If you used code that was derived from AT&T’s Intellectual property, you could only share that with others that had the same license.  But a developer has always been free to share anything they owned, although traditionally before sharing you add a copyright and simple terms of usage license – a.k.a. the CMU/MIT/UCB (– sometimes called the Dead Fish style License). So if you wrote something original, you as the author could and did do what you wanted with it and traditionally most Unix developers gave it away to other users to use – consider any of the tools that came out of Harvard, Purdue, CMU, MIT, UCB et al – e.g. CMU Emacs, and UCB Pascal,  GCC ; the list is quite long.

Another way to think of this say – since the Universities were using Unix as a research tool, they could and did use Unix for as they wished, but they could not give out the AT&T derived Unix technology.

In order to get a copy of AT&T Unix at the time, Universities had to pay a $100 license fee to AT&T and
the source code was delivered on a magnetic tape (”abandoned on your doorstep” as it was sometimes referred). The problem with this
model is that you could not legally share source code that was ported from
Unix derived technology unless the recipients had their own license.

Cole revealed some intricacies related to the discrepancies between AT8T Unix and BSD Unix:

UCB, like many research users using Unix made a distribution of it’s tools and modifications – BSD – Berkeley Software Distribution. Numerous Berkeley distributions were made over time, and since all were based on the AT&T technology, to get a copy of BSD you needed to be show that you too possessed an AT&T Unix licensee.

Originally, BSD Unix could be licensed by any institution (research or commercial actually) that could demonstrate they had an AT&T license.  It was just easier to check for that license since “everyone” could get one (although commercial users paid more to AT&T). Remember, the cost of the hardware to use the AT&T code was at minimum $100K and often 5 or 10 times that.  So
the $100 for an AT&T license for a University was peanuts, and cost to UCB were equally small to pay for the duplication etc.

Note that at that time… the owner of the code would add a copyright
and a “license” to the top the file, and the different license were created to solve different issues.  The non-viral “dead-fish” style used by UCB is probably the longest-lived and basically says something like:  Hey we wrote this.  Use it at your own risk – i.e. don’t try to collect damages. If you do anything with it, you have to mention it came from us originally, but you can do what ever you want with it”  – i.e. wrap dead fish in it for market, make a product with it, study it, etc – have fun.

Over the course of a number years and after many different BSD releases, Berkeley’s team said, “hang on” – very little of what is now in BSD is based on AT&T’s code.  So a number of folks at UCB began to make two piles of code in BSD depending on the “providence” (“AT&T derived – a.k.a. tainted” and “non-AT&T – a.k.a. clean” code).   Eventually the non-AT&T owned pile was nearly the entire set.   So, the UCB Team eventually released as the BSD NET2 distribution (the non-AT&T version) and it was made available to anyone – you only needed to obey the licenses and copyrights in the code itself.  All of this occurs during this time, when BSD was being ported to more and more systems other than the original VAX system it was designed for – such as the Sun2, 386, etc.

Once NET2 was released, some of the developers formed a company called BSD, Inc.  The BSD Inc. folks then started with NET2 and add the “missing” parts that they wrote themselves and created an “open source” “product” for Intel based PC’s running 386’s and 486s – called BSDi.

Shortly thereafter AT&T sued both BSDi and UCB for improper use of their IP.   UC Berkeley & BSDi eventually won the case, although I believe the court forced a handful more of files to be removed from NET2”

Us hacker types thought the AT&T/UCB case was about copyright.  It turns out it was not.  The case was about trade secrets – which is much more serious.   In fact, we were later told that if AT&T had won, any Unix/POSIX-like system is a derivative of the ideas used to build Unix – not just system built using AT&T based source code.  This means any Unix-like system would have to been not allowed – not just BSD.  If this definition had come into play, it would been that any Unix or POSIX system would an “AT&T derivitive work.”  Which to modern users it would have meant that not only BSD but Linux [and Minux, et al] would have to been licensed from AT&T to be made available for use.

According to Cole, “A user would obtain the source, then modified the software, and then fed the modified version back into the community.” It is a model that has pioneered some of the greatest and widely adopted software projects to do date, many of them incubated on Unix or Unix-like systems. To this day, this practice continues – but at a scale never before imagined.