The whole mouse is a super sensitive button. Trackball cursor controls operate much like an inverted mouse. Instead of moving the mouse with your hand, the trackball allows you to move the cursor by rotating a ball with your fingers. With desktop computers, trackballs are fairly large for easier maneuvering and come sitting inside some kind of a holder. Trackballs are hardly ever found on current notebook computers.
Most notebook computers use integrated touchpads or pointers.
The base of a trackball device doesn't move so there is less strain on your wrists and hands, and less desk space that needs to be used to control the pointer. Touchpads are more often found on notebook computers than as external devices with desktop computers. Touchpads also come with buttons for maneuvering. Most standard mice for PC desktop computers come with a left button and a right button. Macintosh computer mice usually have just one main button.