A PCI bridge resource in the I/O hardware which provides for the connexion of PCI adapters to the system PCI I/O bus. Each PCI adapter connected under a multi-adapter bridge is controlled individually by the multi-adapter bridge. The multi-adapter bridge number identifies a multi-adapter bridge on a given system PCI I/O bus and is part of the Direct Select Address for a PCI I/O adapter. The bus number and the multi-adapter bridge number together identify a unique multi-adapter bridge in the system.