Created originally to be a programmer friendly workbench, the uptake and influence of the UNIX operating system is a true success story.
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Philosophy
Unix was designed around a number of key concepts, which were summarized by Brian Kernighan and Rob Pike in ‘The Unix Programming Environment Publication.
These concepts helped to define key Unix features, such as multi-platform portability, multi-user and multi-tasking support, flexible hierarchical file storage, strong inter-process and network communication, plus a large collection of multipurpose scripting tools.
Early Days
Development started in the mid-1960s at the Massachusetts Institute of Technology (MIT), AT&T Bell Labs and General Electric, influenced by the earlier Multics (Multiplexed Information and Computer Services) system.
Apart from the tiny core, the system was entirely written in C. This greatly improved the portability compared to rivals, which had large chunks of machine specific assembly language.
Briefly called ‘Unics’ it was renamed to Unix in time for the first commercial release at the New York Telephone Company in 1972.
Going Commercial
During the 1970s, many academic institutions created Unix-based operating systems. Some like BSD (from the university of California, Berkeley), had a commercial friendly license agreement.
By the end of the decade, many technology companies had put Unix at the centre of their business plans. The result was a rash of Unix Systems from sequent, Hewlett Packard (HP UX) Sun (Solaris), IBM (AIX) and Microsoft (Henix) and others, all trying to outdo one another.
However, the consequence of this competition was a divergence away from the original Unix baseline. This in turn meant applications needed to be rewritten to run on each version of UNIX.
In 1988, the Institute of Electrical and Electronics Engineers (IEEE) attempted to fix this undesirable situation by publishing a common standard. Now known as POSIX, it documented a baseline structure for all the major competing Unix variants.
Yet competition between Unix distributors remained fierce. And unfortunately for end users, it would take another decade before standardization pressure resulted in meaningful application compatibility.

To be free

Richard Stallman was one of the original MIT hacker community and evangelical about free software. Unsurprisingly, he was particularly upset by the rapid commercialization of Unix. While colleagues left MIT to work on well-paid commercial projects he decided to fight back using software.
In 1938, Stallman started the GNU Project (GNU meaning GNU is Not Unix) with the aim of creating a Unix compatible system using only license-free software components. Central to this effort was the GNU General Public License (GNU GPL). However, it was a massive undertaking for one man, and Stallman only distributed the basis of a working system many years later.
Meanwhile other software hackers were attracted to a Unix-like operating system called MINIX, written for educational purposes by Andre Tanenbaum. One particularly interested party was Finnish software programmer Linus Torvalds. Taking MINIX as his starting point, he developed a free to all operating system. In 1991, he unveiled Linux, the result of all his hard work and now regarded by many as the World’s most important open source operating system.
Everywhere
Today Unix-like operating systems are everywhere: in web servers in desktop PCs, in mobile phones and tablets, in road vehicles, in aircraft and in any number of industrial, environmental and household machines.