what is the kernel of the operating system; hybrid kernel, monolithic kernel, microkernel.
iMac, Mac OS X (10.0.x)
Carnegie Mellon MACH micro kernel with FreeBSD Unix APIs and utilities as a starting point, which has then been evolved.
The XNU kernel that's used underneath Mac OS X, iOS and Darwin is a hybrid kernel, and neither a microkernel nor a monolithic kernel design.
The XNU design does have features of the Mach kernel; that's why it's a hybrid. (Pedantic: It's "Mach" and not "MACH", FWIW.)
If this isn't a one-off computer-class homework question (that's the usual source of this "what sort of kernel is the [whatever] operating system?" question that's been circulating around in the curriculums of computer-related programs for decades) and you're seeking to learn more about Mac OS X and its XNU kernel innards, then you'll want to acquire a copy of Amit Singh's Mac OS X Internals book, and start reading.
Google is your friend here, too; that's often a far faster path to answers such as this one.
How the kernel works in Mac osx, what type of kernel, memory manager, IPC etc
