Devices are needed to comply with a protocol so that the interrupt-ask for (IRQ) lines might be shared. The PCI bus includes 4 interrupt strains, INTA# by INTD#, all of which are available to every unit. As many as eight PCI products share a similar IRQ line (INTINA# by INTINH#) https://nathanlabsadvisory.com/cis-center-internet-security/