[ The PC Guide | Systems and Components Reference Guide | Motherboard and System Devices | System Resources | Plug and Play ]

Plug and Play Operation

Most of the actual work involved in making Plug and Play function is performed by the system BIOS during the boot process. At the appropriate step of the boot process, the BIOS will follow a special procedure to determine and configure the Plug and Play devices in your system. Here is a rough layout of the steps that the BIOS follows at boot time when managing a PCI-based Plug and Play system:

1. Create a resource table of the available IRQs, DMA channels and I/O addresses, excluding any that are reserved for system devices.
2. Search for and identify PnP and non-PnP devices on the PCI and ISA buses.
3. Load the last known system configuration from the ESCD area stored in non-volatile memory.
4. Compare the current configuration to the last known configuration. If they are unchanged, continue with the boot; this part of the boot process ends and the rest of the bootup continues from here.
5. If the configuration is new, begin system reconfiguration. Start with the resource table by eliminating any resources being used by non-PnP devices.
6. Check the BIOS settings to see if any additional system resources have been reserved for use by non-PnP devices and eliminate any of these from the resource table.
7. Assign resources to PnP cards from the resources remaining in the resource table, and inform the devices of their new assignments.
8. Update the ESCD area by saving to it the new system configuration. Most BIOSes will print a message when this happens like "Updating ESCD ... Successful".
9. Continue with the boot.

Tip: See the section on PCI / PnP in the BIOS area, which describes the BIOS settings that affect how PnP works in a PCI system.

Next: Extended System Configuration Data (ESCD)

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