In general, the Operating System software is the first layer is placed on the computer memory when the computer starts. While other software is run after the OS is running, and the Operating System will perform the core public service for the software. Core public services such as access to the disk, memory management, task scheduling, and user interface. So that each software does not need to perform tasks common core, as can be managed and conducted by the Operating System. The code of tasks and common core is called the "kernel" of an Operating System.
translation of: http://id.wikipedia.org/wiki/Sistem_operasi