OPERATING SYSTEM (OS)

Operating System or OS is the system software responsible for the control and management of hardware and basic operations systems, including software applications running programs like word processors and web browsers.
In general, the Operating System software on the first layer is placed on the computer's memory when the computer boots. While other software is run after the operating system running, and OS will make public the core services for the software. Common core services such as access to the disk, memory management, skeduling task, and user interfaces. So that each software no longer need to perform the core duties of the public, because it can be served and performed by the operating system. Section of code that perform the core duties and the public is called the "kernel" of a Operating System
If the computer system divided into layers, then the Operating System is the liaison between the layers of hardware and software layers. Further than that, Operating System do all essential tasks in the computer, and ensure that applications can run different simultaneously smoothly. Operating System ensure other software applications can use the memory, perform input and output of other equipment, and have access to the file system. If several applications running simultaneously, then the operating system appropriate arrangements, so far as possible all the processes running to get enough time to use the processor (CPU) and do not interfere with each other.
In many cases, operating system provides a library of standard functions, which other applications can call functions, so that in every creation of new programs, no need to create these functions from scratch.
Operating systems generally consist of several parts: 1. Boot mechanism, which is putting the kernel into memory
2. Kernel, which is the core of an Operating System
3. Command interpreter or shell, which served to read input from the user
4. Library-library, which provides a collection of basic functions and standards that can be called by other applications
5. Drivers to interact with external hardware, as well as to control them
Some operating system only allows one application are running at one time (eg DOS), but most of the new operating system allows several applications running simultaneously at the same time. Operating systems like this is called the Multi-tasking Operating System (eg the UNIX operating system families). Some Operating Systems are very large and complex, and its inputs depending on the user input, while the other Operating Systems is very small and made with the assumption that work without human intervention at all. The first type is often referred to as a Desktop OS, while the second type is the Real-Time OS