Page 115 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 6: Hardware

6.4 input Devices notes

Often, input devices are under direct control by a human user, who uses them to communicate
commands or other information to be processed by the computer, which may then transmit
feedback to the user through an output device. Input and output devices together make up the
hardware interface between a computer and the user or external world. Typical examples of
input devices include keyboards and mice. However, there are others which provide many more
degrees of freedom. In general, any sensor which monitors, scans for and accepts information
from the external world can be considered an input device, whether or not the information is
under the direct control of a user.

6.4.1 Classification of Input Devices
Input devices can be classified according to:
• The modality of input (e.g., mechanical motion, audio, visual, sound, etc.)
• Whether the input is discrete (e.g., keypresses) or continuous (e.g., a mouse’s position,
though digitized into a discrete quantity, is high-resolution enough to be thought of as
continuous).

• The number of degrees of freedom involved (e.g. many mice allow 2D positional input,
but some devices allow 3D input, such as the Logitech Magellan Space Mouse) Pointing
devices, which are input devices used to specify a position in space.
• Whether the input is direct or indirect. With direct input, the input space coincides with
the display space, i.e. pointing is done in the space where visual feedback or the cursor
appears. Touchscreens and light pens involve direct input. Examples involving indirect
input include the mouse and trackball.

• Whether the positional information is absolute (e.g., on a touchscreen) or relative (e.g., with
a mouse that can be lifted and repositioned).
Note that 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 setup to simulate a relative input mode where the stylus or puck can be lifted and
repositioned.
Keyboards
A keyboard is the most common method of interaction with a computer. Keyboards provide
various tactile responses (from firm to mushy) and have various layouts depending upon your
computer system and keyboard model. Keyboards are typically rated for at least 50 million cycles
(the number of times a key can be pressed before it might suffer breakdown).
The most common keyboard for PCs is the 101 style (which provides 101 keys), although many
styles are available with more or fewer special keys, LEDs, and others features, such as a plastic
membrane cover for industrial or food-service applications or flexible “ergonomic” styles.
Macintosh keyboards connect to the Apple Desktop Bus (ADB), which manages all forms of user
input from digitizing tablets to mice.
Example of types of keyboards:

• Computer keyboard
• Keyer
• Chorded keyboard
• LPFK

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