Chapter 1: Introduction

- monolithic systems ("the big mess"): Linux, Unix;

- layered systems: THE, Multics (protection rings);

- microkernel: implement most of the OS in user space.  A user process
  (client) sends requests to a server process. An advantage:
  adaptability to use in distributed systems;

- microkernel examples: Amoeba, Chorus, Mach, V