An efficient virtual machine implementation

Abstract

This paper describes the techniques used to implement an efficient virtual machine facility within MTS for the IBM System/360 Model 67. The goals of the project were to support the IBM Operating System, including the Indexed Sequential Access Method and Teleprocessing capabilities, as a subsystem under MTS with a maximum teleprocessing degradation of 30% for OS/360 programs and complete protection between OS/360 and MTS. The first attempt, using channel program relocation similar to that employed by CP-67, provided unacceptable response to teleprocessing requests which required indexed accesses to the data base. The second attempt obviated the need for most software relocation of channel programs by assuring that the OS/360 buffer areas and channel programs were allocated to main storage having addresses identical to their virtual addresses. Storage protection was accomplished by a hardware change to the IBM System/360 protection mechanism which created a two-level hierarchy of storage keys. Using these techniques the virtual machine met the goals of the project. The techniques employed are applicable to virtual memory systems other than MTS and the IBM System/360 Model 67