OS X is not a microkernel and hasn't been one since 10.0. It is a hybrid kernel called the XNU kernel. It's Mach microkernel based with some low layer BSD smothered on top.
It would be interesting to see how the original Mach microkernel runs on modern hardware. At the time, the context switching of the Mach kernel was making performance poor. But this was on 300/400 MHz machines.
It would be interesting to see how the original Mach microkernel runs on modern hardware. At the time, the context switching of the Mach kernel was making performance poor. But this was on 300/400 MHz machines.