Reference Series Table of Contents For This Issue

How Computers Work, Part I
August 2001• Vol.5 Issue 3
Page(s) 90-95 in print issue

Dissecting Mice & Trackballs To Define Their Mass Appeal
Discover How These Input Devices Help Us Maximize Computing Efficiency
Point and click. Drag and drop. Double-click. These words are part of our everyday computing vocabulary, thanks to the computer mouse that sits next to nearly all PCs used today. For instance, tell a user to double-click the Recycle Bin on their Desktop, and chances are they’ll know exactly to what you’re referring.

Like these familiar phrases, we’ve become so accustomed to using a mouse that we rarely give it a second thought. We simply cup the palm-sized peripheral in our hand, glide it smoothly around a mousepad, and click repeatedly throughout the day, opening menus and documents, highlighting and moving text, scrolling through documents, resizing windows, and pulling up menus of shortcuts and commands.

Despite the lack of attention we give the mouse, it’s nearly impossible to imagine accomplishing anything quickly and efficiently without it. Used in tandem with a GUI (graphical user interface) such as Windows, mice are imperative to carrying out our daily tasks. Imagine trying to quickly navigate Web pages or open e-mail messages without a mouse.

The efficiency and speed mice provide has been duplicated in other input devices, such as touch screens, touchpads, pointing sticks, digitized tablets, light pens, voice recognition software, and probably the most popular mouse alternative—trackballs. (Trackballs, by the way, are basically just mice turned upside down.) When we stop to recognize the functionality, ease of use, and speed that input devices provide, it’s easy to understand why they are such integral computing tools.

For most of us, operating an input device, such as the mouse, is simply a matter of maneuvering it in the direction we want our pointer to move on the monitor screen. But underneath its plastic case, a series of interconnected moving parts set actions into motion. Throughout this article, we’ll detail how these parts work together to operate a basic mouse. Also, we’ll look at how the mouse was developed, how it has evolved, and what its future holds.

  Mice Species. On the exterior, mice vary in the number of buttons they have and how they interface with a computer. But in general, manufacturers design most mice with ergonomic comfort in mind. Typically, mice are palm-sized with a rounded, sloped body that fits the natural curve of the hand. Also, manufacturers sculpt some mice along the sides for a better grip and texture them to provide more traction.

Below the surface, there are basically three types of mice: mechanical, optomechanical, and optical.

Mechanical and optomechanical mice have a rubber ball housed inside the casing, which protrudes slightly from underneath the mouse. Inside the mouse, the ball sits between two rollers, perpendicular to one another. A third, spring-loaded roller holds the ball in place. The rollers each connect to a shaft with a wheel (thin disk) connected at the other end. When the mouse is set in motion, the ball moves, rotating the rollers, and concurrently spinning the wheels.

In mechanical mice, the movement of the wheels causes sensors to send electrical signals through the mouse cord to the computer, where software interprets the signals into mouse movements. In optomechanical mice, it’s the LED (light-emitting diodes) that sense mouse movements. We’ll take an in-depth look at how optomechanical mice work later.

Optical mice have no moving parts. Instead, LEDs in the mouse work with a special reflective mousepad consisting of gridlines. The LEDs generate two different colors of light. The mousepad’s horizontal gridlines contain one color and the vertical gridlines consist of the other. As the mouse moves over the mousepad, the LEDs and light detectors determine when colors of light move over gridlines of the same color. This information transmits to the computer where the software interprets it as mouse movements.

Unlike mechanical mice that users must clean periodically to rid of dirt and grime that collect inside the casing, optical mice don’t need cleaning because they have no openings or moving parts. However, optical mice are generally more expensive and require a dedicated mousepad. Despite their ability to track mouse movements faster, optical mice have yet to find a mass audience.

  Inside An Optomechanical Mouse. Optomechanical mice are the most commonly used mice for desktop computers. The name refers to the combination of optical and mechanical parts that translate data into mouse movements. If you take an optomechanical mouse apart, you’d find a fairly simple, yet effective, design inside.

The operation of an optomechanical mouse relies on the movement of a rubber-coated ball that sits between the two perpendicular rollers inside the mouse. One roller controls up and down cursor movements, or movements on the Y axis. The other roller controls side-to-side movements, or movements on the X axis. A third, spring-loaded roller keeps the ball pressed tightly against the other rollers.

