Programming languages and software engineering - The Computing Universe: A Journey through a Revolution - page 72

which applications are potentially impacted by the change. Such empirical
software engineering tools are enabling maintenance software engineers to
make informed, data-driven decisions about their priorities.
Open-source software
A very different model of software development is the philosophy pro-
moted by the open-source software movement. One of the origins of this move-
ment was the decision of AT&T to allow the distribution of the Unix source
code under a “free” license (see section on Unix and C). Bell Labs researchers
Ken Thompson and Dennis Ritchie wrote the Unix operating system in the
early 1970s. It was the first operating system to be written in a high-level
language, the C programming language developed by Ritchie. The source
code for the C compiler developed by Bell Labs researcher Stephen Johnson
was also freely distributed with the Unix code. For only a few-hundred-dollar
licensing fee, the university research community could obtain not only a
functional operating system but also a platform for teaching and research. In
1956, AT&T had settled an antitrust monopoly suit with the U.S. Department
of Justice, and AT&T's lawyers interpreted the agreement as forbidding the
company to enter new markets not related to telephones. The AT&T license
agreement for Unix was intended to make it crystal clear that the company
was not creating a new business with computers:
The terms of the early Unix licenses were minimal: The software came “as is”
with no royalties to AT&T, but also no support and no bug fixes.19 19
One immediate result of this license agreement was to encourage the research
community to set up self-help networks and share information on bug fixes.
This set the style for the development of a global Unix support and development
community with developers freely sharing their suggested code changes. The
most significant research collaboration focused on Unix was between the origi-
nal Bell Labs team of Richie and Thompson and the Computer Systems Research
Group (CSRG) at the University of California, Berkeley. In 1983, the CSRG team
released the latest version of their “Berkeley Unix” software, known as 4.2 BSD.
This software incorporated the new Internet protocols and allowed Unix systems
to be easily connected to the rapidly growing Internet. The initials BSD stand for
Berkeley Software Distribution, which included an open-source software license
B.4.8. Richard Stallman is the originator of the free software movement. In 1979 he was working in
the AI lab at MIT when the lab installed a new laser printer from Xerox. The printer suffered from
paper jams and Stallman wanted access to the source code of the printer driver so he could modify
it and fix the problem. Xerox would not give him the source code and he ended up being very
frustrated. In 1984 Stallman resigned from MIT to set up the Free Software Foundation. Stallman
was very explicit in his explanation of “free”: “Since free refers to freedom, not to price, there is no
contradiction between selling copies and free software.” B4 He called his project to build a free oper-
ating system by the recursive acronym GNU - standing for GNU's Not Unix. He also devised the GPL
source license that was designed to ensure that any modifications to the source code were covered
by the same license, including combinations of GPL software with commercial software.