An operating system (commonly abbreviated to either OS or O/S ) is an interface
between hardware and user; it is responsible for the management and coordination of
activities and the sharing of the limited 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 of 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,
BSD and Solaris. Microsoft Windows has a significant majority of market share in the
desktop and notebook computer markets, while servers generally run on Unix or Unix-
like systems. Embedded device markets are split amongst several operating systems.
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