Each roller connects to a thin axle, which has a larger wheel attached to the other end. Each wheel has many tiny slits cut out around the rim and sits directly between a LED and a sensor, which connect to a circuit board. The LED emits a constant light that the sensor receives. When the mouse moves, the parts work together to cause a series of actions.

First, the movement of the rubber ball spins the rollers, which in turn causes the wheels to rotate. As the wheels rotate, the light from the LED either passes through the tiny slits on the wheel to the sensor or the solid portions of the wheel block it. The light sensor senses these changes in the light pattern. The data is sent to the computer through the mouse cord, or “tail,” where the mouse driver tallies the number of changes in light and how often they occur to calculate the direction, pace, and distance the mouse is moving. (A mouse driver is a special program that allows the computer and mouse to communicate).

A typical optomechanical mouse also includes two mouse buttons, which are vital to using the mouse with a GUI. These buttons are referred to as the left-mouse button and the right-mouse button. Users click the left button to select menu items, start programs, activate icons, highlight and move text, resize windows, maximize and minimize windows, and other functions. Users typically click the right button to activate shortcut menus or commands in an application.

Inside the mouse, there’s a small switch for each button connected to a circuit board. When users click a button, it presses on top of the switch and creates a signal that passes through the mouse cord to the computer. There, the computer and software interpret the signal and execute the appropriate action.

A trackball is much like an optomechanical mouse. If you turn a mouse on its back, you have the basic idea of a trackball, except that the rubber-coated ball that a mouse uses is replaced with a smooth, golf-ball-sized ball protruding from the top of the body. Like a mouse, when the ball spins, it causes two rollers touching the ball to rotate and send data to the computer. Unlike a mouse, a trackball is stationary. Users spin the ball in its cradle using fingers or a thumb. Trackballs requires less desktop space but more coordination to use.

  Mice Varieties. The majority of mice have two buttons, but many models have three, four, or five buttons that add more functionality. (Apple Computer’s mice have only one button.) Newer models also have a scroll button to help users move Web pages and documents up and down without using a scroll bar. The button (or wheel) usually sits between the left and right buttons, and a finger controls its actions. Most scroll buttons can zoom in and out of compatible applications and act as a third button.

Windows includes a standard mouse driver that allows most mice to work immediately after installation. But to take advantage of extra buttons and a scroll wheel, users must install special software (such as Microsoft’s IntelliPoint, Kensington’s MouseWorks, and Logitech’s MouseWare software).

The added functionality that extra buttons provide includes the ability to program buttons to open and close applications, display Help windows, toggle between applications, open files and programs with one click, and display menus of frequently used applications. Users can also program buttons to navigate Web pages, scroll in multiple directions, scroll without using a scroll wheel or scroll bars, and other functions.

In addition, mice vary in how they interface with the computer. Most mice use a cord that extends from the mouse’s body to the back of the computer and inserts into a port. However, cordless mice have become more popular in recent years because they work away from the desktop and eliminate the inconvenience of a mouse cord.

A cordless mouse uses a small receiver that inserts into a serial or PS/2 port. (PS/2 ports are the de facto standard for all mouse and keyboard ports on IBM-compatible computers. The 6-pin port was originally developed by IBM for its PS/2 line of computers, but was eventually adapted by other computer manufacturers.) The mouse receives power from two AA alkaline batteries and sends either infrared or radio signals to the receiver, which transmits data to the computer. Generally, the mouse can communicate with the receiver at distances of about six to eight feet away.

Infrared and radio technology models differ in that infrared models need a clear, unobstructed path to the receiver. The receiver needs to be in a clear, open location, and the mouse needs to be directly in line with the receiver. Radio technology models, such as Logitech’s Cordless MouseMan and Wheel Mouse models, don’t need a clear pathway. The receiver can be placed anywhere on the desktop (without a direct line to the mouse) and still receive signals.

  Making Connections. Until a few years ago, most mice and trackballs used a serial port to connect to a computer. Nearly all mice now use a PS/2 port (developed by IBM) to connect, although users can still utilize a serial port if they wish. Also, more models are beginning to use a USB (Univer sal Serial Bus) connection.

Most computers have two serial ports, each of which look like trapezoids with nine pins protruding from them. Many computers also have two PS/2 ports, one for the mouse and one for the keyboard. The PS/2 port looks like a small circle and has six holes that the mouse connector inserts into. A USB port looks like a small square opening.

