20.2 Mouse Characteristics

Here are the important characteristics of mice and trackballs:


Mice are available that use the following mechanisms:


Mechanical mice use a rubber-coated ball that contacts the mouse pad. Moving the mouse causes the ball to move, which in turn causes one or both of the internal cylindrical rollers with which the ball is in contact to move. These two internal rollers are oriented at 90° to each other, which allows one to respond to horizontal mouse movement and the other to vertical mouse movement. Connected to the end of each roller is a wheel with many small notches around its circumference. As the wheel rotates, these notches alternately pass or block light from an LED aimed to impinge on a sensor. The rate at and duration for which the sensors see the light flickering correspond to how fast, how far, and in what direction the ball is moving.

Modern mechanical mice are inexpensive and reliable, but require frequent cleaning. The improvements in second-generation optical mice, described next, have largely relegated mechanical mice to bargain-basement systems.


Early mechanical mice provided limited resolution, were relatively unreliable, and required very frequent cleaning. Manufacturers addressed these problems by introducing optical mice, which substituted an optical sensor for the mouse ball. Reducing the number of moving parts increased reliability, and because the optical mouse was a sealed unit, cleaning was needed much less often. But first-generation optical mice had two drawbacks. First, their relatively primitive sensors required a special mouse pad that contained an embedded mesh of very fine wires and was easily damaged. Second, they were much more expensive than mechanical mice. As mechanical mice continued to improve, optical mice gradually became niche products and disappeared from the market for several years.

A few years ago, Microsoft introduced second-generation optical mice that use enhanced sensors and more powerful laser diodes, which Microsoft calls IntelliEye technology. We call them red-eye mice. Because they are more sensitive and use a brighter light source, these mice can detect very minor variations in surface texture. That allows them to work on nearly any surface from a standard mouse pad to a bare desktop. In fact, they work on everything we've tried except a mirror. We've even used them successfully on featureless beige computer cases and unmarked sheets of white paper. Because they are sealed units, they do not require routine cleaning, which is a blessing for people who eat, drink, or smoke at their desks.

At first, IntelliEye mice were much more expensive than mechanical mice, but that price premium nearly disappeared as other manufacturers began shipping similar models. Basic red-eye mice now sell for $15, which has killed the market for mechanical mice. We now use only red-eye mice, and recommend them exclusively.

Because some red-eye mice draw more current than mechanical mice, they may be incompatible with some systems. In particular, some notebook computers have underpowered PS/2 ports that cannot drive some red-eye mice. Also, many KVM switches do not function properly or at all with red-eye mice.


At least one type of mouse doesn't require any mousing surface at all. Gyration's Ultra Cordless Optical Mouse can be used as a standard optical mouse when there is a mousing surface available. If there isn't, you can enable gyroscopic mode (at a substantial penalty in battery life) and simply wave the mouse around in midair. The built-in gyroscopes detect the mouse movements and translate them into pointer movements on screen. This capability doesn't come cheaply. A basic model with a 25-foot range sells for $70 or so, and models with longer ranges cost correspondingly more.

Number of buttons

Unlike the Macintosh world, where one-button mice are the rule, PC mice typically have two buttons, and some have three or more. In addition, many mice have a scroll wheel, which can function as another button. Using anything beyond the standard two buttons requires that both the driver and the application support the additional buttons. For example, the extended functions of the Microsoft Wheel Mouse are available only in applications that are specifically written to implement those extended functions, and only then if the enhanced mouse driver is installed to replace the standard mouse driver.


Mice have been produced in four interfaces. In relative order of current popularity, these interfaces include:


The PS/2 mouse uses the same mini-DIN physical connector as the PS/2 keyboard, and interfaces to the PC using a second msi8042. But the mouse port uses IRQ12?versus IRQ1 for the keyboard port?which means that the mouse port and keyboard port are not interchangeable. All ATX motherboards provide a PS/2 mouse port on the I/O panel. Late model AT and Baby AT motherboards provide a PS/2 mouse port in the form of header pins on the motherboard, and use a port extender cable to jumper the header pins to a port connector on the back panel. The arrangement and pinouts of that header-pin connector are not standard. We have seen motherboards that use five-pin inline connectors, six-pin inline connectors, and 2x3 rectangular connectors. Even motherboards that use the same physical connector may use different pinouts. Most AT motherboards include a matching port extender. If yours does not, verify the pinouts in the motherboard manual before purchasing an extender.


A USB mouse uses no special resources beyond those claimed by the USB host controller itself. Unlike USB keyboards, USB mice do not require BIOS support because they need not be accessible until the operating system has loaded. They do require an operating system, such as Windows 9X/2000/XP or Linux, that supports USB. Many current mice offer the USB interface, and usually include an adapter to allow the mouse to be connected to a standard PS/2 mouse port.


Most AT and Baby AT motherboards from 1995 and earlier do not include a PS/2 mouse connector. With these systems, you normally use a serial mouse. A serial mouse uses a standard DB9F connector, and connects to a DB9M serial port connector on the PC. A serial mouse uses no special resources other than the standard serial port resources for the port to which it is connected (IRQ4 and base address 03F8-03FF for COM1, or IRQ3 and 02F8-02FF for COM2). You can connect a serial mouse to either serial port. When the mouse driver initializes, it detects which port the mouse is connected to and uses the appropriate IRQ and base address to access it. Serial mice are obsolete, although many remain in service on older systems.


A bus mouse (also called an InPort mouse) is so named because it connects to an adapter that plugs into the expansion bus. Bus mice were introduced to allow connecting a mouse to a PC that had no free serial ports. The adapter card is an 8-bit ISA card that provides selectable IRQ (usually 2, 3, 4, or 5) and base address settings. However, as an 8-bit card, it is limited to using 8-bit IRQs, most or all of which are already in use on a PC with two active serial ports, which is the reason for using a bus mouse in the first place. Ordinarily, the only available choice is IRQ5. If the system has an 8-bit sound card installed, IRQ5 is also occupied, which leaves no alternative unless you are willing to disable the IRQ for LPT1. Bus mice and InPort adapters are obsolete.

None of these interfaces is compatible with any of the others, although some mice are designed with autosensing circuitry to allow them to work with more than one interface. Dual compatibility is usually listed on the bottom of the mouse?e.g., "Serial and PS/2 compatible" or "USB and PS/2 compatible." In particular, be careful about interchanging PS/2 and bus mice, which use the same connector. Connecting a PS/2 mouse to a bus mouse port or vice versa can damage the mouse, the PC, or both.