Have you ever opened a basic mouse? The basic mouse has a ball inside. This ball touches the table desktop and rolls when you move a mouse. The movement of your hand is transferred to the mouse. This ball is not present in an optical mouse. The optical mouse has red light-emitting diode. This small red light reflects from the surface on which it is moved. The light falls on complimentary metal-oxide semiconductor sensor (CMOS) and each image of dragging movement is sent to digital signal processor. Hundreds of such images are sent to the computer each second and hence the cursor movement is smooth over the computer screen.

The basic mouse has two rollers that touch the ball and detect the movement in X and Y directions. These directions refer to the co-ordinate geometrical directions. The optical mouse can be kept dirt free and thus tracking is smooth. They do not require mouse-pads or other special surface.