I disagree with a lot of what you are saying. OSes these days are a lot, a lot, more complex and richer than the "original" old ones. Sure there is some compat

I disagree with a lot of what you are saying. OSes these days are a lot, a lot, more complex and richer than the "original" old ones. Sure there is some compatibility with Posix because it is a nice common factor to start from, and it incorporates some ideas about multitasking and multiuser systems but everything is substantially different. POSIX permissions coexist with ACLs and much stronger security models, code signing, sandboxing, etc.. Compressed memory, copy-on-write, snapshotting filesystems, graphics as a privileged citizen, OS handling of energy efficiency, and so on and so forth... We have long outgrown the "original" OSes and today commercial OSes have a ton of man-hours behind them that make every hobbyist OS pale in comparison. It's not lipstick on old pigs, POSIX is an old lipstick to make the new pigs somewhat compatible with one another.