The central processing unit is at the center of your computer. It's often referred to as the brain of the PC, but in some ways it functions more like the heart and lungs, drawing instructions into it and sending out a result. A program is made up of a series of instructions. The CPU processes these instructions one at a time, first fetching the instruction, then decoding it, then executing it and finally returning and storing a result. The CPU cycles through these functions with every instruction in a program.