TheUNIXSystem: AUNIXSystem Implementation for System/370

This paper describes an implementation of the UNIX™ operating system for IBM System/370 computers. In this implementation an underlying Resident Supervisor, adapted from an existing IBM control program, provides machine control and multiprogramming; while a UNIX System Supervisor, adapted from the standard UNIX system kernel, provides the UNIX system environment. This implementation supports multiprocessing, paging, and large-process, virtual address spaces. Terminal handling is done through an outboard terminal processor. This paper describes the software structure, with emphasis on unique aspects of this implementation: multiprocessing and process synchronization, process creation, and outboard terminal handling. Capacity and performance of the UNIX system on large mainframes is also discussed. The first and principle user of the UNIX system for System/370 is the development project for the 5ESS™ switching system. This paper also discusses the use of a large mainframe UNIX system for this development. Included in this discussion are the reasons for selecting this system for development, applications software porting, and general experience with mainframe UNIX systems.