Trackball

A trackball is a pointing device consisting of a ball housed in a socket containing sensors to detect rotation of the ball about two axes—like an upside-down mouse, but with the ball sticking out more. The user rolls the ball with their thumb, fingers, or the palm of their hand to move a cursor. Tracker balls are common on CAD workstations for ease of use and, before the advent of the touchpad, on portable computers, where there may be no desk space on which to use a mouse. Some clip onto the side of the keyboard and have integral buttons which have the same function as mouse buttons. Trackballs are sometimes seen on computerised special-purpose workstations, such as the radar consoles in an air-traffic control room or sonar equipment on a ship or submarine. Modern installations of such equipment may use mice instead, since most people now already know how to use one. However, military mobile anti-aircraft radars and submarine sonars tend to continue using trackballs, since they can be made much more durable and are more fit for fast emergency use.
Trackballs have had some limited use in computer and video games, particularly early arcade games (see a List of trackball arcade games). One of the more famous games to use one is Centipede. "Football", by Atari, was the first game to use a trackball, released in 1978 for the arcade. Console trackballs, meanwhile, are fairly uncommon. The Bandai Atmark, a Japanese console, had a trackball as standard for its gamepad, and the Atari 2600 had one as a peripheral, with a joystick as standard. As of today, trackballs are often in use in pub golf machines (such as Golden Tee) to simulate swinging the club. Trackballs are provided as the pointing device in some public internet access terminals. Unlike a mouse, a trackball can easily be built into the console - and, as such, cannot be ripped away or otherwise vandalised. Two examples are the Internet browsing consoles provided in some UK McDonalds outlets, and the BT Broadband Internet public phone boxes.