PC Hardware in a Nutshell, Second Edition

System Resources

PCs have four types of system resources—Interrupt Request lines, DMA channels, I/O ports, and memory ranges. Many system components and peripherals require one or more of these resources, which raises the twin problems of resource availability and resource conflicts. Resource availability is particularly important with regard to IRQs, which are in high demand, and of which only 16 exist. Resource conflicts can occur when two devices are assigned the same resource, in which case one or both devices may not function or may function unpredictably. Resource conflicts may occur even with plentiful resources, such as I/O ports, where many are available and only a few are in use.

A frequent cause of problems when building or upgrading PCs is a shortage of required resources or unintentional resource conflicts that occur when a new component is installed that was inadvertently configured to use a resource already in use. Two technologies, PCI and Plug-N-Play, used in conjunction with recent versions of Microsoft operating systems (Windows 95 OSR2, Windows 98, and Windows 2000/XP) go a long way toward extending the availability of resources and preventing conflicts. Even in such an ideal environment, however, resource conflicts sometimes occur, particularly if you are using older “legacy” hardware. The following sections describe what you need to know about PC resources and how to manage them.

Interrupt Request Line (IRQ)

When a component or peripheral, such as a network ...