Touchpad

A touchpad (also known as a "trackpad") is an input device commonly used in laptop computers. They are used to move the cursor, using motions of the user's finger. They substitute for a computer mouse. Touchpads vary in size but are rarely made larger than 50 cm² (about 8 in²)

Touchpads commonly operate by sensing the capacitance of a finger. Capacitive sensors are laid out along the horizontal and vertical axis of the touchpad. The location of the finger is determined from the pattern of capacitance from these sensors.

Touchpads are relative motion devices. That is, there is no isomorphism from the screen to the touchpad. Instead, relative motion of the user's fingers causes relative motion of the cursor. The two buttons below or above the pad serves as mouse standard buttons. You can also click by tapping your finger on the touchpad, and drag with a tap following by a continuous pointing motion (a click-and-a-half).

Some touch pads also have "hotspots": locations on the touchpad that indicate user intentions other than pointing. For example, on certain touchpads, moving your finger along the right edge of the touch pad will control the scrollbar and scroll the window that has the focus.

Touchpads are primarily used in portable laptop computers, because the usual mouse device requires a flat table adjacent to the keyboard not always available away from the office. But touchpads have some advantages over the mouse, particularly that the pad's position is fixed relative to the keyboard, and very short finger movements are required to move the cursor across the display screen. Some computer users prefer them for such reasons, and desktop keyboards with built-in touchpads are available from specialist manufacturers.

Major manufacturers of touchpads include Synaptics, Alps Electric Corporation, and Cirque Corporation.

See also: pointing device, pointing stick.