To troubleshoot components of your PC that aren't working, it helps to know what's going on behind the scenes.
As noted at the beginning of this chapter, your PC's components require unique communication channels called IRQs (Interrupt Request Levels), reserved areas of memory called I/O addresses, and other assignments that reserve the components' places in your system. These technical settings are collectively called resources.
If your sound card occupies IRQ 11 and has an I/O address that starts at 6100, then Windows knows how to contact the card when, for example, your email software wants to play a "You've got mail" sound. If your printer also occupies these same resources, the operating system could send a sound code to printer, confusing it thoroughly and probably producing no reaction from the sound card. And it's not enough to set just a hardware component to the right channels; their drivers must be independently tuned to the same channels if they're to communicate.
Plug-and-Play technology identifies your devices and their requests for resources and referees among them. When two devices request the same resource—the same memory space, for example—Windows 2000 shifts settings in order to accommodate every element of your system. Sometimes Windows allocates a resource to more than one device, and then shuffles the resource around like an apartment shared by two people working different shifts.