I find it hard to imagine a world which in a 100 years Unix-derived systems are prevalent let alone running everything from phones to supercomputers. I can't i

I find it hard to imagine a world which in a 100 years Unix-derived systems are prevalent let alone running everything from phones to supercomputers. I can't imagine what would come along, but whatever it is will eventually be just as crufty, because that's just the way of things. What I'd really like to know, what is Unix, at the core. I know POSIX defines certain standards, but what can we rip out and still call what remains Unix? If we're being really reductive can't we take it beyond the features that were present in the very first Unix for the PDP7? Is it simply the syscall interface which provides a filesystem abstraction? Do we call an OS a Unix if it only has a POSIX layer like Windows NT? So if we could strip everything out and leave just a few pieces, and still recognize it as Unix, the use of the word approaches meaninglessness. Unixes exist without memory management or process isolation. Think of how fundamentally dissimilar an Apple Watch running iOS is compared to a PDP11. I think that versatility in the terminology itself lets us keep calling something Unix long after it's morphed into something else. It's not hard to imagine replacing system calls with other ways of achieving the same outcome. I think fundamentally, at the lowest level, where the operating system is an interface to the core features of the processor, it is relatively invariant. For truly unique systems, we do have to look at the hardware. Unique operating systems have been tied to unique hardware, like the Xerox Alto, or the MIT CADR, whereas Unix as a generic set of functionality has made many computer architectures useful, but also reduced their variety.