An operating system enables application programs to be executed and acts as an communication bridge (interface) between the user and the computer hardware.
The main task of an operating system is the allocation of resources and services, such as allocation of: memory, devices, processors and information. The operating system also includes programs to manage these resources, such as a traffic controller, a scheduler, memory management module, I/O programs, and a file system.
The important functions of an operating System are:

• Security -
  The operating system uses password protection to protect user data and similar other techniques. it also prevents unauthorized access to programs and user data.
• Control over system performance -
  Monitors overall system health to help improve performance. records the response time between service requests and system response to have a complete view of the system health. This can help improve performance by providing important information needed to troubleshoot problems.
• Job accounting -
  Operating system Keeps track of time and resources used by various tasks and users, this information can be used to track resource usage for a particular user or group of user. Error detecting aids -
  Operating system constantly monitors the system to detect errors and avoid the malfunctioning of computer system.
• Coordination between other software and users - Operating systems also coordinate and assign interpreters, compilers, assemblers and other software to the various users of the computer systems.
• Memory Management -
  The operating system manages the Primary Memory or Main Memory. Main memory is made up of a large array of bytes or words where each byte or word is assigned a certain address. Main memory is a fast storage and it can be accessed directly by the CPU. For a program to be executed, it should be first loaded in the main memory. An Operating System performs the following activities for memory management:

  It keeps tracks of primary memory, i.e., which bytes of memory are used by which user program. The memory addresses that have already been allocated and the memory addresses of the memory that has not yet been used. In multi programming, the OS decides the order in which process are granted access to memory, and for how long.
  It Allocates the memory to a process when the process requests it and de-allocates the memory when the process has terminated or is performing an I/O operation.

• Processor Management -
  In a multi programming environment, the OS decides the order in which processes have access to the processor, and how much processing time each process has. This function of OS is called process scheduling. An Operating System performs the following activities for processor management.
  Keeps tracks of the status of processes. The program that performs this task is known as traffic controller. Allocates the CPU that is processor to a process. De-allocates processor when a process is no more required.
• Device Management -
  
  • An OS manages device communication via their respective drivers. It performs the following activities for device management.
  • Keeps tracks of all devices connected to system. designates a program responsible for every device known as the Input/Output controller.
  • Decides which process gets access to a certain device and for how long. Allocates devices in an effective and efficient way.
  • Deallocates devices when they are no longer required.
• File Management -
  A file system is organized into directories for efficient or easy navigation and usage. These directories may contain other directories and other files. An Operating System carries out the following file management activities. It keeps track of where information is stored, user access settings and status of every file and more. These facilities are collectively known as the file system.