1. If Shell is something that handles the commands, what is the Operating System them? What does that do actually? Bridge the Shell and the Hardware or Instruction Set together?

2. One of the commands that I'm curious about is the "which" command. I want to know what is exactly written inside it. How will I know that?

3. I've just read that Windows Explorer is the Shell for most Windows OSes. Does Vista have the same shell too?

4. If both Linux and Windows were built on Unix, what is it that differentiates them the most? Why are only a few unix commands retained in Windows?

5. If Windows Explorer is a shell, then what is a Kernel?