It's all about the history!
1969 The Beginning The history of UNIX starts back in 1969, when Ken Thompson, Dennis Ritchie and others started working on the "little-used PDP-7 in a corner" at Bell Labs and what was to become UNIX.
1971 First Edition It had a assembler for a PDP-11/20, file system, fork(), roff and ed. It was used for text processing of patent documents.
1973 Fourth Edition It was rewritten in C. This made it portable and changed the history of OS's.
1975 Sixth Edition UNIX leaves home. Also widely known as Version 6, this is the first to be widely available out side of Bell Labs. The first BSD version (1.x) was derived from V6.
1979 Seventh Edition It was a "improvement over all preceding and following Unices" [Bourne]. It had C, UUCP and the Bourne shell. It was ported to the VAX and the kernel was more than 40 Kilobytes (K).
1980 Xenix Microsoft introduces Xenix. 32V and 4BSD introduced.
1982 System III AT&T's UNIX System Group (USG) release System III, the first public release outside Bell Laboratories. SunOS 1.0 ships. HP-UX introduced. Ultrix-11 Introduced.
1983 System V Computer Research Group (CRG), UNIX System Group (USG) and a third group merge to become UNIX System Development Lab. AT&T announces UNIX System V, the first supported release. Installed base 45,000.
1984 4.2BSD University of California at Berkeley releases 4.2BSD, includes TCP/IP, new signals and much more. X/Open formed.
1984 SVR2 System V Release 2 introduced. At this time there are 100,000 UNIX installations around the world.
1986 4.3BSD 4.3BSD released, including internet name server. SVID introduced. NFS shipped. AIX announced. Installed base 250,000.
1987 SVR3 System V Release 3 including STREAMS, TLI, RFS. At this time there are 750,000 UNIX installations around the world. IRIX introduced.
1988 POSIX.1 published. Open Software Foundation (OSF) and UNIX International (UI) formed. Ultrix 4.2 ships.
1989 AT&T UNIX Software Operation formed in preparation for spinoff of USL. Motif 1.0 ships.
1989 SVR4 UNIX System V Release 4 ships, unifying System V, BSD and Xenix. Installed base 1.2 million.
1990 XPG3 X/Open launches XPG3 Brand. OSF/1 debuts. (Plan 9 from Bell Labs ships.)
1991 UNIX System Laboratories (USL) becomes a company - majority-owned by AT&T. Linus Torvalds commences Linux development. Solaris 1.0 debuts.
1992 SVR4.2 USL releases UNIX System V Release 4.2 (Destiny). October - XPG4 Brand launched by X/Open. December 22nd Novell announces intent to acquire USL. Solaris 2.0 ships.
1993 4.4BSD 4.4BSD the final release from Berkeley. June 16 Novell acquires USL
Late 1993 SVR4.2MP
Novell transfers rights to the "UNIX" trademark and the Single UNIX Specification to X/Open. COSE initiative delivers "Spec 1170" to X/Open for fasttrack.
In December Novell ships SVR4.2MP , the final USL OEM release of System V
1994 Single UNIX Specification BSD 4.4-Lite eliminated all code claimed to infringe on USL/Novell. As the new owner of the UNIX trademark, X/Open introduces the Single UNIX Specification (formerly Spec 1170), separating the UNIX trademark from any "actual code" stream.
Plan 9 demonstrated that an integral concept of Unix—that every system interface could be represented as a set of files—could be successfully implemented in a modern distributed system. Some features from Plan 9, like the UTF-8 character encoding of Unicode, have been implemented in other operating systems, although UNSUCCESSFULLY as X11 has no Unicode support!