A Quick History of UNIX

In 1969, Ken Thompson, Dennis Ritchie and others started work on what was to become UNIX on a "little-used PDP-7 in a corner" at AT&T Bell Labs. For ten years, the development of UNIX proceeded at AT&T in numbered versions. V4 (1974) was re-written in C -- a major milestone for the operating system's portability among different systems. V6 (1975) was the first to become available outside Bell Labs -- it became the basis of the first version of UNIX developed at the University of California Berkeley.
Bell Labs continued work on UNIX into the 1980s, culminating in the release of System V (five) in 1983 and System V, Release 4 (abbreviated SVR4) in 1989.The Berkeley Standard Distribution (BSD) became a second major variant of "UNIX." It was widely deployed in both university and corporate computing environments starting with the release of BSD 4.2 in 1984. Some of its features were incorporated into SVR4.
As the 1990s opened, AT&T's source code licensing had created a flourishing market for hundreds of UNIX variants by different manufacturers. AT&T sold its UNIX business to Novell in 1993, and Novell sold it to the Santa Cruz Operation two years later. In the meantime, the UNIX trademark had been passed to the X/Open consortium, which eventually merged to form The Open Group.1
While the stewardship of UNIX was passing from entity to entity, several long-running development efforts started bearing fruit. Traditionally, in order to get a BSD system working, you needed a source code license from AT&T. But by the early 1990s, Berkeley hackers had done so much work on BSD that most of the original AT&T source code was long gone. A succession of programmers, starting with William and Lynne Jolitz, started work on the Net distribution of BSD, leading to the release of 386BSD version 0.1 on Bastille Day, 1992. This original "free source" BSD was spun out into three major distributions, each of which has a dedicated following: NetBSD, FreeBSD, and OpenBSD, all of which are based on BSD 4.4.2
BSD wasn't the first attempt at a "free" UNIX. In 1984, programmer Richard Stallman started work on a free UNIX clone known as GNU (GNU's Not UNIX). By the early 1990s, the GNU Project had achieved several programming milestones, including the release of the GNU C library and the Bourne Again SHell (bash). The whole system was basically finished, except for one critical element: a working kernel.

Enter Linus Torvalds, a student at the University of Helsinki in Finland. Linus looked at a small UNIX system called Minix and decided he could do better. In the fall of 1991, he released the source code for a freeware kernel called "Linux" -- a combination of his first name and Minux, pronounced lynn-nucks.3 By 1994, Linus and a far-flung team of kernel hackers were able to release version 1.0 of Linux. Linus and friends had a free kernel; Stallman and friends had the rest of a free UNIX clone system: People could then put the Linux kernel together with GNU to make a complete free system. This system is known as "Linux," though Stallman prefers the appellation "GNU/Linux system."4 There are several distinct GNU/Linux distributions: some are available with commercial support from companies like Red Hat, Caldera Systems, and S.U.S.E.; others, like Debian GNU/Linux, are more closely aligned with the original free software concept.