> Mac OS came from Mach I believe you mean OS X, not MacOS. Apple could switch OS X to entirely proprietary underpinnings and few customers would even notice.

> Mac OS came from Mach I believe you mean OS X, not MacOS. Apple could switch OS X to entirely proprietary underpinnings and few customers would even notice. In fact, OpenStep ran just fine on top of NT. [And also on top of then-non-open Solaris]. https://en.wikipedia.org/wiki/OpenStep https://en.wikipedia.org/wiki/OpenStep