Why pointing needed devices
To work with a picture on a screen, a person needs a way to say “this one” or “here”. Typed coordinates are slow, and keyboard cursor keys step one position at a time. Several kinds of device were developed to let a hand indicate a position directly. They differ in how they sense movement, where the user holds them and what kinds of work they suit. The mouse was one answer, and an effective one, but it joined a field that already had other entries.
The light pen
A light pen is a pen-shaped device with a light-sensing tip. It is touched to a display, and the computer works out the position from the moment the screen’s beam passes the pen. Light pens were used with early display systems in the 1950s. They were part of the SAGE air defense system, where operators used a light gun to select targets on a radar-style screen. Ivan Sutherland’s Sketchpad in 1963 used a light pen for drawing, and it was an influential demonstration of interactive graphics.
The strengths of the light pen were directness and intuition: the user pointed at the object itself. The weaknesses were physical. Holding an arm up against a vertical screen is tiring, and the pen works only with certain kinds of display. When screens changed to flat panels, light pens faded, although the idea returned in stylus-based touchscreens.
The trackball
A trackball is a ball, mounted in a base, that is rolled by the fingers or palm to move a cursor. An early example was built for the Canadian navy’s DATAR system, a project of the early 1950s. Trackballs were later used in air traffic control, in arcade games such as Missile Command and in some laptops.
A trackball stays in one place, which is useful where space is tight or where a machine is operated while mounted. The ball is easy to control precisely with practice. It can be less comfortable for long periods of rapid movement than a mouse, though some users prefer it for reasons of wrist comfort.
The joystick
A joystick is a lever that tilts in two directions. It was adapted from aircraft controls and came into computers in the form of control sticks for simulation and games. A joystick reports the direction and amount of tilt, which suits steering and speed control, less well than placing a cursor at an exact spot. Joysticks became common in home computing and gaming, and found uses in control of equipment and wheelchairs.
Graphics tablets
A graphics tablet is a flat surface paired with a pen or puck. The user draws or points on the tablet, and the position is sent to the computer. Unlike a mouse, a tablet is absolute: each point on the tablet corresponds to a specific point on the screen. The RAND Tablet, developed by the RAND Corporation in the mid-1960s, was an early example. Tablets suit drawing, tracing maps and design work, and modern pen tablets are still used by illustrators and designers.
Where the mouse differs
A mouse is a relative device. It reports movement, not position, so the user can lift and reposition it on a desk without moving the cursor. This is helpful because a small desk area can cover a large screen, and the user can adjust arm position for comfort. The mouse also stays on the desk, so the arm rests, and the screen can sit upright.
Early tests by Engelbart’s group, with William English, compared the mouse with other devices for selecting objects on a screen, and the mouse performed well in speed and error rate for their tasks. A later study, with different participants and conditions, would not necessarily show identical results, which is a reason to treat any single comparison cautiously.
Pointing in portable and touch devices
When computers became portable, new devices appeared, including pointing sticks and touchpads, and they borrowed ideas from the older ones. Touchscreen interfaces returned to the idea of pointing directly at the display, like the light pen but with a finger. Voice, eye tracking and gesture control have been tried as alternatives for people who cannot use a hand, and they remain areas of development.
Why variety persists
No single device is best for every task. Artists prefer pens and tablets, gamers often favor mice, and engineers might choose a trackball in a cramped space. Looking at the history, the mouse succeeded because it was cheap, reliable, comfortable and well supported by software, in addition to being a good design. Technical merit alone rarely decides which input device wins.