An operating system (OS) is the software component of a computer system that is responsible for the management and coordination of activities and the sharing of the resources of the computer. The OS acts as a host for application programs that are run on the machine. As a host, one of the purposes of an OS is to handle the details of the operation of the hardware. This relieves application programs from having to manage these details and makes it easier to write applications. Almost all computers use an OS of some type. OSs offers a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By using these interfaces, the application can request a service from the OS, pass parameters, and receive the results of the operation. Users may also interact with the OS by typing commands or using a graphical user interface (GUI). By any standard of measure, an operating system is the most critical software installed on a computer. Not only does an operating system act as the administrator of many computer processes, but it also allows users to harness the power of the various sound, graphics and memory assets within the computer’s hardware infrastructure. For the vast majority of users today, a computer would be useless if it did not include some form of an operating system.