A true kernel

The kernel is the heart of any operating system. In some systems, the “kernel” comprises so many functions that for all intents and purposes it is the entire operating system!

But our microkernel is truly a kernel. First of all, like the kernel of a realtime executive, it's very small. Secondly, it's dedicated to only a few fundamental services:

Unlike threads, the microkernel itself is never scheduled for execution. The processor executes code in the microkernel only as the result of an explicit kernel call, an exception, or in response to a hardware interrupt.