Late in 1996, Microsoft introduced the IntelliMouse, which differed from standard Microsoft mice by adding a small gray wheel between the mouse buttons. This was the first scrolling mouse, and since then, Logitech, IBM, and virtually all other mouse vendors have made scroll wheels or similar devices standard across almost all models, including OEM mice bundled with computer systems.

The wheel has two main functions. The primary function is to act as a scrolling device, enabling you to scroll through documents or Web pages by manipulating the wheel with your index finger. The wheel also functions as a third mouse button when you press it.

Although three-button mice have been available for years from vendors such as Logitech, the scrolling function provided a real breakthrough. No longer do you have to move the mouse pointer to click the scrollbar on the right side of your screen or take your hand off the mouse to use the arrow keys on the keyboard.

You just push or pull on the wheel. This is a major convenience, especially when browsing Web pages or working with word processing documents or spreadsheets. Also, unlike three-button mice from other vendors, the IntelliMouse's wheel-button doesn't seem to get in the way and you are less likely to click it by mistake.

Although it took a while for software vendors to support the wheel, improvements in application software and Windows support allow today's wheel mice to be fully useful with almost any recent or current Windows program. Each vendor's mouse driver software offers unique features to enhance the basic operation of the mouse.

For example, Logitech's MouseWare 9.7 driver enables you to select many uses for all three mouse buttons (the scroll wheel is treated as a third mouse button), as well as provides various options for how to scroll with each wheel click (three lines, six lines, or one screen).

Microsoft's IntelliMouse driver offers a feature called ClickLock, which allows you to drag items without holding down the primary mouse button. In addition, it offers a Universal Scroll feature that adds scrolling mouse support to applications that lack such support. To get the most from whatever scrolling or other advanced-feature mouse you have, be sure you periodically download and install new mouse drivers.

Instead of the wheel used by Microsoft and Logitech, IBM and other mouse vendors frequently use various types of buttons for scrolling. Some inexpensive mice use a rocker switch, but the most elegant of the non-wheel alternatives is IBM's ScrollPoint Pro, which uses a pressure-sensitive scroll stick similar to the TrackPoint pointing device used on IBM's notebook computer and some PC keyboards made by IBM and Unicomp.

The scrollpointer in the center of the mouse enables you to smoothly scroll through documents without having to lift your finger to roll the wheel, as you do on the Microsoft version, which makes it much easier and more convenient to use. Because no moving parts exist, the ScrollPoint is also more reliable.