Microsoft IntelliMouse Optical 4.0 is the solution. Microsoft have replaced the old-fashioned mouse ball with an IntelliEye optical sensor that tracks movement 1, 500 times per second - providing smooth and precise motion. No mouse ball means no moving parts to clean or wear down. And, the optical sensor is sealed in to keep out the dirt and lint that can cause a traditional mouse to skip or jam. Browse the Web without using toolbars or the keyboard. Simply use either side button to go forward or backward on the Internet. Or you can program the buttons to execute routine actions in many of your favorite programs.