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 

                       LINKED LIST    A linked list is non-premitive data structure.  A  linked list  is a way to store a collection of elements. Like an array these can be character or integers. Each element in a linked list is stored in the form of a  node .   And a node is a collection of two sub-elements or parts , information or data part and another is address part .  A linked list is formed when many such nodes are linked together to form a chain. Each node points to the next node present in the order. The first node is always used as a reference to traverse the list and is called  Start or head and t he last node points to   NULL . Arrays can be used to store linear data of similar types, but arrays have some limitations as the size of the arrays is fixed: So we must know the upper limit on the number of elements in advance. Also, generally, the allocated memory is equal to the upper limit irrespective of the usage. Inserting a new element in an array of elem