Section 1.1. History of UNIX

1.1. History of UNIX

We mentioned that Linux is a type of UNIX. Although Linux did not develop directly from an existing UNIX, the fact that it implements common UNIX standards makes the history of UNIX relevant to our discussion.

MULTiplexed Information and Computing Service (MULTICS), which is considered the precursor of the UNIX operating systems, came about from a joint venture between MIT, Bell Laboratories, and the General Electric Company (GEC), which was involved in the computer-manufacturing business at that time. The development of MULTICS was born of the desire to introduce a machine to support numerous timesharing users. At the time of this joint venture in 1965, operating systems, although capable of multiprogramming (timesharing between jobs), were batch systems that supported only a single user. The response time between a user submitting a job and getting back the output was in the order of hours. The goal behind MULTICS was to create an operating system that allowed multiuser timesharing that provided each user access to his own terminal. Although Bell Labs and General Electric eventually abandoned the project, MULTICS eventually ran in production settings in numerous places.

UNIX development began with the porting of a stripped-down version of MULTICS in an effort to develop an operating system to run in the PDP-7 minicomputer that would support a new filesystem. The new filesystem was the first version of the UNIX filesystem. This operating system, developed by Ken Thompson, supported two users and had a command interpreter and programs that allowed file manipulation for the new filesystem. In 1970, UNIX was ported to the PDP-11 and updated to support more users. This was technically the first edition of UNIX.

In 1973, for the release of the fourth edition of UNIX, Ken Thompson and Dennis Ritchie rewrote UNIX in C (a language then recently developed by Ritchie). This moved the operating system away from pure assembly and opened the doors to the portability of the operating system. Take a moment to consider the pivotal nature of this decision. Until then, operating systems were entirely entrenched with the system's architecture specifications because assembly language is extremely particular and not easily ported to other architectures. The rewrite of UNIX in C was the first step toward a more portable (and readable) operating system, a step that contributed to UNIX's sudden rise in popularity.

1974 marked the beginning of a boost in popularity of UNIX among universities. Academics began to collaborate with the UNIX systems group at Bell Laboratories to produce the fifth edition with many new innovations. This version was available free of cost and with source code to universities for educational purposes. In 1979, after many innovations, code cleanups, and an effort to improve portability, the seventh edition (V7) of the UNIX operating system came about. This version contained a C compiler and a command interpreter known as the Bourne shell.

The 1980s brought the advent of the personal computer. The workstation was now within the reach of businesses and universities. A number of UNIX variants were then developed from the seventh edition. These include Berkley UNIX (BSD), which was developed at the University of California at Berkley, and the AT&T UNIX System III and System V. Each version was then developed into other systems, such as NetBSD and OpenBSD (variants of BSD), and AIX (IBM's variant of System V). In fact, all commercial variants of UNIX are derived from System V or BSD.

Linux was introduced in 1991 at a time when UNIX was extremely popular but not available for the PC. The cost of UNIX was prohibitive and not really available to a user unless he was affiliated with a university. Linux was first implemented as an extension of an operating system called Minix (a small operating system written by Andrew Tanenbaum for educational purposes).

In the following years, the Linux kernel, combined with system software provided by the Free Software Foundation's (FSF) GNU project, made Linux^[1] develop into a sufficiently solid system that attracted attention beyond the scope of the contributing hackers. In 1994, version 1.0 of Linux was released. From then on, Linux has grown vastly, generating a demand for the distribution of Linux in mass quantities and to an increasing number of universities, corporations, and individual users that require support on various architectures.

^[1] Linux is also referred to as GNU/Linux in order to credit the component of system software provided by the FSF's GNU project.