IBM i opened my eyes a bit, and made me a bit sad, when I decided to check it out after decades of working on what I now realize are entirely UNIX-y OSes. By th

IBM i opened my eyes a bit, and made me a bit sad, when I decided to check it out after decades of working on what I now realize are entirely UNIX-y OSes. By that I mean that besides the many actual UNIX-derived systems like Linux, Solaris, HP/UX, macOS I worked on, IBM i made me realize that DOS, Windows, OS/2, and whatever else most people are probably aware of nowadays, are also UNIX clones to a much higher degree than I thought. IBM i is completely different in many ways. It has a unified 128bit address space. It does not have the same concept of a hierarchical filesystem (by default, you can bolt one on, but it clearly does not "fit"), and it does not even strongly have the concept of having everything in "streaming" files (or their equivalent) to begin with. It also has a completely different "command line" concept for example, and countless other aspects that are hard to explain succinctly. It is a bit like learning Haskell, where it used to feel like you thought you could learn every language in an afternoon (after C, C++, Java, JS, Pascal, perl, python, awk, shells, BASIC, and countless others), but then discover you have to relearn the very basics, and that what you thought of as universal actually isn't. A lot of these concepts work really well. They are at a level of abstraction that I would not have thought possible in practice. They allow the system to be incredibly stable and low maintenance, and elegant. The underlying architecture was changed at least once (maybe twice, not sure), and it was entirely seamless for customers. It made me sad because I discovered a computing world that could be widespread reality, but in all likelihood won't be. That's thanks to UNIX being so pervasive that it's now basically woven into the very fabric of computing, but that is of course in no small part thanks to IBM's extreme closeness. I once thought UNIX was the way to go, but I'm not so sure anymore. And now that it's everywhere, too many of its concepts are considered a "ground truth". UNIX won because it was hard to avoid getting exposed to it, while for IBM i you had and still have to fight for even just trying it out. Interestingly, the IBM mainframe world, i.e. z/OS and its predecessors, do feel the same in terms of "you have to relearn everything", but with the opposite outcome. Where IBM i is presenting you with unique abstractions from the very base of the OS, it's amazing how little abstraction there is in the mainframe world. You clearly get a sense that mainframes come from a time where a lot of common concepts simply had not been invented yet, while on the other hand IBM i (or rather its predecessors) reimagined OSes at a much later time.