Since the divestiture of AT&T, UNIX has become the focus of a massive marketing effort. To succeed, this effort must convince potential customers that the product is supported, that future versions will continue to be developed, and that these versions will be upwardly compatible with all past applications.

AT&T's size alone ensures that it will be around in years to come. Because the company has allocated increasing research, development, and support resources to UNIX over the past 10 years it provides an assurance of its commitment. Its massive advertising campaign for System V, its presence on the /usr/group UNIX standards committee, and the publication of the System V Interface Definition testify to the company's intention to remain compatible with past systems.

Although repeal of the law of entropy is a necessary step along the road to a viable commercial product, this runs counter to orderly system evolution. Be that as it may, AT&T's major UNIX commercialization effort has succeeded in making the system available to a much broader audience than was previously possible.

The freezing of what previously had been an ever-changing UNIX interface represented a major departure from the pattern that the small but highly skilled UNIX community had come to expect. Most early users had accounts at sites that had the source to the programs they ran. Thus, as the system interface evolved to reflect more current technology, software could be changed to keep pace. Users simply updated their programs to account for the new interface, recompiled them, and continued to use them as before. Although this required a large effort, it allowed the system -- and the tools that ran on it -- to reflect changes in software technology.

At the forefront of the technological wave was AT&T's own Bell Laboratories [Ritchie74]. It was there that the UNIX system was born and nurtured, and it was there that its evolution was controlled -- up through the release of the 7th Edition. Universities also were involved with the system almost from its inception. The University of California at Berkeley was among the first participants, playing host to several researchers on sabbatical from the Labs. This cooperation typified the harmony that was characteristic of the early UNIX community. Work that was contributed to the Labs by different members of the community helped produce a rapidly expanding set of tools and facilities.

With the release of the 7th Edition, though, the usefulness of UNIX already had been clearly established, and other organizations within AT&T began to handle the public releases of the system. These groups took far less input from the community as they began to freeze the system interface in preparation for entry into the commercial marketplace.

As the research community continued to modify the UNIX system, it found that it needed an organization that could produce releases. Berkeley quickly stepped into the role. Before the final public release of UNIX from the Labs, Berkeley's work had been focused on the development of tools designed to be added to existing UNIX systems. After the AT&T freeze, though, a group of researchers at the university found that they could easily expand their role to include the coalescing function previously provided by the Labs. Out of this came the first full Berkeley distribution of UNIX (3.0BSD), complete with virtual memory -- a first for UNIX users. The idea was so successful that System V eventually adopted it six years later. Motivations for Change

At the same time that AT&T was beginning to put the brakes on further change in UNIX, local area networks and bitmapped workstations were just beginning to emerge from Xerox PARC and other research centers. Users in the academic and research community realized that there were no production-quality operating systems capable of using such hardware. They also saw that networking unquestionably would be an indispensable facility in future systems research. Though it was not clear that UNIX was the correct base on which to build a networked system, it was clear that UNIX offered the most expedient means by which to build such a system.

This posed the Berkeley group with an interesting challenge: how to meet the needs of the community of users without adding needless complexity to existing applications. Their efforts were aided by the presence of a large and diverse local group of users who were teaching introductory programming, typesetting documents, developing software systems, and trying to build huge Lisp-based systems capable of solving differential equations. In addition, they were able to discuss current problems and hash out potential solutions at semi-annual technical conferences run by the Usenix organization.

The assistance of a steering committee composed of academics, commercial vendors, DARPA researchers, and people from the Labs made it possible for the architecture of a networking-based UNIX system to be developed. By keeping with the UNIX tradition of integrating work done by others in preference to writing everything from scratch, 4.2BSD was released less than two years later [Joy83].