Apple Darwin (which is the OS X kernel) is a hybrid of the Mach microkernel, and the FreeBSD 5.x monolithic kernel as well as some proprietry programming from Apple. The bulk of the kernel is based on FreeBSD 5.x, although they've pulled components from Mach where FreeBSD 5.x lacks, such as the IPC (Inter-Process-Communication) and a few small components. FreeBSD is a very powerful kernel, and is used in many server enviroments, and even desktop/workstation enviroments. It's also widely popular in cluster-type enviroments, and SMP enviroments. With your non-existant knowledge of basic computing terms, I feel it neccesary to explain to you what SMP means. SMP stands for Symmetrical Multi Processing. In order to take advantage of SMP, the kernel must be able to handle multiple threads, or "applications" in idiot speak.
I really don't think it's neccesary to explain to you how BSD-based systems handle SMP and multiple threads, since:
A. I don't think you'd understand 1/10th of it, and...
B. I really don't have the time to explain to such a low form of life.
But I can gladly tell you than WindowsNT 5.x is pathetic at multithreading. Please don't argue with me, I've been using BSD for eight, count them EIGHT years and I've had more than enough experience with both Windows and BSD systems to know which one performs better in a variety of situations. If you want to argue, please get a copy of FreeBSD 5.3 (the basis of current Mac OS X systems), Windows 2003 (it's the latest released Windows NT kernel, and is the most scalable), a system that can handle many threads, and do some benchmarks whilst running some CPU hogging processes in the background.