Operating systems as a resource manager

An operating system is an organized set of hardware extensions consisting of control programs that operate a computer and provide a program execution system. Other programs use the facilities provided by the operating system to access computer system resources, such as files and input/output (I/O) devices. Programs usually invoke active system services by calling the environment. In addition, users can directly interact with the active system using commands. In both cases, the active system acts as an interface between the user and the computer system hardware. Internally, the operating system acts as a manager of system resources such as processors, memory, files, and input/output devices. In this role, the operating system monitors the state of each resource and determines who gets the resource and when. In systems that support concurrent program execution, the operating system resolves conflicting resource requests in a manner that preserves system integrity in an effort to maximize performance.