This document provides information about operating systems including definitions, functions, types, and user interfaces. It defines an operating system as a set of programs that controls computer resources and provides an interface for users. Popular operating systems mentioned include Unix, MS-Dos, Windows, and Linux. The document describes types such as real-time, single-user single-tasking, single-user multitasking, and multi-user multitasking operating systems. Functions of operating systems include displaying elements, loading programs, coordinating hardware/software, and managing data storage. User interfaces are described as either graphical or command line.