Fernando Corbato

Fernando J. Corbató is a pioneer in the development of computer operating systems. At MIT's Computation Center and Project MAC, from 1960 to 1965, he spearheaded the development of CTSS (The Compatible Time-Sharing System), which was the earliest general-purpose, time-share operating system organized for utility-like use. The CTSS file system was the first to permit controlled sharing of files among users. Variants of the multilevel processor-scheduling algorithm devised by Corbató for CTSS are used in most of today's time-sharing systems.

Corbató also led the development of Multics (Multiplexed Information and Computer Service), a joint effort of Project MAC, Bell Telephone Laboratories, and General Electric, from 1964 to 1969. Honeywell, which took over General Electric's role, later introduced Multics as a product, which still runs today. This system introduced many important concepts and techniques, including the hierarchical file system, Access Control Lists, Symbolic Naming, and Dynamic Linking, a close relationship between files and virtual memory, process structure and scheduling, and hardware-supported, ring-structured protection domains. The architectural concepts of Multics had a strong influence on many later systems, including the dynamic address translation and virtual systems capabilities of the IBM 370. The software organization of Multics likewise influenced the design of subsequent operating systems, most notably UNIX. The clock-based page-removal algorithm developed by Corbató for Multics is used in essentially all paged virtual memory systems today; the security features of Multics are still unexcelled.

CTSS and Multics stand out not only as operating systems per se but as important early examples of large-scale software engineering. Multics was written almost entirely in a high-level language (PL/I); many software engineering techniques, such as information hiding through enforced abstractions, were pioneered during the development of Multics. These systems were the work of many people and served many people. Fernando Corbató coordinated the effort, provided a clear vision of an integrated shared computing utility, and made many technical contributions of lasting importance.