A mouse is a handheld pointing device for personal computers, involving a small object shaped to sit naturally under the palm, fitted with several buttons, and an electrical cord to interface back with the computer. On the underside of the mouse, there is a ball which rolls as the mouse is moved along a flat surface by the users, which converts its movement within a certain area into movements of a cursor on the display. Wireless variants exist, using either infra-red or radio, as well as optical mice which do not use a mouse ball but use other techniques to detect the mouse's movement.
The standard PC mouse has two buttons, but many have three buttons. In the past five years, a scroll wheel - a special button that as well as being able to be pressed can be rotated and thus adding a third degree of movement to the mouse - has become common. Mice with more than one button will have different functions assigned to each one by the application or operating system. For instance, a computer configured in the standard way will use the left button in a web browser to follow links, while the right button brings up a context-sensitive menu allowing the user to copy graphics or a link location, go back in the browser's history, and so forth, unless ECMAScript code on a particular page attempts to enforce weak security by disabling the right-click button (this practice heavily annoys most users, and none of the 100 most popular web sites do this). Apple continue to release mice with only one button, as their studies show single-button mice to be more efficient to use. (To simulate a "right click", users hold the control key while clicking.) XFree86 is designed for a three button mouse but will optionally simulate a middle-click when the left and right mouse buttons are clicked at the same time.
The mouse was invented by Douglas Engelbart of Stanford Research Center in 1963 after extensive usability testing, based on an earlier stationary device called a trackball that contained a large ball that the user's hand rotated. The first mice were basically inverted trackballs, where the user moving the device caused the ball underneath to move by friction against the table or a special pad. Later mice used optical or inertial mechanisms to detect movement.
Units of mouse movements are calculated in mickies.