What is a command prompt?

A command prompt is a non-graphical interface that allows you to interact with your operating system. At the command prompt, you enter commands by typing their names followed by options and arguments. Most modern computers use a graphical user interface (GUI), which allows users to more intuitively access programs and documents. However, some programs and commands are still only available only through a command prompt. To access the command prompt, follow the instructions appropriate to your operating system.

Windows

To access the command prompt in Windows, from the Start menu, select Run... . In the "Open:" field, enter cmd (Windows NT, 2000, XP, and Vista) or command (Windows 95, 98, and Me).
For information about commands you can use in the Windows command prompt, see What are some examples of common DOS commands?

Mac OS X

Mac OS X is built on a version of Unix called Darwin. To access the Unix command prompt in Mac OS X, open the Terminal application. It is located by default inside the Utilities folder, which in turn is inside the Applications folder.
For information about Unix commands, see Introduction to Unix commands.

Unix

When you log into a Unix computer, your shell begins to run and provides you with a command prompt. The command prompt's appearance varies depending on the shell you're using. For information to help you select a shell, see In Unix, where can I get information on differences between the various shells?
For information about Unix commands, see Introduction to Unix commands.