TRACKBALL

A Trackball is a pointing  device that works like a mouse. Trackball contains a ball exposed on its surface. To move the pointer on the screen, you roll the ball with your thumb, fingers, or the palm of your  hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons.The advantage of  trackball over mouse is that the trackball is stationary so it dose note require much space for use. In  additions, you can place a trackball on any type of surface. For both these reasons, trackball are popular pointing devices for portable computer.