Products are needed to adhere to a protocol so that the interrupt-request (IRQ) lines might be shared. The PCI bus includes four interrupt lines, INTA# by way of INTD#, all of which can be obtained to every gadget. Around 8 PCI products share the same IRQ line (INTINA# via INTINH#) https://nathanlabsadvisory.com/pci-dss-training/