Part 1 of Essay
? The first efforts at developing a multi-user, multi-tasking operating system were begun in the 1960's in a development project called MULTICS. While working for Bell Telephone Laboratories in 1969 and 1970, Ken Thompson and Dennis Ritchie began to develop their own single-user, multi-tasking small operating system and th ....

Part 2 of Essay
.... in the 1970's, though they did share this operating system with many universities - most notably UC-Berkeley. This led to some of the variations in UNIX which we see today. After the divestiture of the Bell System, their parent company, AT&T, became much more interested in marketing a commercial version of UNIX. And today we see that many companies have now licensed their own version: AT&T's System V, Versions of System V such as SCO's Xenix and IBM's AIX Berkeley's UNIX (called "BSD" for "Berkel ....