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Because UNIX is a commercial product, it must be bought for each platform it runs on.
Licensing fees for UNIX versions for PC machines range from a few hundred dollars to
several thousand. In an attempt to make UNIX widely available for no cost to those who
want to experiment with it, a number of public domain UNIX systems have been developed
over the years.
One of the early UNIX workalikes was Minix, written by Andy Tanenbaum. Although
Minix didn't have a full range of features, it provided a small operating system that could be
used on PC machines. To expand on Minix, a number of users started developing an
enhanced operating system that would take advantage of the 80386 CPU's architecture. One
of the primary developers of this system, which became known as Linux, was Linus
Torvalds of the University of Helsinki. He released an early version of Linux in 1991. A
first commercial, almost bug-free release was unleashed to the programming community in
March 1992.
Soon, many programmers were working on Linux, and as the challenge and excitement of
producing a growing UNIX workalike caught on, Linux grew at a remarkable rate. As the
number of developers working on Linux grew, the entire UNIX workalike operating system
was eventually completed and now includes all the tools you will find in a commercial
UNIX product. Linux continues to grow as programmers adapt features and programs that
were originally written as commercial UNIX products to Linux. New versions of Linux and
its utilities are appearing at an astounding rate. New releases often appear weekly.
To avoid any charges for Linux, the Linux developers do not use any code from other
UNIX systems. There are no licensing fees involved with the Linux operating system, and
part of its mandate is to be freely available. Some companies have undertaken the task of
assembling and testing versions of Linux, which they package on a CD-ROM for a
(usually) minimal price.
Linux is not based on a single version of UNIX; it is a consolidation of the best features of
BSD UNIX and System V. BSD UNIX was developed at the University of California at
Berkeley, starting in 1977. Several major releases increased the power of BSD UNIX.
Several standard UNIX programs originated at BSD, although BSD stopped its UNIX
development in the early 1990s. AT&T, which developed the first version of UNIX,
continued their UNIX development by producing a series of UNIX versions called System
III, System IV, and System V. Linux uses the last primary release of BSD UNIX called
4.4BSD as its base and takes some other features from the latest release of System V, called
System V Release 4 (SVR4).
Copyrights
Just because Linux is distributed for free, it doesn't mean the software is not copyrighted.
Linux has been registered as copyrighted under the GNU General Public License (GPL),
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