What is the most efficient way to sum up an operating system's core functions?

If you had to compile a list of all the parts that go into the kernel of a standard operating system, how would you sum up the functions of each part?

If you were forced to construct a list of all of the components that make up the kernel of a standard operating system, how would you explain what role each component plays?

What general principle is used in the process of creating the microkernel of an operating system? What do you think is this method's most significant difference from the modular approach?