Devices are needed to comply with a protocol so that the interrupt-ask for (IRQ) lines is usually shared. The PCI bus features four interrupt traces, INTA# by means of INTD#, all of which are offered to each system. Approximately 8 PCI equipment share the same IRQ line (INTINA# via INTINH#) https://nathanlabsadvisory.com/security-program-advisory/