The Multics System: An Examination of Its Structure

This volume provides an overview of the Multics system developed at M.I.T.-a time-shared, general purpose utility-like system with third generation software. The advantage that this new system has over its predecessors lies in its expanded capacity to manipulate and file information on several levels and to police and control access to data in its various files. On the invitation of M.I.T.'s Project MAC, Elliott Organick developed over a period of years an explanation of the workings, concepts, and mechanisms of the Multics system. This book is a result of that effort, and is approved by the Computer Systems Research Group of Project MAC. In keeping with his reputation as a writer able to explain technical ideas in the computer field clearly and precisely, the author develops an exceptionally lucid description of the Multics system, particularly in the area of "how it works." His stated purpose is to serve the expected needs of designers, and to help them "to gain confidence that they are really able to exploit the system fully, as they design increasingly larger programs and subsystems." The chapter sequence was planned to build an understanding of increasingly larger entities. From segments and the addressing of segments, the discussion extends to ways in which procedure segments may link dynamically to one another and to data segments. Subsequent chapters are devoted to how Multics provides for the solution of problems, the file system organization and services, and the segment management functions of the Multics file system and how the user may employ these facilities to advantage. Ultimately, the author builds a picture of the life of a process in coexistence with other processes, and suggests ways to model or construct subsystems that are far more complex than could be implemented using predecessor computer facilities. This volume is intended for the moderately well-informed computer user accustomed to predecessor systems and familiar with some of the Multics overview literature. While not intended as a definitive work on this living, ever-changing system, the book nevertheless reflects Multics as it has been first implemented, and should reveal its flavor, structure and power for some time to come.