A mouse is a small, simple device that you push over the mouse pad on your desktop to control the on-screen cursor or pointer. A trackball, however, is an inverted mouse with an exposed ball. Move the ball and it moves the on-screen cursor in the same way a mouse does. The ball is positioned inside a frame with sensors to detect its movements. To understand better how a trackball works, turn over your mouse and move the cursor across the screen by moving the ball with your thumb. It may seem awkward at first, but with practice you can quickly become accustomed to it. 

Both devices perform basically the same functions; they just differ in their mechanics and number of buttons. Trackballs are excellent for space-constrained areas and require just about as much maintenance as mice. (Though many trackball manufacturers will tell you they are maintenance-free, they must be cleaned regularly to remove dust and contaminants that build up on the ball or sensors.) 

Why would I need it?
As mentioned, a mouse is standard issue for any desktop computer, but they are available for notebook computers, too, often as an upgrade or option. For basic computing, a mouse is sufficient. However, because of the increased movements required to operate a mouse, anyone who spends a large amount of time at their computer might want to consider the more ergonomically correct trackball. To control a trackball, simply move the ball with your thumb and click on the buttons with your fingers. 

If your current mouse or trackball does not include a wheel feature, you may want to consider upgrading to a "wheel-mouse" or trackball with a wheel. The wheel allows you to scroll through computer applications without having to drag the scroll bar up and down, reducing the amount of movements necessary to complete a task. 

How do I install and use it?
Before installing any computer hardware, carefully read the included instructions before proceeding. Also be sure the computer's power is turned off before connecting any devices. 

Connect your mouse or trackball to its compatible port. Both offer three interface options: USB (Universal Serial Bus), serial port, or PS/2 port. Most serial and PS/2 compatible mice offer adapters so you can use either interface. Carefully review the product documentation to determine if this is the case for you. 

USB:USB ports look like a large telephone jack and offers the advantage of "hot-swapping." This means you do not have to turn off your computer and re-boot it each time you want to switch between USB devices. Connect the mouse to an available USB port and install the driver software. Windows 98 will do most of the installation work for you. A USB interface is ideal for a shared computer where users' hardware preferences might differ. 

Serial Port:A 9-pin port, also known as RS-232, the serial port is often a dedicated mouse port. Connect the mouse to the serial port, re-boot your computer, and place the driver software into its appropriate drive, either CD-ROM or floppy disc. Windows 95 and 98 will recognize the new hardware and complete the installation after your computer boots up. 

PS/2:A 6-pin, round connection, is the more common interface for mice and keyboards. It is the slowest port of the three and is usually reserved for mice and keyboards since they don't need the speed to process large amounts of data. Many PS/2 devices include pass-through ports so that you can add more than one in the event that you have only one available PS/2 port. After connecting the mouse or trackball, insert the driver disc into the appropriate drive and restart your computer. Windows 95 and Windows 98 systems will do the rest for you. 

Customize the buttons with software:You can customize your mouse or trackball to your preferences or needs. Use your mouse control panel to change the tracking speed, adjust the time interval for double clicking, and use a click function to lock the drag control and swap over the buttons for right and left hands. The software that comes with a three-button mouse allows you to easily program the middle button to do certain tasks. The middle button can be used as a double click. Many people find pushing the middle button once is much easier than trying to double click the other button. This is also be good for children, who seem to have a hard time with the double click. 

Using the trackball:You move the ball with your thumb, fingers, palm, or a combination of them. In turn, this moves the cursor around the screen. A trackball generally takes some time to get used to at first, but many users prefer using a trackball because of the greater control and precise movements it can carry out. A trackball does not need to sit on a flat surface, such as a mouse pad, and it offers greater flexibility in its use. This is especially useful for those of you who spend much of your time in front of your computer, such as graphic designers or hardcore gamers. 

Clean it!The mouse ball and trackball both collect dust and its motion can be improved with regular cleaning. Just turn the mouse upside down and release the ball from its slot to remove the dust. A trackball usually requires the removal of anchor screws from the base and removing the ball to clean out dust and other contaminants that may hinder its performance. Most manufacturers say trackballs are maintenance free, but they do usually require occasional cleaning. 

How do I go about buying one?
Before buying, determine what you want to use it for. This should help you narrow down what type of mouse you may need and how much you'd like to spend. A large number are available, including specific ones for right- or left-handers, different sizes to match different hand sizes, and different mice for different functionality levels. 

There are three basic types of mice: mechanical, opto-mechanical and optical. A mechanical mouse has a rubber or metal ball on its underside that rolls in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly. An opto-mechanical mouse is similar to a mechanical mouse, but uses optical sensors to detect motion of the ball. And an optical mouse uses a laser to sense the mouse's movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and opto-mechanical mice, but they are also more expensive. 

Function:Note down a few ideas of which functions are most important for your mouse to include. If it's just for simple and straightforward operation of click, double click, and drag, you may want to purchase a lower-priced, two-button mouse. For quick scrolling and panning through business documents, a wheel mouse or trackball might be a good idea. If you or your kids were going to use it for games, you might want a mouse with force feedback, which allows your hands to "feel" what your eyes are seeing on the screen. Many gamers prefer trackballs for greater precision and comfort. The high-end, more expensive mice allow you to optimize the functionality of your mouse with special features and an added third button. 

Form: There is a great variety of mouse shapes, from "ergonomic" to hockey-puck to pistol-shaped mice. The most important factor: buy what feels comfortable in your hand. If ergonomics is a deciding factor in upgrading, seriously consider a trackball. 

Size:To begin, you need a mouse that's sized for you. Don't select a mouse that requires stretching of the fingers in order to hold on; the result can be hand fatigue. In general, sometimes a mouse that seems smaller than you can handle will provide more comfortable use. A good rule of thumb is to choose a mouse that isn't much wider than your first three fingers held closely together. 

Cord Length:Don't pick a mouse with a short cord. Most mouse makers have the sense to put a 6-foot (2-meter) cord on their mice, but some cheaper models are made with shorter cord, so be careful. 

Resolution:Resolution is the smallest movement that the mouse can distinguish, usually measured in dots per inch. Hence, a 300dpi mouse can detect movements of as little as 1/300th of an inch, while a 525dpi mouse can detect movements of 1/525th of an inch. Most modern mice fall between 350dpi and 600dpi. Higher resolutions mean that you can tune the mouse up to a faster speed and get cleaner, higher precision cursor placement. 

Number of Buttons:Typically, there are two buttons. Three will allow you the option to program things for the middle one. Having only one button does however limit your capabilities. Macintosh mice usually have one button. Trackballs can have as many as four. 

Wheel:Fairly new to the mouse and trackball worlds, a wheel is a great addition. In fact, once you get used to it you'll wonder what you ever did without one. A wheel allows you to scroll through windows without having to located and drag the scroll bar. It's a must have for avid computer and Internet users.