There is nothing astronaut-ty or theoretical about microkernels. For eg, QNX is a fairly successful, practical microkernel, its what your BlackBerry runs on. If

There is nothing astronaut-ty or theoretical about microkernels. For eg, QNX is a fairly successful, practical microkernel, its what your BlackBerry runs on. If anything, microkernels are one of the most practical ways to approach OS design. You strip the kernel to its bare minimum and do everything else in usermode via IPC. It so turns out in practice that the performance costs of IPC is much more than making a direct syscall in a monolithic kernel, but that is just today's state of the art. As IPC performance improves & monolithic kernel KLOCs explode, you will see microkernels making a strong comeback, especially on mobile. Wait and see.