UNIX was developed at Bell Labs (AT&T) in the early 1970's. Several universities bought it along with a license for the source code, and the University of California at Berkeley rewrote and enhanced much of the system from 1979 to 1994. They eventually released the BSD version of UNIX, but it was legally encumbered by the AT&T copyright that still covered parts of the source. Users of BSD had to purchase an expensive source license from AT&T.
In 1991, Berkeley's Computer Science Research Group (CSRG) removed the parts of BSD 4.3 that had been written by AT&T and released the remainder as the Berkeley Networking Release 2 (Net/2). Bill and Lynne Jolitz rewrote the missing pieces, completed Net/2's mostly-complete port to the i386, and released 386BSD 0.0. This was followed immediately by a slightly less buggy 386BSD 0.1, and an indefinitely delayed bug-free 0.2 release caused several groups to start their own BSD release. The FreeBSD group took 386BSD, added enhancements, and have been releasing BSD for the IBM PC line of machines regularly. The NetBSD group decided to release a research version of 386BSD, and they now have ports to more than half a dozen machines. The NetBSD system is best suited to handle different architectures and it is recommended that new ports be based on NetBSD's source tree. The author and four other students (Brad Grantham, Allen Briggs, Mike Finch, and Chris Caputo) ported NetBSD to the Macintosh, and that port is now released as part of the standard NetBSD distribution.