> Is this why nothing has really come from Mach/Hurd? Mach 3.0 was the kernel used in NeXT and the original Mac OS X release. It was quite a bit later replaced

> Is this why nothing has really come from Mach/Hurd? Mach 3.0 was the kernel used in NeXT and the original Mac OS X release. It was quite a bit later replaced with a rewritten kernel XNU, that’s basically a hybrid. The reason as I understand it, message passing in the kernel is expensive when crossing user space so often. I wouldn’t call that nothing coming of Mach, it did really well! Also, I’d say that micro-kernels are closer to the paradigm of react/redux (redux the message bus, react the user space servers) than to a monolith design like Linux.