First, one should note that this is a chapter (or section) of "The Art of Unix Programming", by esr; it is a fantastic book (I'm going through it now, on chapte

First, one should note that this is a chapter (or section) of "The Art of Unix Programming", by esr; it is a fantastic book (I'm going through it now, on chapter 9 of 20, and the wisdom has been near-palpable). As for the specifics of the article. Plan 9 did indeed do many things right; in fact, many things are done in a very Unixy way. For example, the networking stack is build precisely where it ought to be: as a detail below a powerful network protocol (9P) which can be made as transparent or concrete as necessary (one can easily write individual TCP or UDP packets using the file system; just as easily, you can network-export any file system). Similarly, Plan 9's handling of security, in particular the elimination of the superuser, was fantastic. And while I in particular disagree with the approach Plan 9 takes to the GUI, it is certainly a consistent, powerful, and inspired model. And a variety of its other ideas, such as UTF-8 and the /proc and /sys file systems, have worked their way into modern Unixes such as Linux. Now, Plan 9's failure has been aptly explained elsewhere, in particular in the article linked. But, being somewhat old (2004, I believe; though when that particular section was written I do not know), it makes the prediction that Unixes will eventually come to absorb all of the Plan 9 features. Instead, it looks like the Linux kernel, at least, has mostly given up on ever implementing union mounts (one of the most inspired of Plan 9's innovations, at least in my view). And while the /net file system is incredibly useful, its power is much diminished when you can't assume that the world speaks 9P, which will seemingly never be the case. And a variety of Plan 9's choices are impossible without ignoring POSIX compatibility, which causes problems of its own. Unix rode the growth of servers in the seventies and eighties, and is by now rather entrenched (see the History chapter in Art of Unix Programming); much like the WIMP GUI metaphor rode the personal computing wave. I think both of these areas are by now too old and entrenched for us to simply replace the current monopolies there. And I've come to terms with the fact that Plan 9 will never, ever become the standard OS --- it is simply not designed for any battlegrounds except those it has already lost in. But I strongly urge anyone designing an OS (or, really, any sort of all-encompassing computer system) to look over the innovations and ideas of Plan 9. Luckily, I don't think anything like Windows or Unix will win in a totally new environment, because Windows and Unix aren't made for any environments but their own. So while Plan 9 never won, I think its ideas have a good chance of living on. And I await an exciting time of innovation in Operating Systems in the coming century.