The people over at IBM have created a nice overview of the various components of the Linux kernel. The article gives a quick history of Linux and then moves on to explain the various parts existing in the Linux kernel. The article has been written to give a better understanding of the structure of the over five million lines of source code the kernel consists of. There are a also number of very useful links at the end of the article to more in-depth resources about various parts of the kernel.
The Linux® kernel is the core of a large and complex operating system, and while it's huge, it is well organized in terms of subsystems and layers. In this article, you explore the general structure of the Linux kernel and get to know its major subsystems and core interfaces. Where possible, you get links to other IBM articles to help you dig deeper.