Input device

In computing, an input device is a piece of equipment used to provide data and control signals to an information processing system, such as a computer or information appliance. Examples of input devices include keyboards, computer mice, scanners, cameras, joysticks, and microphones.
Input devices can be categorized based on:
A keyboard is a human interface device which is represented as a matrix of buttons. Each button, or key, can be used to either input an alphanumeric character to a computer, or to call upon a particular function of the computer. It acts as the main text entry interface for most users.
Keyboards are available in many form factors, depending on the use case. Standard keyboards can be categorized by its size and number of keys, and the type of switch it employs. Other keyboards cater to specific use cases, such as a numeric keypad or a keyer.
Desktop keyboards are typically large, often have full key travel distance, and features such as multimedia keys and a numeric keypad. Keyboards on laptops and tablets typically compromise on comfort to achieve a thin figure.
There are various switch technologies used in modern keyboards, such as mechanical switches (which use springs), scissor switches (usually found on a laptop keyboard), or a membrane.
Other keyboards do not have physical keys, such as a virtual keyboard, or a projection keyboard.
A pointing device allows a user to input spatial data to a computer. It is commonly used as a simple and intuitive way to select items on a computer screen on a graphical user interface (GUI), either by moving a mouse pointer, or, in the case of a touch screen, by physically touching the item on screen. Common pointing devices include mice, touchpads, and touch screens.
Whereas mice operate by detecting their displacement on a surface, analog devices, such as 3D mice, joysticks, or pointing sticks, function by reporting their angle of deflection.
Pointing devices can be classified on:
Direct input is almost necessarily absolute, but indirect input may be either absolute or relative. For example, digitizing graphics tablets that do not have an embedded screen involve indirect input and sense absolute positions and are often run in an absolute input mode, but they may also be set up to simulate a relative input mode like that of a touchpad, where the stylus or puck can be lifted and repositioned. Embedded LCD tablets, which are also referred to as graphics tablet monitors, are the extension of digitizing graphics tablets. They enable users to see the real-time positions via the screen while being used.
A sensor is an input device which produces data based on physical properties.
Sensors are commonly found in mobile devices to detect their physical orientation and acceleration, but may also be found in desktop computers in the form of a thermometer used to monitor system temperature.
Some sensors can be built with MEMS, which allows them to be microscopic in size.
Some devices allow many continuous degrees of freedom as input. These can be used as pointing devices, but are generally used in ways that don't involve pointing to a location in space, such as the control of a camera angle while in 3D applications. These kinds of devices are typically used in virtual reality systems (CAVEs), where input that registers six degrees of freedom is required.
Input devices, such as buttons and joysticks, can be combined on a single physical device that could be thought of as a composite device. Many gaming devices have controllers like this. Technically mice are composite devices, as they both track movement and provide buttons for clicking, but composite devices are generally considered to have more than two different forms of input.
Video input devices are used to digitize images or video from the outside world into the computer. The information can be stored in a multitude of formats depending on the user's requirement.
Many video input devices use a camera sensor.
Voice input devices are used to capture sound. In some cases, an audio output device can be used as an input device, in order to capture produced sound. Audio input devices allow a user to send audio info to a computer for processing, recording, or carrying out commands. Devices such as microphones allow users to speak to the computer in order to record a voice message or navigate software. Aside from recording, audio input devices are also used with speech recognition software.
Punched cards and punched tapes were used often in the 20th century. A punched hole represented a one; its absence represented a zero. A mechanical or optical reader was used to input a punched card or tape.