Equipment are required to adhere to a protocol so that the interrupt-ask for (IRQ) lines could be shared. The PCI bus involves 4 interrupt traces, INTA# through INTD#, all of which are available to each gadget. Up to 8 PCI equipment share the same IRQ line (INTINA# by way of https://nathanlabsadvisory.com/key-components-of-a-successful-incident-response-strategy/