An operating system is a system software which acts as an interface between a computer user and computer hardware. The purpose of an operating  system is to provide an environment in which a user can execute  programs in a convenient and efficient manner. Since  an operating system is large and complex, it must be created  piece by piece. Each of these pieces should be a well-delineated portion of the  system, with carefully defined inputs, outputs, and functions. Ex:- Unix, Linux, MS Dos, macOS, windows, android etc.   *   Important functions of an operating System:-   1>  Memory Management.   2>  Processor Management.   3>  Device Management.   4>  File Management.   5>  Security providing.   6>  Job accounting.   7>  Control over system performance.   8>  Error detection.   9>  Coordination between other softwares. 1. Memory Management:-   The operating system manages the Primary Memory or Main Memory.  An operating system