The UNIX Time-sharing System--A Retrospective

By Dennis M. Ritchie

UNIX is a general-purpose, interactive time-sharing operating system for the DEC PDP-11 and Interdata 8/32 computers. Since it became operational in 1971, it has become quite widely used. This paper discusses the strong and weak points of UNIX and some areas where we have expended no effort. The following areas are touched on:

• The structure of files: a uniform, randomly-addressable sequence of bytes. The irrelevance of the notion of ``record.'' The efficiency of the addressing of files.
• The structure of file system devices; directories and files.
• I/O devices integrated into the file system.
• The user interface: fundamentals of the shell, I/O redirection, and pipes.
• The environment of processes: system calls, signals, and the address space.
• Reliability: crashes, losses of files.
• Security: protection of data from corruption and inspection; protection of the system from stoppages.
• Use of a high-level language--the benefits and the costs.
• What UNIX does not do: ``real-time,'' interprocess communication, asynchronous I/O.
• Recommendations to system designers.

NOTE: * A version of this paper was presented at the Tenth Hawaii International Conference on the System Sciences, Honolulu, January, 1977.

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The Evolution of the Unix Time-sharing System

By Dennis M. Ritchie

This paper presents a brief history of the early development of the Unix operating system. It concentrates on the evolution of the file system, the process-control mechanism, and the idea of pipelined commands. Some attention is paid to social conditions during the development of the system.

NOTE: *This paper was first presented at the Language Design and Programming Methodology conference at Sydney, Australia, September 1979. The conference proceedings were published as Lecture Notes in Computer Science #79: Language Design and Programming Methodology, Springer-Verlag, 1980. This rendition is based on a reprinted version appearing in AT&T Bell Laboratories Technical Journal 63 No. 6 Part 2, October 1984, pp. 1577-93.

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The UNIX Time-Sharing System

By D. M. Ritchie and K. Thompson

Unix is a general-purpose, multi-user, interactive operating system for the larger Digital Equipment Corporation PDP-11 and the Interdata 8/32 computers. It offers a number of features seldom found even in larger operating systems, including

• A hierarchical file system incorporating demountable volumes,
• Compatible file, device, and inter-process I/O,
• The ability to initiate asynchronous processes,
• System command language selectable on a per-user basis,
• Over 100 subsystems including a dozen languages,
• High degree of portability.

This paper discusses the nature and implementation of the file system and of the user command interface.

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