“The UNIX Time-Sharing System,” by Dennis Ritchie and Ken Thompson, appeared in Communications of the ACM in July 1974. It was the first widely read account of Unix, and it introduced the system to a large audience of computer scientists outside Bell Labs. The paper was a revised version of a talk the authors had given at the Fourth ACM Symposium on Operating Systems Principles in 1973.
The paper describes Unix as a general-purpose, multi-user, interactive operating system running on the DEC PDP-11/40 and PDP-11/45. It lays out the features that defined the system: a hierarchical file system with mountable volumes, a uniform treatment of files, devices, and inter-process communication, the ability to start asynchronous processes, and a per-user command language, the shell.
A notable claim in the paper is its scope relative to its size. The authors report that the system already offered more than 100 subsystems, including over a dozen programming languages, while the resident supervisor was small. They emphasize that the system was not built on novel hardware or a grand design, but grew from the authors’ wish for a convenient computing environment.
The paper is one of the most cited and most influential documents in operating systems. By presenting Unix clearly and concisely, it spread the system’s ideas, the file model, the process model, and the small-tools approach, far beyond the lab where they were invented.