A couple of days back, in a news article titled - Monolithic Kernel vs Micro kernel - published on this blog, I had described the intense debate on this between two school of thoughts fueled by Linus Torvalds and professor Andrew.S.Tanenbaum. One of the examples Andy had given as proof of the stability of micro kernel architecture was the popular Mac OSX itself which (according to Andy) runs on top of the Mach kernel which follows the micro-kernel architecture.
Now it is well known that the Mach micro-kernel, from its inception has been ridden with problems both design wise as well as in performance. So there are many people who wonder why Apple still uses the mach kernel with all its design flaws. In fact there is a group in the Apple community who favor transferring OSX to run on top of the Linux kernel instead which by the way is a monolithic kernel.
Daniel Eran has written an interesting article debunking the popular belief that Mac OSX is based on a micro-kernel architecture and goes on to explain that Apple's kernel named XNU kernel is not implemented as a micro-kernel. In fact, he is of the opinion that the original Mach kernel on which OSX is based on is a fat kernel and it was the Mach micro-kernel project which was a failure.
My Opinion
We are not short of robust kernels be it the BSD kernel, Linux or any other. In fact the beauty of the POSIX environment is that one can switch one kernel for the other and with a little effort still build a stable and secure OS which is what makes this OS design of separating the OS kernel from the userland tools such an exciting proposition.
