When a program is loaded into memory, the instructions composing it are lined up in RAM, ready to be executed. When a computer is turned off, its RAM is wiped clean. That's the reason why it takes a few seconds for a program to load when you click on its icon. People marvel at the mind-boggling graphics of which current PC's are capable. In reality, there is nothing magical about the phosphorescent images in video games, Web pages, and multimedia.
Programs manipulate pictures on the screen by shuttling numbers into and out of video memory.
From the perspective of the lightening-fast CPU, disk accesses take a lot of time. The more RAM a computer has, the fewer disk accesses will be required, and the faster the computer will run. One of the things that they do differ on is operating systems. IBM operating systems include DOS, Windows 3.1, and Windows 95. Think of the operating system as a waiter at a pizzeria.