if any, installations had attempted to design and create an operating system that took advantage of its running environment. The Virtual Machine Monitor we were using was a highly modified version of CP-67 which was designed to operate on an IBM S/360 Model 67. Our design motivation centered on the reduction of CP-67 overhead by reducing the amount of virtual memory required to support the operating system. A secondary design goal was to produce a “production oriented” system. The resulting operating system should be able to be “tailored” to a particular user's requirements. The design of the New System (NS), as it came to be called, revolved around the fact that it not only knew it was executing within a virtual machine, but took advantage of it. Special communication links were designed and installed allowing NS to more directly control its paging and I/O profile.