Hardware Reference
In-Depth Information
PnP BIOS
Originally, installing and configuring devices in PCs was difficult. During installation, the user was
faced with the task of configuring the new card by selecting the IRQ, I/O ports, and DMA channel. In
the past, users were required to move jumpers or set switches on the add-in cards to control these
settings. They needed to know exactly which resources were already in use so they could find a set of
resources that did not conflict with the devices already in the system. If a conflict existed, the system
might not boot, and the device might fail or cause the conflicting hardware to fail.
PnP is technology designed to prevent configuration problems and provide users with the capability
to easily expand a PC. With PnP, the user simply plugs in the new card, and the system configures it
automatically for proper operation.
PnP is composed of three principal components:
• PnP BIOS
• Extended System Configuration Data (ESCD)
• PnP OS
The PnP BIOS initiates the configuration of the PnP cards during the bootup process. If the cards
previously were installed, the BIOS reads the information from ESCD, initializes the cards, and boots
the system. During the installation of new PnP cards, the BIOS consults the ESCD to determine which
system resources are available and needed for the add-in cards. If the BIOS is capable of finding
sufficient available resources, it configures the cards. However, if the BIOS is incapable of locating
sufficient available resources, the PnP routines in the OS complete the configuration process. During
