AnandTech: No more mysteries: Apple's G5 versus x86, Mac OS X versus Linux

AnandTech: No more mysteries: Apple's G5 versus x86, Mac OS X versus Linux: "Darwin is indeed the open Source project around the Mach kernel 3.0. This operating system is based around the idea of a microkernel, a kernel that only contains the essence of the operating system, such as protected memory, fine-grained multithreading and symmetric multiprocessing support. This in contrast to 'monolithic' operating systems, which have all of the code in a single large kernel.

Everything else is located in smaller programs, servers, which communicate with each other via ports and an IPC (Inter Process Communication) system. Explaining this in detail is beyond the scope of this article (read more here). But in a nutshell, a Mach microkernel should be more elegant, easier to debug and better at keeping different processes from writing in eachother's protected memory areas than our typical 'monolithic' operating systems such as Linux and Windows NT/XP/2000. The Mach microkernel was believed to be the future of all operating systems.

However, you must know that applications (in the userspace) need, of course, access to the services of the kernel. In Unix, this is done with a Syscall, and it results in two context switches (the CPU has to swap out one process for another): from the application to the kernel and back.

The relatively complicated memory management (especially if the server process runs in user mode instead of kernel) and IPC messaging makes a call to the Mach kernel a lot slower, up to 6 times slower than the monolithic ones!

It also must be remarked that, for example, Linux is not completely a monolithic OS. You can choose whether you like to incorporate a driver in the kernel (faster, but more complex) or in userspace (slower, but the kernel remains slimmer). "