Touchpad

A touchpad or trackpad is a type of pointing device. Its largest component is a tactile sensor: an electronic device with a flat surface that detects the position and motion of a user's fingers, and translates them into 2D motion to control a pointer in a graphical user interface. Touchpads are common on laptop computers, contrasted with desktop computers, with which mice are more prevalent. Trackpads are sometimes used with desktop setups where desk space is scarce. Wireless touchpads are also available as detached accessories. Due to the ability of trackpads to be made small, they were additionally used on personal digital assistants (PDAs) and some portable media players.

Touchpads operate in several ways, including capacitive sensing or resistive touchscreen. The most common technology used in the 2010s senses the change of capacitance where a finger touches the pad. Capacitance-based touchpads will not sense the tip of a pencil or other similar ungrounded or non-conducting implements. Fingers insulated by a glove may also be problematic, and capacitive touchpads are rarely used as pointing devices for medical hardware.

Like touchscreens, touchpads sense absolute position but their resolution is limited by their size. For common use as a pointer device, the dragging motion of a finger is translated into a finer, relative motion of the cursor on the output to the display on the operating system, analogous to the handling of a mouse that is lifted and put back on a surface. Hardware buttons equivalent to a standard mouse's left and right buttons are sometimes positioned adjacent to the touchpad.

Some touchpads and associated device driver software may interpret tapping the pad as a mouse click, and a tap followed by a continuous pointing motion (a "click-and-a-half") can indicate dragging. Tactile touchpads allow for clicking and dragging by incorporating button functionality into the surface of the touchpad itself. To select, one presses down on the touchpad instead of a physical button. To drag, instead of performing the "click-and-a-half" technique, the user presses down while on the object, drags without releasing pressure, and lets go when done. Touchpad drivers can also allow the use of multiple fingers to emulate the other mouse buttons (commonly two-finger tapping for right click).

Touchpads are called clickpads if they rely on software buttons rather than physical buttons. Physically the whole clickpad formed a button, logically the driver interprets a click as a left or right button click depending on the placement of fingers.

Some touchpads have "hotspots", locations on the touchpad used for functionality beyond a mouse. For example, on certain touchpads, moving the finger along an edge of the touch pad will act as a scroll wheel, controlling the scrollbar and scrolling the window that has the focus, vertically or horizontally. Many touchpads use two-finger dragging for scrolling. Also, some touchpad drivers support tap zones, regions where a tap will execute a function, for example, pausing a media player or launching an application. All of these functions are implemented in the touchpad device driver software, and can be disabled.

In 1980, Xerox offered one of the first, if not the first, touchpads on a computer system with their Xerox 860, a word processing workstation aimed at medium- and large-sized businesses. Embedded on the Xerox 860's keyboard, to the right of the keys, is the circular touchpad, which Xerox dubbed the "Cat" (short for capacitance-activated transducer). Xerox offered the Cat as an alternative input method for selecting strings of text to copy, delete, insert, or move around the document.

By 1982, Apollo desktop computers were equipped with a touchpad on the right side of the keyboard. Introduced a year later, in 1983, the first battery-powered clamshell laptop, the Gavilan SC included a touchpad, which was mounted above its keyboard, rather than below, which became the norm.