Unix
The Open Group holds the definition of what a UNIX system is. In 1994, Novell got out of business. Rather than sell the business as a single entity, Novell transferred the rights to the UNIX trademark and the specification to The Open Group (at the time X/Open Company). Subsequently, it sold the source code and the product implementation (UNIXWARE) to SCO. The Open Group also owns the trademark UNIXWARE.
Today, the definition of UNIX ® takes the form of the worldwide Single UNIX Specification integrating X/Open Company’s XPG4, IEEE’s POSIX Standards and ISO C. Through continual evolution, the Single UNIX Specification is the defacto and dejure standard definition for the UNIX system application programming interfaces. As the owner of the UNIX trademark, The Open Group has separated the UNIX trademark from any actual code stream itself, thus allowing multiple implementations. Since the introduction of the Single UNIX Specification, there has been a single, open, consensus specification that defines the requirements for a conformant UNIX system.
There is also a mark, or brand, that is used to identify those products that have been certified as conforming to the Single UNIX Specification, initially UNIX 93, followed subsequently by UNIX 95, UNIX 98 and now UNIX 03.
The Open Group is committed to working with the community to further the development of standards conformant systems by evolving and maintaining the Single UNIX Specification and participation in other related standards efforts. Recent examples of this are making the standard freely available on the web, permitting reuse of the standard in open source documentation projects , providing test tools ,developing the POSIX and LSB certification programs.
From this page you can read about the history of the UNIX system over the past 40 years or more. You can learn about the Single UNIX Specification, and read or download online versions of the specification. You can also get involved in the ongoing development and maintenance of the Single UNIX Specification, by joining the Austin Group whose approach to specification development is “write once, adopt everywhere“, The Open Group’s Base Working Group or get involved in the UNIX Certification program.
You can find more details by referring the following url:
https://en.wikipedia.org/wiki/Unix
http://www.webopedia.com/TERM/U/UNIX.html
http://www.unix.org/