The processor or CPU (central processing unit) is the main chip in a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions. Basically, this is the brain of the computer and the faster it is the better. They come in many speeds and some computers have more then one. They also come with multiple cores to make it easier to run multiple tasks at once. Make sure the one you get is compatible with your motherboard.