Products are needed to comply with a protocol so that the interrupt-request (IRQ) strains can be shared. The PCI bus includes four interrupt strains, INTA# by way of INTD#, all of which are available to each product. Approximately 8 PCI units share precisely the same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/spear-phising/