Every computer has an operating system and every operating system performs a variety of functions. These functions can be lassified into three groups:
* Managing resources: Operating systems coordinate all the computer's resources including memory, processing, storage, and devices such as printers and monitors. They also monitor system performance, schedule tasks, provide security, and start up the computer.
* Providing user interface: Operating systems allow users to interact with application programs and computer hardware through a user interface.Many older operating systems used a character-based interface in which users communicated with the operating system through written commands such as "Copy A: assign.doc C:". Almost all newer operating systems use a graphical user interface (gui). As we discussed in Chapter 3, a graphical user interface uses graphical elements such as icons and windows.