Several mouse manufacturers bundle their models with a serial-to-PS/2 or PS/2-to-serial adapter to give you the option of connecting the mouse to either port. Adapters are cheap and available at computer stores. PS/2 ports became popular because they allow users to reserve their serial ports for peripherals other than the mouse.

No matter what connection it uses, the mouse is an invaluable tool to daily computing chores. Understanding how its parts work together will help you appreciate just how important this little marvel really is. Now, for another perspective, let’s analyze how mice became a part of our computing lives in the first place.

  History & Status. The next time you’re sitting at your computer, take a long look at the mouse sitting next to it. Try to imagine if it was gone and you had to carry out your daily computing tasks without it. Not a pleasant thought, is it?

It wasn’t that long ago when users performed their computing chores without the convenience and speed that a mouse provides. Mice didn’t really become popular with home users until the mid-1980s with the introduction of Apple Computer’s first Macintosh computer. Then the mouse’s popularity soared when GUIs became widespread. The combination of a mouse and GUI, such as Windows, gave users point-and-click simplicity, replacing the need to type in lines of code to execute commands.

As mouse sales exploded, mouse designs and applications progressed, as well. Even so, the technology used to operate a mouse has changed very little since its invention by Douglas Engelbart in 1963. But that stance is changing; some pundits predict that changes to input devices will become so dramatic in upcoming years that mice might become extinct. However, the experts we spoke with say that prognosis is a bit premature.

In this section of the article, we’ll detail how the mouse evolved from a sketch on a drawing pad to becoming one of the most used peripherals today. We’ll also peek into the future at some of the changes in store for the mouse and other input devices.

  Mouse Origins. Engelbart began envisioning the idea of a mouse in the early 1950s. He built upon that idea by sketching drawings over the next several years. By 1963, those drawings became a reality as Engelbart and several colleagues at the SRI (Stanford Research Institute) constructed the first mouse. That prototype was a wooden, box-shaped object with one red button on top. (A later model included three buttons. Engelbart wanted to add more buttons, but there wasn’t enough room to do so.) Underneath its wooden frame were two large wheels used to chart horizontal and vertical motion as the mouse moved across a flat surface.

In 1968, Engelbart introduced his mouse to the world as part of a demonstration regarding a networked computer system that he and his colleagues developed at SRI. His intention for the mouse (and computers in general) was very different from the purpose it serves today. He envisioned computers as an “augmentation” to human intellect and our communication abilities. Engelbart was disappointed, however, when many viewed the mouse as a tool that could merely improve office automation.

In 1970, the mouse was patented as the “X-Y Position Indicator.” (The mouse got its nickname because of its shape and long cord, which resembled the body and tail of a mouse. Even so, Engelbart and his associates didn’t intend for “mouse” to become its permanent name.)

In the 1970s, Xerox conducted more research and made additional improvements at the Palo Alto Research Center. There, emerging industry giants Steve Jobs and Bill Gates got a look at the mouse. In 1983, Microsoft built its first mouse and introduced it with the release of Word 1.0. But Microsoft only sold 5,000 of the 100,000 units built. It wasn’t until Apple released the Macintosh a year later that a mass audience viewed the mouse as a tool to make computing easier and more fun. Today, manufacturers sell hundreds of millions of mice; it’s hard to imagine a computer system without one.

  The Ever-Changing Mouse. The mice and trackballs of today are vastly different from the bulky beige two-button mice of yesteryear. Not only do they look different, but they also offer a variety of choices and options for increased functionality.

Today’s input device comes in a wide array of shapes, colors, and ergonomic designs. There are right- or left-handed models that naturally fit your hand position to help you work more comfortably. Alternately, symmetrical designs fit left- and right-handed users and all hand sizes while holding the hand in a neutral position to reduce strain and injury. New features include instant Internet access with the touch of a button and customizable buttons delivering one-click solutions to such repetitive tasks as open/close, cut/paste, or double-click.

One of the most popular innovations has been the optical mouse. Instead of having a ball on the bottom like a traditional mouse, the optical mouse has a camera. A small red light or optical sensor illuminates the surface under the mouse while a lightning-fast camera inside the mouse takes pictures. With the help of a powerful processor, the mouse determines movement by comparing each picture with the one preceding it. Microsoft’s entry into optical mice is the IntelliMouse Explorer( It comes equipped with a sensor that scans surfaces 1,500 times per second to track movement and retails for as low as $49.99.

