An operating system is a software program that helps the user interact with a computer. The operating system gives you an interface, or what comes between you and the computer. When you look at your computer screen and all you see is a letter with some funny symbols along with it, such as: c:\>, you are using a command line interface. A command line interface means you must type in what you want your computer to do, (what we call the command), and you must type it correctly. DOS and UNIX are both command line operating systems. (although they do both have graphical interfaces avaialable). Command line operating systems are very efficient in the hands of a skilled user, but they are utterly bewildering to a novice. When you are faced with a command line, you have to know what you want to do, exactly what to type, and you may even have to have special training to understand what it tells you back! Command line operating systems are easy to create, and do not require much from the computer. Earlier machines had command line systems, but as you might guess, not everyone enjoyed them.