Inside Operating System

Inside Operating System
An Operating System is the software that controls the operation of a computer, directs the input and output of data, keeps track of files, and controls the processing of computer programs.
Its roles include managing the functioning of the computerhardware, running the applications programs, serving as an interface between the computer and the user, and allocating computer resources to various functions. Through a process called time-sharing, a large computer can handle interaction with hundreds of users simultaneously, giving each the perception of being the sole user.
When several jobs reside in the computer simultaneously and share resources (multitasking), the OS allocates fixed amounts of CPU time and memory in turn or allows one job to read data while another writes to a printer and still another performs computations.
Operating systems offer a number of services to application programs and users. Applications access these services through application programming interfaces (APIs) or system calls. By invoking these interfaces, the application can request a service from the operating system, pass parameters, and receive the results of the operation.
For hand-held and desktop computers, the GUI is generally considered part of the operating system. For large multiuser systems, the GUI is generally implemented as an application program that runs outside the operating system.