Linux - Unix
Unix is a family of computer operating systems that derive from the original AT&T Unix originating from the AT&T Bell Labs research center in 1970s.
Different members of the family fall into following three branches:
- System V: Commercialized Unix by AT&T from 1983 onward. The last release was in 1993 and now it's available for free.
- BSD Unix: The first Berkley Software Distribution version was created by students in 1977. This is the base of FreeBSD, NetBSD and OpenBSD.
- Open Systems: Collaborative effort of multiple vendors to counter AT&T from monopolizing the market resulted in Open System v1 in 1991 but gained only minor adaptation by main AT&T competitors before dying off.
In late 1990's, Linux emerged that was the first real open and free system released under GNU license. Now Unix is more or less synonymous with Linux; not entirely accurate but close enough.