[rst]

Actually, Unix was made available only under closed-source license (most notably as "Unix System V" and its commercial derivatives, including AIX and Solaris). This lead to, among other things, a nasty lawsuit against the University of California at Berkeley, who eventually did make their BSD Unix variant publicly available, after carefully excising most of the AT&T-copyrighted code.

Wikipedia has some information on the relevant history. As usual, treat with skepticism, but it will confirm the basics:

on System V: http://en.wikipedia.org/wiki/UNIX_System_V

on BSD: http://en.wikipedia.org/wiki/Berkeley_Software_Distribution

[nostrademons]

Also, the ascendancy of Linux was a direct result of the fight between them. There was already a perfectly decent free UNIX - BSD - when Linux came out. However, the license wars meant that many corporations wouldn't go near it, because they weren't sure whether they'd get in legal trouble for it or if it would still be available once the lawsuits settled. Rather than deal with that uncertainty, people started looking at Linux as a completely free, from-scratch implementation.