 An operating system (OS) is a set of computer programs that allow the user to perform basic tasks like copying, moving, saving and printing files.  It also provides an interface (communication) between applications program (e.g. wordprocessors or spreadsheets) and the computer hardware.  The work of the operating system takes place in the background and it is not always obvious to the user.

 Command-driven – user runs a program by typing a command. The screen is usually blank except for a symbol (e.g. >_) which is a command prompt.

 GUI - graphical user interface, that allows the user to use a mouse to click on icons on the screen or choose commands from a list of choices known as a menu.

Work in groups: Make a list of operating systems you know.

 DOS,  Microsoft Windows,  UNIX,  Linux,  iOS,  Mac OS X,  Android.

 In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands.  GUIs can be used in computers, hand- held devices such as MP3 players, portable media players or gaming devices, household appliances and office equipment.