1.2 Overview of Computer Operating Systems
1.2.1 Desktop operating systems
All computers require an operating system (OS) to manage their functions, regardless of the manufacturer and whether it is a micro, midrange or mainframe computer. Operating systems can be divided into two major categories: single user or desktop and multi-user or network. Most desktop operating systems are single user, meaning they can only keep track of what one user is doing at a time. DOS and Windows 3.x are examples of single user desktop operating systems since the activities of only one user can be managed or only one user can be logged in at a time. Windows 9x, NT Workstation, Windows 2000, and Mac OS have some networking capabilities for peer-to-peer workgroup networking, but they are largely considered desktop operating systems.

UNIX can also serve as a desktop operating system but is primarily for use with high-end workstations. Examples of these include engineering and scientific applications which require dedicated high-performance workstations. Specific applications include Computer Aided Design (CAD), electronic circuit design, weather data analysis, computer graphics and animation, and medical equipment consoles.