Another recent improvement is the cordless mouse. Using batteries as a power source, it communicates with the computer via a small receiver set on the desktop. Logitech, the world’s largest manufacturer of mice, and Agilent Technologies, inventor of the optical sensor, recently unveiled the Cordless MouseMan Optical, priced at $69.95 ( It features a new power-saving optical chip that delivers twice the resolution of previous versions at 800dpi (dots per inch), providing improved accuracy on all surfaces, and is the first optical sensor of its kind to measure the amount of light reflected from the surface. When not in use, it powers down to preserve energy, resulting in prolonged three-month battery life.

“The strong success of Cordless MouseMan Optical is the marriage of these two hottest mouse technologies—cordlessness frees users from the tangled cords that once plagued their desktop, while the lack of a ball makes the mouse precise and eliminates the need for cleaning,” says Wolfgang Hausen, senior vice president and general manager of Logitech´s Control Devices Business Unit.

Another Logitech development is the iFeel MouseMan! ($59.95; http://www.logitech .com), a contoured, 4-button mouse that adds the sense of tactility to computing. When scrolling over iFeel-enabled dialog boxes, menus, navigation bars, and icons, the user experiences a variety of gentle vibrations. Included Mouseware Software and the use of Internet Explorer 5.0 or higher are required.

Kensington's latest-and-greatest offering is the Turbo Mouse Pro, now Mac OS X compatible—the first trackball to incorporate drivers that will work with OSX. A wireless version will be available in August. The Turbo Mouse Pro also has six Direct Launch buttons, four large programmable function buttons and a scroll wheel. Says Ian Lombard, senior product manager, Kensington Technology Group. "It's probably the most versatile trackball on the market today for Mac users. I don't know of any other input device that comes close in functionality, performance and quality."

Microsoft's IntelliMouse Explorer model is an optical mouse that uses IntelliEye technology to omit the need for moving parts or a special mousepad.
Other manufacturers are experimenting with different takes on the traditional mouse. The NoHands Mouse from Hunter Digital ( offers an alternative designed to combat the problem of repetitive wrist stress and strain. The NoHands Mouse ($289.95 direct from the company) consists of two interlinked footpads that respond to pressure from your feet. And the ScrollPoint Pro Mouse is IBM’s new contour-shaped pointing device built on the “red eraser” navigator from its TrackPoint cursor control on notebooks. The new ScrollPoint supports 360-degree fingertip scrolling, Internet scroll command, as well as autoscroll, and a fully programmable thumb button.

  Forward To The Future. Ken Hinckley, research scientist at the Adaptive Systems & Interaction Group of Microsoft Research, sees two inventions taking center stage in coming years. The TouchMouse is a prototype mouse that can sense when the user touches or releases the mouse or a button on it. “Touch-sensing devices such as the TouchMouse use unobtrusive capacitance sensors to detect contact from the user’s hand,” says Hinckley. “Touch sensing might be used to adapt the user interface depending on what the user is doing. For example, toolbars can fade out when the user is not using the mouse, or special-purpose displays can appear when the user touches a dedicated secondary device.”

A second project, the VideoMouse, is capable of sensing motion in 3-D because its input sensor is a built-in camera. “By default, this mouse behaves just like a regular mouse, but it is also capable of sensing motion in 3-D, including regular 2-D mouse motion, tilt in the forward/back and left/right axes, rotation of the mouse about its vertical axis, and some limited height sensing,” Hinckley says.

In addition, Lombard says the future of mice will include "high end Macintosh mice to improve ease of use for visual/graphic design applications, more wireless products, more force feedback trackballs and mice, higher precision optical mice."

Another innovation on the horizon is a cordless mouse based on Bluetooth wireless technology. Logitech has already announced plans to add Bluetooth connectivity and compatibility, with other manufacturers sure to follow.

Still other possibilities for the future include optical sensoring, with tiny cameras following the user’s eye movements to control functions on the computer. It may be someday possible to move the cursor on your screen simply by moving your eyes.

Although mouse technology is constantly improving and evolving, no one foresees extinction for the little critter that put the computer revolution into the palms of our hands. Until something more user-friendly comes along, the mouse will continue to be the faithful companion of computer users around the world.  

by Blaine Flamig and Natalie Whitlock

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