If you go to a picnic, you later have memories of it. You may remember the taste of the food, the excitement of the games, and the names of friends who were there. With the passage of time, however, you will probably forget some of the details.
A computer’s memory is different. No matter how you program it, the computer cannot remember such things as the taste of food or the feeling of excitement. But it can remember names. Your computer will easily keep track of the names of everyone who attended the picnic.
Of course, the computer doesn’t already know the names. You have to tell it the names of the picnickers. Once you supply it with that input, the computer’s memory, unlike yours, will never forget. The list will always be complete and always correct—as long as the computer is turned on. When you turn it off, the list disappears. Why does this happen?
The computer has two kinds of memory. One kind is called read-only memory, or ROM, and it is not affected when you turn off the machine. ROM is permanent memory. The second kind of memory is called random- access memory, or RAM, and this is the kind of memory in which your list of picnickers was stored. RAM is temporary memory.