There’s a nice article in The Register by Liam Proven, giving an overview of the history of CP/M and what became of it in the days of DOS. And this poses an interesting question: Are all these OSes or at least some of them “CP/M derivatives” covered by the CP/M open licence agreement?
Via HN, discussion: https://news.ycombinator.com/item?id=32411153
My understanding is as follows: when a copyright work is extended, the new additions are copyright too, but not necessarily covered by the same license - unless the original license insisted on it, as the GPL does. So, for example, Amstrad’s PCW version of CP/M might be derived from something now open source, but that doesn’t make it open source - unless it happened to be licensed in that way.
I’d say, this sounds pretty reasonable. There is no way DR could have a say in third party copyrights that came after the initial work, unless there’s a special clause in the license agreement. (Of course, I don’t know anything about these license agreements.)
Having said that, the move by DR could initialize some movement regarding these “derivative” OSes – which is, I suppose, what this articles (which, BTW, provides a decent overview even without this agenda) intends to push a little.