Before Windows was created, the most usual operating system that ran on computers was DOS (Disk Operating System).

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I can remember learning how to use DOS and still use it on a regular basis.

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Over time, newer versions of Windows were developed, and DOS was finally phased out with Windows ME. However, even with Windows 7, 8, 10, and 11, the CMD (Command Line) in DOS (disk operating system) system still runs in the background, and a command line or command prompt window can still be opened. It has a similar appearance to DOS and can be a useful tool when diagnosing problems.

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The command prompt/line is also used in Linux operating systems and many seasoned computer users use the command line as much as the graphical user interface.

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Whether you are using MS Windows, macOS or Linux, there is a Shell, (Shell is a computer program that presents a command-line interface that allows you to control your computer using commands entered with a keyboard instead of controlling graphical user interfaces (GUIs) with a mouse/keyboard combination), Console window or the likes lurking in the background. Windows and Linux use different commands to access and use these Shells, so if you use both you will need to learn two types of command language.