Devices are needed to observe a protocol so that the interrupt-request (IRQ) lines can be shared. The PCI bus features four interrupt strains, INTA# by way of INTD#, all of which are available to every unit. Up to 8 PCI devices share a similar IRQ line (INTINA# by INTINH#) in https://nathanlabsadvisory.com/cybersecurity-technical-writing/