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.

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"The CACM article had a dramatic impact," IT historian Peter Salus wrote in his book The Daemon, the Gnu and the Penguin. "Soon, Ken was awash in requests for Unix."

Hackers' heaven

Thompson and Ritchie were the consummate "hackers," when that word referred to someone who combined uncommon creativity, brute force intelligence and midnight oil to solve software problems that others barely knew existed.

Their approach, and the code they wrote, greatly appealed to programmers at universities, and later at startup companies without the mega-budgets of an IBM, Hewlett-Packard or Microsoft. Unix was all that other hackers, such as Bill Joy at the University of California, Rick Rashid at Carnegie Mellon University and David Korn later at Bell Labs, could wish for.

"Nearly from the start, the system was able to, and did, maintain itself," wrote Thompson and Ritchie in the CACM article. "Since all source programs were always available and easily modified online, we were willing to revise and rewrite the system and its software when new ideas were invented, discovered, or suggested by others."

Korn, an AT&T Fellow today, worked as a programmer at Bell Labs in the 1970s. "One of the hallmarks of Unix was that tools could be written, and better tools could replace them," he recalls. "It wasn't some monolith where you had to buy into everything; you could actually develop better versions." He developed the influential Korn shell, essentially a programming language to direct Unix operations, now available as open-source software.

Author and technology historian Salus recalls his work with the programming language APL on an IBM System/360 mainframe as a professor at the University of Toronto in the 1970s. It was not going well. But the day after Christmas in 1978, a friend at Columbia University gave him a demonstration of Unix running on a minicomputer. "I said, 'Oh my God,' and I was an absolute convert," says Salus.

He says the key advantage of Unix for him was its "pipe" feature, introduced in 1973, which made it easy to pass the output of one program to another. The pipeline concept, invented by Bell Labs' McIlroy, was subsequently copied by many operating systems, including all the Unix variants, Linux, DOS and Windows.

Bell Labs, Murray Hill, NJ
Unix was developed at Bell Labs' headquarters in Murray Hill, NJ. Credit: Alcatel-Lucent/Bell Labs

Another advantage of Unix -- the second "wow," as Salus puts it -- was that it didn't require a million-dollar mainframe to run on. It was written for the tiny and primitive DEC PDP-7 minicomputer because that's all Thompson and Ritchie could get their hands on in 1969. "The PDP-7 was almost incapable of anything," Salus recalls. "I was hooked."

A lot of others got hooked as well. University researchers adopted Unix in droves because it was relatively simple and easily modified, it was undemanding in its resource requirements, and the source code was essentially free. Startups like Sun Microsystems and a host of now-defunct companies that specialized in scientific computing, such as Multiflow Computer, made it their operating system of choice for the same reasons.

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