While RAM is a form of computer storage, you must always remember that it is temporary, or working memory. This means that any information that is not saved, whether to hard drive or disk, will not remain in RAM once the computer is turned off. Also, standard RAM on newer computers is usually between 32 and 64 megabytes. This CAN get filled up. When it does, your computer may crash and all unsaved info WILL be lost.
Operating systems are a form of software that makes the computer operable by the user.
The operating system is an interface which facilitates user access to storage, software and peripherals. This is a character-based system in which the user types commands at a prompt displayed on the screen. MS-DOS is an example of a Command Line Operating System. Menu interfaces are easier to operate than command line systems but are still character-based. Users only have to choose from a list of operations, sometimes a mouse can even be used.