This document provides an introduction to operating systems. It defines an operating system as low-level software that enables interaction between a user, application programs, and a computer's hardware. An OS performs basic tasks like input/output management and running programs. It also provides services for program execution, I/O operations, and communication between processes locally or across networks. The choice of OS determines the applications that can be run. Examples of operating systems mentioned are Windows, DOS, Linux, Mac OS, and others.