Equipment are needed to adhere to a protocol so that the interrupt-request (IRQ) lines could be shared. The PCI bus incorporates 4 interrupt strains, INTA# by means of INTD#, all of which can be obtained to every device. Around 8 PCI products share a similar IRQ line (INTINA# via INTINH#) https://nathanlabsadvisory.com/ncema-7000-2015-certification/