"Oh, just do what I want, you confounded machine!"
To communicate with computers, we need go-betweens. At a basic level, we need something to relay information from the computer to us, and from us to the computer. We call these translation aids input devices, output devices, and controls.
Input devices are the hardware components you use to "talk" to a computer. You use them to place requests, send messages (to the computer or to other people), move around in virtual worlds, or even shoot at "enemies" in some computer games. The following objects are commonly used input devices are:
Each input device is optimized for certain uses or users and is less efficient or less convenient for others. For example, a microphone used with voice-recognition software can be very helpful for people who can't use a keyboard (because of their work environment or disability). But voice input is difficult in very noisy places, impractical in situations where quiet is required, and possibly more error-prone than some other techniques. Joysticks and trackballs are well-suited for navigational control, as in video games or exploration of three-dimensional environments, where smooth movement is more important than fine target acquisition. Pen input can be very convenient for a package carrier recording delivery signatures, but learning to use pen gestures as commands requires some study and practice. No one input device is best for every situation.
Output devices are the various hardware elements a computer uses to communicate with the user. The following objects are examples of output devices:
Like input devices, these devices are specialized for particular uses. The head-mounted displays and headphones, for example, are used for immersive virtual reality applications, such as arcade games and flight simulators. They present three-dimensional images to the user's eyes and stereo sound to the ears, while excluding the sights and sounds of the user's physical environment. The illusion of being in another world can be very compelling. But using such a device for extended periods of time, as when performing office tasks, could cause problems. The user can suffer nausea from the disparity between the motion perceived by the inner ear and that perceived by the eyes; eyestrain from extended near focus on the display; neckstrain from the weight of the helmet; and discomfort from heat buildup in the helmet and headphones. The user is also socially isolated from peers (a mixed blessing). Refinements to the technology will ease some of these problems, while others are intrinsic to each medium.
Controls are the software elements, usually shown on a display, that you use to set preferences and make choices. Like such hardware controls as knobs and dials, they can be used to control many different things. Some familiar controls include the following objects:
Some software controls are used for both output and input; they show your choices or the current setting, and they help you to operate the control.
These elements are all necessary for interaction between people and computers, but they are not enough to guarantee a "meeting of the minds." We also need an interface that is easy to understand and to use.