An operating system (OS) is the software that manages the sharing of the resources of a computer. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking and managing file systems. Most operating systems come with an application that provides a user interface for managing the operating system, such as a command line interpreter or graphical user interface. The operating system forms a platform for other system software and for application software. Linux and Mac OS (or any other BSD-derivative) are popular UNIX-like operating systems. Windows takes a different approach to operating systems, derived upon a historic single-user model.
Links:
http://en.wikipedia.org/wiki/Operating_system
http://computer.howstuffworks.com/operating-system.htm
http://www.top500.org/lists/2005/11/charts/Operating_System
