Unix turns 40: The past, present and future of a revolutionary OS

After four decades, the future of the operating system is clouded, but its legacy will endure.

Forty years ago this summer, a programmer sat down and knocked out in one month what would become one of the most important pieces of software ever created.

In August 1969, Ken Thompson, a programmer at AT&T subsidiary Bell Laboratories, saw the month-long departure of his wife and young son as an opportunity to put his ideas for a new operating system into practice. He wrote the first version of Unix in assembly language for a wimpy Digital Equipment Corp. (DEC) PDP-7 minicomputer, spending one week each on the operating system, a shell, an editor and an assembler.

Thompson and a colleague, Dennis Ritchie, had been feeling adrift since Bell Labs had withdrawn earlier in the year from a troubled project to develop a time-sharing system called Multics (Multiplexed Information and Computing Service). They had no desire to stick with any of the batch operating systems that predominated at the time, nor did they want to reinvent Multics, which they saw as grotesque and unwieldy.

After batting around some ideas for a new system, Thompson wrote the first version of Unix, which the pair would continue to develop over the next several years with the help of colleagues Doug McIlroy, Joe Ossanna and Rudd Canaday. Some of the principles of Multics were carried over into their new operating system, but the beauty of Unix then (if not now) lay in its less-is-more philosophy.

"A powerful operating system for interactive use need not be expensive either in equipment or in human effort," Ritchie and Thompson would write five years later in the Communications of the ACM (CACM), the journal of the Association for Computing Machinery. "[We hope that] users of Unix will find that the most important characteristics of the system are its simplicity, elegance, and ease of use."

Apparently they did. Unix would go on to become a cornerstone of IT, widely deployed to run servers and workstations in universities, government facilities and corporations. And its influence spread even farther than its actual deployments, as the ACM noted in 1983 when it gave Thompson and Ritchie its top prize, the A.M. Turing Award for contributions to IT: "The model of the Unix system has led a generation of software designers to new ways of thinking about programming."

Early steps

Ken Thompson and Dennis Ritchie
Thompson and Ritchie in the early days of Unix.

Of course, Unix' success didn't happen all at once. In 1971 it was ported to the PDP-11 minicomputer, a more powerful platform than the PDP-7 for which it was originally written. Text-formatting and text-editing programs were added, and it was rolled out to a few typists in the Bell Labs Patent department, its first users outside the development team.

In 1972, Ritchie wrote the high-level C programming language (based on Thompson's earlier B language); subsequently, Thompson rewrote Unix in C, which greatly increased the OS' portability across computing environments. Along the way it picked up the name Unics (Uniplexed Information and Computing Service), a play on Multics; the spelling soon morphed into Unix.

It was time to spread the word. Ritchie and Thompson's July 1974 CACM article, "The UNIX Time-Sharing System," took the IT world by storm. Until then, Unix had been confined to a handful of users at Bell Labs. But now with the Association for Computing Machinery behind it -- an editor called it "elegant" -- Unix was at a tipping point.

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