Operating System
1
An operating system (OS) is the master control software program required in order for a
general-purpose computer to function [1]. It manages all of the computer’s software and
hardware [2]. For example, it allows the user to communicate with the hardware by, among
other methods, entering input into the keyboard and receiving output on the screen. It also
acts as a “traffic cop” to make sure each application (non-operating-system program) gets the
hardware resources it needs without interfering with another application [3].
The operating system comes preinstalled on the computer. It launches when the computer is
turned on, runs in the background, and stays on until the computer is turned off.
This discussion describes the essential operations that operating systems perform: how
users and applications communicate with the OS; types of OSs; and examples and market
share of common OSs.
Operating System Tasks
The operating system performs a number of essential operations, including:
• Receiving input from the user via input devices such as the keyboard, mouse or
touchscreen.
• Sending output to an output device such as the screen or printer.
Note: Operations such as these are input/output operations or I/O.
• Controlling other peripheral devices (auxiliary devices connected to the computer) such as
disk drives, scanners, cameras, and microphones.
Note: Peripheral devices are also I/O devices.
• Managing access to hardware resources, specifically, the central processing unit (CPU, the
“brain” of the computer), memory, and storage.
• Establishing a user interface.
• Managing files and directories (sometimes called folders).
• Communicating with a computer network.
• Allowing access only to authorized users.
Communication with the Operating System
Users and applications communicate with the operating system in order to make requests
and receive results.
User interface. Users interact with the operating system through either a command line
interface (CLI, sometimes called a shell), which accepts text commands and displays output
1
The audience for this extended definition is made up of marketing professionals new to the computer field and
needing background information on how computers work. They are college educated and familiar with using
desktop computers and mobile devices, but typically without an understanding of what goes on “under the hood.”
