Unix grew up as a non-proprietary system because in 1956 AT&T had been enjoined by a federal consent decree from straying from its mission to provide telephone service. It was okay to develop software, and even to license it for a "reasonable" fee, but the company was barred from getting into the computer business.
Unix, which was developed with no encouragement from management, was first viewed at AT&T as something between a curiosity and a legal headache.
Then, in the late 1970s, AT&T realized it had something of commercial importance on its hands. Its lawyers began adopting a more favorable interpretation of the 1956 consent decree as they looked for ways to protect Unix as a trade secret. Beginning in 1979, with the release of Version 7, Unix licenses prohibited universities from using the Unix source code for study in their courses.
No problem, said computer science professor Andrew Tanenbaum, who had been using Unix V6 at Vrije Universiteit in Amsterdam. In 1987 he wrote a Unix clone for use in his classrooms, creating the open-source Minix operating system to run on the Intel 80286 microprocessor.
"Minix incorporated all the ideas of Unix, and it was a brilliant job," Salus says. "Only a major programmer, someone who deeply understood the internals of an operating system, could do that." Minix would become the starting point for Linus Torvalds' 1991 creation of Linux -- if not exactly a Unix clone, certainly a Unix look-alike.
Stepping back a decade or so, Bill Joy, who was a graduate student and programmer at the University of California at Berkeley in the '70s, got his hands on a copy of Unix from Bell Labs, and he saw it as a good platform for his own work on a Pascal compiler and text editor.
Modifications and extensions that he and others at Berkeley made resulted in the second major branch of Unix, called Berkeley Software Distribution (BSD) Unix. In March 1978, Joy sent out copies of 1BSD, priced at $50.
So by 1980 there were two major lines of Unix, one from Berkeley and one from AT&T, and the stage was set for what would become known as the Unix Wars. The good news was that software developers anywhere could get the Unix source code and tailor it to their needs and whims. The bad news was they did just that. Unix proliferated, and the variants diverged.
In 1982 Joy co-founded Sun Microsystems and offered a workstation, the Sun-1, running a version of BSD called SunOS. (Solaris would come about a decade later.) The following year, AT&T released the first version of Unix System V, an enormously influential operating system that would become the basis for IBM's AIX and Hewlett-Packard's HP-UX.
The Unix wars
In the mid-'80s, users, including the federal government, complained that while Unix was in theory a single, portable operating system, in fact it was anything but. Vendors paid lip service to the complaint but worked night and day to lock in customers with custom Unix features and APIs.
In 1987, Unix System Laboratories, a part of Bell Labs at the time, began working with Sun on a system that would unify the two major Unix branches. The product of their collaboration, called Unix System V Release 4.0, was released two years later and combined features from System V Release 3, BSD, SunOS and Microsoft's Xenix.
Other Unix vendors feared the AT&T/Sun alliance. The various parties formed competing "standards" bodies with names like X/Open, Open Software Foundation, Unix International and Corporation for Open Systems. The arguments, counter-arguments and accomplishments of these groups would fill a book, but they all claimed the high road to a unified Unix while taking potshots at each other.