What Is UNIX
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One of the more convoluted concepts in IT is "what is UNIX" and, even more confusingly, "where does Linux fit into the UNIX world?"
UNIX began as a research operating system at AT&T in the late 1960s. For the first several years, UNIX was a "product" mostly purchased by universities. Over the next decade UNIX evolved from being a product, to becoming a family of products connected by a singular system interface standard and design philosophy.
This heritage leads to much complication and disagreement. Today there area number of UNIX family members that share some small amount of common heritage from the early days of the code base and others that have no shared code heritage. UNIX was originally its own product, then a family of products based on the code of that original product, then a certification and then a philosophy.
Linux is, far and away, the most well known and popular member of the UNIX family. Because of this, it is also one of the most heavily disputed as many people want to say that it is not a "true UNIX" because it is a clone and not derived from the original UNIX code. The creators of the original UNIX system, however, have directly stated that not only is Linux fully UNIX, it is the most pure example of it (e.g. it is the reference standard.)
Popular UNIX systems that have paid to be certified as UNIX include IBM's AIX, HP's HP-UX and Apple's Mac OSX. Popular UNIX systems that have not paid for this certification include the Linux, Solaris, OpenSolaris and BSD families.
The fragmentation and open implementations of UNIX have led not only to UNIX being a family, but truly to it being a family of families. Some, like AIX, have no derivative works and stand as a singular product. But others, like Linux, are only families and have no stock implementation (Linux exists only as family members, there is no original Linux product from which others are derived.) So the total number of UNIX systems in existence is enormous and they are extremely varied.
Since the early 1990s, the computing world has slowly eliminated all major operating system families except for Windows NT (which even itself has a small amount of UNIX heritage and came from a company that was making UNIX systems years before moving into Windows NT with Microsoft Xenix) and UNIX. UNIX has long been the dominant server operating system with dominance almost continuous increasing since around 1980 and was the basis for the design and implementation of the Internet; and in the last decade has become the dominant player in consumer equipment as well with a huge presence even in the desktop and laptop space and almost completely ownership of appliances, set top boxes, mobile devices, tablets, embedded systems and the like. UNIX is found everywhere and even at fifty years old is continuing to increase in popularity still.
What UNIX is Not: It is common for people to associate UNIX with common abstractions that often exist on it. Things like the SSH protocol, the Bourne shell family, command lines and such are in no way native or intrinsic to UNIX. Common, of course, but they themselves are not part of UNIX. UNIX shares a common interface at the C language system call layer exclusively.
