A small peripheral device that controls the movement of the pointer on a display screen; also called "mouse cursor", "mouse pointer", "e-rodent". By rolling the mouse along a flat horizontal surface (to improve traction a small piece of textured material, called a "mouse pad", is often used), a pointer correspondently moves on the display screen. All mice have at least one activation button, and may have as many as three, with a scroll wheel for reviewing long documents; the function of the mouse button varies from system to application. Invented by Douglas C. Engelbart / Englehart of Stanford Research Center in 1963, and pioneered by Xerox in the 1970s, the mouse is an ergonomic alternative to keyboarding commands. It is possible to "mouse ahead" with moves so swift that the computer's response will be delayed. In graphical user interfaces (GUI), the mouse cursor can point to options or objects and activate them by clicking a mouse button. Such "clickable" environments, known as "point-and-click", include symbols that change shape depending upon context, or change options depending upon application. System functions, like "drag-and-drop", are program independent. In graphics programs, the mouse may be used as a pen, stylus, or paintbrush to illustrate objects. There are several types of mice: (1) mechanical: has a rubber or metal ball on its underside that can roll in all directions, so the mechanical sensors (called "encoders") within the mouse will detect the direction the ball is rolling and move the screen pointer accordingly; (2) optomechanical: similar to a mechanical mouse, but uses optical sensors to detect the motion of the ball; (3) optical: uses a laser (no mechanical moving parts) to detect the mouse's movement, which is moved along a special grid mat, so that the optical mechanism has a frame of reference for rapid response. A flying mouse can be lifted off the desk, and used as a three-dimensional pointer. A mouse may be foot-operated for special circumstances. Mice connect to computers variously by: specific socket ("mouse port"), RS-232C or PS/2 serial port ("serial mouse"), expansion board ("bus mouse"), ADB port ("Macintosh mouse"). Cordless mice aren't physically connected, but rely upon infrared or radio waves to communicate with the computer. The term commonly derives from its resemblance to a long-tailed rodent scurrying across a desktop; but the word means "small". See pointer, trackball, joystick, insertion point.