1.3 Overview of the UNIX Operating System
1.3.1 Brief history of UNIX
The UNIX operating system was originally developed at AT&T Bell Labs in 1969. It was created as a tool set by programmers for programmers. The early source code was made available to universities all over the country. Programmers at the University of California at Berkeley made significant modifications to the original source code and called it BSD (Berkeley Software Distribution) UNIX. They sent this new version of the UNIX environment to other programmers around the country, who then added tools and code as they saw fit. Possibly the most important advancement made to the software by the programmers at Berkeley was the addition of networking software, which allowed the operating system to function in a local area network (LAN).

Sun's original version of UNIX, the Sun operating system (SunOS™) was based on BSD UNIX Version 4.2. At that time, AT&T's version of the UNIX environment was known as System V (system 5). In 1988, Sun OS/BSD, AT&T System 3, and XENIX were combined into what became System V Release 4 (SVR4). This new generation of the operating system was an effort to combine the best features of both BSD and AT&T UNIX and create a kind of industry standard for the operating system. This enabled software to be developed for UNIX without concern as to whether it was System V or BSD 4.2. The new SVR4 became the basis for most of the current varieties of UNIX.