Yes, AS/400 / IBM i is the other IBM OS I like to play with (I have an actual AS/400e at home), and in a lot of ways I consider it to be the polar opposite of M

Yes, AS/400 / IBM i is the other IBM OS I like to play with (I have an actual AS/400e at home), and in a lot of ways I consider it to be the polar opposite of MVS on the mainframe: Where MVS seems to be missing very simple abstractions that I took for granted, AS/400 abstracts way more than I'm used to, differently, and most importantly far away from the very, very "file-centric" view of today's systems that was derived from UNIX. It indeed shows you what computing could have been, had AS/400 been more open and had those ideas spread farther. Before I got to know AS/400, I thought UNIX was great, and that it rightfully took over computing. Now, not so much, and I've started to see how detrimental the "everything is a file" concept that UNIX brought into the world actually was to computing in general.