Over the years, they've developed trackballs, touch screens, touch pads, joystick pointers, tracking pens and dozens of other gadgets. Some have found a market, but most desktop computers still come with mice -- a testament to the durability of the original point-and-click concept.

But sooner or later, your mouse is likely to break, or you may decide you want one that's more comfortable to use. Or you may suffer from arm or wrist fatigue and decide to try your hand at some other pointing device. Here's a look at the current pointing-device technology, along with some tips for the care and feeding of your mouse.

How mice work

Mice and other pointing devices have four functions:

• First, they allow you to move your cursor around the screen.
  
• Second, they allow you to select objects and drag them from place to place using one or more buttons.
  
• Third, by double-clicking on a file or program icon, your mouse will open that file into it's associated application program.
  
• Finally, in the Windows operating system, right-clicking allows the user to access properties and submenus of a file or icon.

Mice and other pointing devices differ in the way they read your hand movements and pass the information back to your computer.

Mechanical mice
Most mice are mechanical. On the underside of the mouse is a rubber ball that protrudes slightly from a cage containing two rollers set at right angles. As you roll the ball across the desktop, it turns the rollers, which in turn send horizontal and vertical positioning information back to your computer. Those signals tell the computer to make the mouse pointer on the screen move left, right, up and down.

Optical mice
An optical mouse does not use a rolling ball. Instead, it bounces a beam of light from inside the mouse casing to a reflective pad and then back to a sensor on the mouse casing. Optical mice have no moving parts, and they're less subject to mechanical failure. However, they're limited in their movement to the boundaries of the reflective pad.

Opto-mechanical mice
These hybrids use a rubber ball to generate movement but interpret that movement with photo-interrupter discs that are turned by the internal rollers.

How the mouse communicates with your computer

Most mice communicate with a computer through a cord attached to a port on the back of the computer. Newer IBM-compatible machines have dedicated mouse ports, while older machines use a serial port. On most Macintosh computers, mice plug into the keyboard or the computer's Apple Desktop Bus port.

If you don't have room for a cord or don't want the mess, you have two choices:

• Infrared mice use an infrared transmitter to send signals back to a receiver attached to your computer's mouse port. They don't require a cord, but the mouse always has to be within the receiver's line of sight (nothing can come between the mouse and the receiver).
  
• Newer radio mice use low-power radio signals to transmit positioning information to the computer. They aren't subject to direct line-of-sight limitations and are particularly useful for making presentations that require you to be seated away from the computer.

All remote mice require batteries. Some use replaceable alkaline batteries, while others have rechargeables. If the batteries run out of power or fail, you can't use the mouse until you replace or recharge them.

Buttons, buttons and more buttons

Pressing a mouse button signals your computer that you want to do something. The software that comes with your mouse or the operating system interprets the message and acts accordingly.

Apple's designers thought people would be confused by more than one button, and they've stuck with that principle for Macintosh mice. The 100 million or so Microsoft Windows users with two- or three-button mice would contest that point of view. In any case, it's possible to buy a third-party, two- or three-, and even four- button pointing device.

If you have an IBM-compatible computer, the amount of use you'll get out of the second or third mouse buttons depends on the program you're using and your operating system. Windows OS's in particular makes extensive use of the button on the right-hand side of the mouse. For more details, see "What does a pointing device do?"

Other input devices

Although most computer users are happy with mice, there are a variety of alternatives. If you're not comfortable with a mouse, if you have special needs or if you just want to experiment, you have options:

• Trackballs. Next to the mouse, trackballs are the most popular pointing devices. Users like them because they don't take up as much room on the desktop and require less arm movement.
  
  
  Trackballs are like mice turned upside down. Instead of rolling across the desktop, the ball faces upward and you turn it with your fingers, thumb or entire palm, depending on the size of the unit. Trackball fans say they get more control of the mouse pointer with less arm fatigue than they do with a mouse. Because they're small and stationary, trackballs are frequently built into laptop computers. On the downside, trackballs can be thrown out of kilter by the oil from your skin and have to be cleaned frequently.
  
  
• Touch pads. You generally find touch pads on modern laptops. Touch pads are pads that are sensitive to the touch of your finger. Unlike other gadgets, they're true pointing devices. As you move your finger across the pad, the cursor moves. To select an object or click, just tap your finger.
  
  
• Pen input devices. Pen or stylus input devices look like their namesakes, and they're designed to mimic natural writing and drawing. They're shaped like pens and have one or more tiny buttons that correspond to mouse buttons. You move the tip of the pen across a plastic pad and select an object on the screen by tapping the point of the pen on the pad or clicking the button. Many casual users find that pens soon cause hand cramps, but some graphic artists and people working with handwriting recognition programs find them useful.
  
  
• Digitizing pads. These expensive add-ons use a mouse-like device with protruding cross hairs and a special sensitized tablet; they're used for precision work by architects, draftsmen, designers and graphic artists. Digitizing pads can be calibrated precisely for tracing existing plans and producing mechanical drawings and blueprints.
  
  
• Remote "air" mice. These specialty devices use infrared or radio signals that allow mouse operations at some distance from the computer. They're not bound to the desktop; in fact, by waving the device in the air, you can move the cursor. Remote mice are particularly useful if you're delivering a computerized presentation with an overhead projector and prefer to stand elsewhere in the room while delivering your pitch.
  
  
• Finger mice. Imagine waving your finger at the screen and seeing the cursor move. That's what finger mice do, using a tiny infrared transmitter and a receiver. The finger mouse straps onto your index finger. Theoretically, a finger mouse lets you move the mouse pointer on the screen without removing your hands from the keyboard, but it's more likely to be popular with gamers because it can record movement in three dimensions.