Where Did UNIX Come From and Why Are There Different Versions Of UNIX?

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 they chose the name UNIX. Their initial goal was simply to operate
their DEC PDP machines more effectively. In 1971, UNIX became multi-user and
multi-tasking, but it was still just being developed by a small group of
programmers who were trying to take advantage of the machines they had at hand.
(In other words, this operating system that they were developing did not run on
any machine made by Bell!)

In 1973, Dennis Ritchie rewrote the UNIX operating system in C (a language he
had developed.) And in 1975, the portability of the C programming language was
used to "port" UNIX to a wide variety of hardware platforms. For legal reasons,
Bell Labs was not able to market UNIX 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 "Berkeley System Development"),
Versions of Berkeley UNIX such as Sun Microsystem\'s SunOS, DEC\'s Ultrix and
Carnegie Mellon University\'s Mach
(used on the NEXT).

Category: Technology