An 'operating system' (commonly abbreviated OS and O/S) 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 operating system acts as a host for applications that are run on the machine. As a host, one of the purposes of an operating system 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, including handheld computers, desktop computers, supercomputers, and even video game consoles, use an operating system of some type. Some of the oldest models may however use an embedded operating system, that may be contained on a compact disk or other data storage device.

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. Users may also interact with the operating system with some kind a software user interface (UI) like typing commands by using command line interface (CLI) or using a graphical user interface (GUI, commonly pronounced “gooey”). For hand-held and desktop computers, the user interface is generally considered part of the operating system. On large multi-user systems like Unix and Unix-like systems, the user interface is generally implemented as an application program that runs outside the operating system. (Whether the user interface should be included as part of the operating system is a point of contention.)

Common contemporary operating systems include Microsoft Windows, Mac OS, Linux and Solaris. Microsoft Windows has a significant majority of market share in the desktop and notebook computer markets, while servers generally run on Linux or other Unix-like systems. Embedded device markets are split amongst several operating systems.

Technology

An operating system is a collection of technologies which are designed to allow the computer to perform certain functions. These technologies may or may not be present in every operating system, and there are often differences in how they are implemented. However as stated above most modern operating systems are derived from common design ancestors, and are therefore basically similar.

Program execution

main: Process (computing) Executing a program involves the creation of a process by the operating system. The kernel creates a process by setting aside or allocating some memory, loading program code from a disk or another part of memory into the newly allocated space, and starting it running.

Interrupts