Mouse

Mouse

In 1963 Douglas C. Engelbart (1925–), working at the Stanford Research Institute, was investigating different ways for humans to communicate with computers. He thought that a pointing device, something that a computer user could move by hand causing a corresponding movement in an object on the screen, would be easier to use and more intuitive than the existing keyboard. The computer mouse made its debut in 1968 at a computer conference in San Francisco, but it was not widely used until the introduction of personal computers in the 1980s. Since then, it has become a very popular pointing device for operating environments that provide graphical user interfaces (GUIs) .

The mouse is used in conjunction with the keyboard to perform tasks such as moving and pointing to objects displayed on the screen, selecting commands from menus, and working with drawing and painting programs. A mouse ﾀ has one, two, or three buttons that can be pressed to send to the computer signals that activate commands. As the mouse is moved around a desktop, the on-screen pointer mimics its motion. This technique provides an extremely fast and smooth way to navigate around the computer screen.

How does a computer mouse work? There are two distinct user movements that activate the mouse: moving it around a desktop, and pressing one of its buttons.

As the mouse moves around a desktop, the tracking ball—a rubber ball underneath its body—translates the mouse movements into input signals that the computer can understand. Those signals are carried to the computer by the long cable that connects the mouse to one of the computer's ports. As the ball spins, it makes contact with and rotates two rollers installed at a 90-degree angle to each other. One of the rollers reacts to back-and-forth movements of the mouse, which translate into up-and-down movements of the on-screen pointer. The other roller detects sideways movements, which translate into side-to-side movements for the on-screen pointer. Each roller is joined to a wheel, called an encoder, which has a set of tiny metal bars, called contact points, on its rim. When the rollers go around, the encoders do the same, and their contact points touch two pairs of contact bars that reach out from the mouse's cover, thus generating an electrical signal.

A new signal is sent every time a connection is made between the contact points and the contact bars. The total number of signals shows how far the mouse has moved: a large number of signals means it has moved a long distance. The direction in which the mouse is moving—up-and-down or sideways—is communicated by the direction in which the rollers are turning and the ratio between the number of signals from each of the rollers.

The signals sent to the computer through the mouse's tail are used by the software that empowers the mouse. This software converts the number of signals from the encoders and rollers to determine how far and in which direction the on-screen pointer will move. The frequency of signals indicates the speed needed to move the on-screen pointer.

Each of the buttons on the top of the mouse covers a tiny switch that records when a button is pressed or clicked, and the time interval between clicks. Pressing one of the buttons on the mouse sends a signal to the computer, which again is passed on to the software. Based on how many times a user clicks the button, and where the on-screen pointer is positioned during these clicks, the software will execute the task selected.

Mouse Variations

A trackball is an upside-down mouse. With a trackball, the user spins a ball with his or her fingers to determine the speed and direction of the on-screen pointer. This is useful with laptop or notebook computers and other portable computers where there may be no desktop available.

A wireless mouse, a mouse without a cord, can also be used to perform pointing and clicking actions. Wireless mice use infrared or radio signals to communicate with the computer.

see also Game Controllers; Hypertext; Interactive Systems; Microcomputers; Pointing Devices.

Ida M. Flynn

Bibliography

"Input/Output." Understanding Computers. Alexandria, VA: Time-Life Books, 1986.

White, Ron. How Computers Work, 2nd ed. Emeryville, CA: Ziff-Davis Press, 1997.

ﾀ The computer mouse gets its name from its resemblance to a real mouse: it has a small body and long tail.