What is OS (Operating System)?

Updated: 02/01/2021 by Computer Hope

Windows XP

An operating system or OS is a software installed on a computer’s hard drive that enables the computer hardware to communicate and operate with the computer software. Without a computer operating system, a computer and software programs would be useless. The picture shows Microsoft Windows XP in its original packaging.

When computers were first introduced, the user interacted with them using a command line interface, which required commands. Today, almost every computer uses a GUI (Graphical User Interface) operating system that’s easy to use and operate.


Some people may refer to an OS as “operating software.” Although this is a valid term, it is more appropriate to refer to this software as an “operating system.”

Examples of computer operating systems

Below is a list of examples of different computer operating systems over the evolution of computers.


The following operating systems are considered GPOS (general purpose operating systems). See our RTOS (real-time operating system) definition for examples of RTOS.

Microsoft Windows

Microsoft Windows is the most common and used operating system on computers today, with Microsoft Windows 10 being the most recently released version of Windows. The operating system is used PC and IBM compatible computers.

Apple macOS

With Apple computers, macOS is the primary operating system used with Apple desktop and laptop computers.


Linux is a free and open source operating system used with PC and IBM compatible computers. Because the operating system is open source, it is used to create many variants of Linux, including Ubuntu, Debian, Red Hat, and Slackware. See our Linux page for a full listing of variants listed on our site with further information about the operating system.

Chromium / Chrome OS

Chrome OS is an operating system used with Google Chromebooks.

Mobile operating systems


Android in an operating system used with smartphones and tablets. Today, Android is the most popular operating system worldwide because of how many smartphones use a variant of the Android operating system.

Apple iOS

The Apple iOS operating system used is the operating system used with the Apple iPhone and iPads.

Other operating systems

The following list contains operating systems that either do not fit into the previous categories or are considered legacy.

Where is the operating system stored on a computer?

With most computers, the operating system is stored on the primary hard drive inside the computer. Computers operating systems can also be installed and loaded from an external hard drive, disc drive, or flash drive.

When installing the operating system the install files are stored on a CD, DVD, or USB flash drive. Early computer operating systems used multiple floppy diskettes to install an operating system.

What is the history of operating systems?

Over the history of computers there have been many operating systems and versions. To help make going through the history of operating systems easier we’ve broken the computer operating system history into the following pages.

Command line, Computer acronyms, Embedded operating system, GUI, Microsoft, NOS, Operating environment, Operating system terms, RTOS, System software, TOS


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