Many buzzwords are associated with Mac OS X: Mach kernel, microkernel, FreeBSD kernel, C++, 64 bit, UNIX... and while all of these apply in some way, "XNU", the Mac OS X kernel is neither Mach, nor FreeBSD-based, it's not a microkernel, it's not written in C++ and it's not 64 bit - but it is UNIX... but just since recently.
This talk intends to clear up the confusion by presenting details of the Mac OS X kernel architecture, its components Mach, BSD and I/O-Kit, what's so different and special about this design, and what the special strengths of it are.