The Mac OS X kernel is based on Mach and FreeBSD. It means that it is microkernel. In the world of academics - where people usually dream about computers rather than use them - microkernel is good, because it provides a flexibility of linking and unlinking kernel extensions without having to restart the computer. And it saves memory too. However, in the real life, where we write serious software, there is something called “Process switching”, which is the switching between Kernel mode and User mode processes. And microkernel is damn slow at process switching. For that reason, the only commercial system that has microkernel is Mac OS X…