Plug and Play Resource Assignments
Plug and Play (PnP) is a device configuration feature that must be supported by the oper-
ating system, chipset, and BIOS on the PC. With this support, a new hardware device that
is attached to a port or an expansion slot connected directly to the motherboard can be au-
tomatically detected and configured for system resource assignments.
However, PnP is not without its problems, not the least of which are IRQ conflicts.
PnP is limited to those IRQs that have been designated for PCI/PnP use. The system is
limited to PCI/PnP and legacy ISA devices. PnP does not work on legacy ISA devices. By
the way, all PCI devices are PnP devices, but not all PnP devices are PCI. Should a new
device require a certain IRQ, or should the system run out of available IRQs to assign,
PnP cannot itself overcome the problem. In these cases, the device will be added to the
system (and listed on the Device Manager) but will be flagged with a symbol (either a yel-
low exclamation point or a redX) to indicate a problem exists.Programmable Interrupt Controllers
Interrupt requests (IRQs) are handled by two special integrated circuits called program-
mable interrupt controllers (PICs) that are integrated in the PC’s chipset, along with
many other devices (see Chapter 5 for more information on chipsets). Each PIC contains(^296) PC Hardware: A Beginner’s Guide
Figure 13-10. The IRQ Steering tab of the PCI bus Properties window