os/360

The third episode takes us into the 1960s — a time of major breakthroughs in operating systems.For the first time, hardware and software were unified, and concepts such as multitasking and multi-user access emerged.The key systems of this era were IBM’s OS/360 and the experimental MULTICS project, co-developed by MIT, Bell Labs, and General Electric — both of which defined the standards for memory management, security, and user interaction. Context – The Need for Unification and Multitasking Before the 1960s, the mainframe market was fragmented — every model had its own operating system.This led to high maintenance costs and limited capabilities in single-user, batch-only environments. In 1964, IBM launched the System/360 — a family of compatible machines, from small to large, all using a unified architecture and instruction set.This created a need for one operating system to support the entire family: OS/360. OS/360 – One OS for the Whole Hardware Range OS/360 was not a single system, but a family of operating systems tailored to different hardware tiers and user groups: Version Description Notes PCP Primary Control Program Simple single-task system for early installs MFT Multiprogramming with Fixed number of Tasks Fixed partitions, supported multitasking MVT Multiprogramming with Variable number of Tasks Dynamic memory allocation, advanced management There was also DOS/360 for smaller System/360 models — a simplified version of the OS. IBM System/360 Model 40 by U.S. Department of Agriculture, Public domain Key innovations in OS/360: OS/360 left a deep mark on the development of mainframe OSes and directly led to modern IBM systems like z/OS. MULTICS – A Vision of Secure, Shared-Time Systems At the same time, MIT, Bell Labs, and General Electric were co-developing MULTICS (Multiplexed Information and Computing Service),a pioneering OS built for multi-user, time-sharing environments. Key features of MULTICS: Though MULTICS never gained commercial success, it had a massive influence on the development of OS architecture and security models. Competition and Legacy of Multi-User Systems Despite their differences in commercial adoption, OS/360 and MULTICS were highly influential: Feature OS/360 MULTICS Launch Year 1964 1969 Processing Model Batch + multitasking Multi-user, time-sharing Memory Architecture Partitioned + dynamic allocation Virtual memory Security Basic protection (MVT) Advanced ring-based security Adoption Widely used, IBM standard Limited installations (experimental) Ideas from OS/360 evolved into MVS and OS/390; MULTICS inspired the design of UNIX. Other Notable Systems of the Era – Advancing Multitasking and Time-Sharing CTSS (Compatible Time-Sharing System) (1961–1966)Developed at MIT, it introduced interactive multi-user sessions on the IBM 7094. GE COS / GCOSGeneral Electric’s OS that competed with IBM, enabling simultaneous task execution. Burroughs MCP (Master Control Program) (1961)Possibly the first OS with a high-level language kernel (ALGOL), featuring memory protection and resource control. Conclusion The years 1964–1969 laid the groundwork for modern operating systems.IBM’s OS/360 unified its hardware ecosystem and pioneered batch multitasking with memory and device control.Meanwhile, MULTICS set new standards in time-sharing, security, and modularity — concepts that later shaped UNIX and its descendants. In the next episode, we’ll explore UNIX and BSD, tracing their roots back to the collaborative, multi-user systems of the late 1960s.