RAM is cheap and fast compared to some other forms of memory.
RAM is temporary storage. Data loaded into RAM, from the hard-drive or ROM, will be lost when the computer is powered down. Remember to save what is in RAM to hard-drive before you power off or you will lose whatever you did. RAM is where you work on things. The larger the desktop, the more different things you can see and be working on at once, without having to put something away or covering it up with something else.