UNIX

In the late 1960s, Bell Labs was taking part, together with MIT and General Electric, in the Multics project, an ambitious time-sharing operating system. Judging the project too heavy, AT&T withdrew in 1969. Frustrated but stimulated by the experience, Ken Thompson and Dennis Ritchie, joined by Brian Kernighan, Douglas McIlroy and Rudd Canaday, decided to design a more modest system on an unused DEC PDP-7 minicomputer. Thompson wrote the first building blocks in a few weeks, and the system jokingly received the name "UNICS", soon spelled UNIX. The project was supported within Bell Labs as an internal tool for document processing and research. UNIX introduced a philosophy and an architecture that would endure. The system rested on a compact kernel, a hierarchical file system, lightweight processes communicating via input/output streams and, above all, the notion of the pipe — introduced in 1973 by McIlroy — which allowed small specialised programs to be chained into complex commands. In 1973 Dennis Ritchie rewrote most of the system in the C language, which he had designed between 1972 and 1973 from Thompson's B language; this portability was groundbreaking, since it allowed UNIX to be recompiled on other architectures. Ritchie and Thompson's founding paper, "The UNIX Time-Sharing System", appeared in the Communications of the ACM in July 1974. Distributed at low cost to universities — AT&T being unable to commercialise it before its 1984 divestiture — UNIX became the common matrix of all serious computing: Berkeley produced BSD from 1977, Sun, HP and IBM derived their commercial variants, and in 1991 Linus Torvalds took inspiration from it to create Linux. macOS, iOS, Android and the vast majority of today's servers descend directly or indirectly from UNIX. Fifty years after its creation, its concepts — file tree, shell, pipes, modular tools — still structure the entire practice of contemporary computing.