When you turn on your computer, the main memory (RAM) is completely empty. The first thing the computer needs to do is to transfer the operating system from the hard disk to the main memory.

After the operating system is loaded to main memory, you can execute (run) any program (application software) you like. This is usually done by clicking, double clicking, or tapping the program’s corresponding icon. For example, let’s say you click on the icon of your favorite word processor. This action orders your computer to load (or copy) the word processing program from your hard disk to the main memory so the CPU can execute it.

Remember! Programs are stored on secondary storage devices such as hard disks. When you install a program on your computer, the program is actually copied to your hard disk. But when you execute a program, the program is copied (loaded) from your hard disk to the main memory, and that copy of the program is executed.

Notice: The terms “run” and “execute” are synonymous.