The core piece of software which is described as life of computer system and where the application runs is called Operating System or Kernel. This is an integral part of network servers, desktops, mobile devices, which makes the system controllable, operational and manageable of all the applications and programs. The security of an operating system has an essential impact on the whole computer system as it plays an important role in every computer systems operation. The continuous running of multiple applications on a single operating system software use same resources as CPU, I/O devices, memory and disk. All these components of computer are controlled by the operating system. Security of operating systems include maintenance of confidentiality, availability and system integrity. To make the environment stable, to provide control access to resources and to give external control access to the environment, securing of operating system is necessary. Maintaining physical security of the system, providing security to the information the system holds and securing the network in which it operates are the major kinds of security provided to operating system. In conclusion, the security of operating system plays major role for securing all multiple applications and programs as technology evolves.