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.
Major manufacturers of touchpads include Synaptics, Alps Electric Corporation, and Cirque Corporation.
See also: pointing device, pointing stick.