This document provides an introduction to different types of operating systems, including serial processing systems, batch operating systems, multi-programming systems, time sharing systems, distributed systems, network systems, and real-time systems. It defines each type and provides one or two examples. Serial and batch systems execute jobs sequentially while multi-programming systems allow multiple programs to run simultaneously. Time sharing systems rapidly switch between programs to give the appearance they are running simultaneously. Distributed and network systems connect multiple processors across a network. Real-time systems have strict time constraints and do not tolerate delays.