Units are needed to follow a protocol so the interrupt-ask for (IRQ) strains might be shared. The PCI bus consists of four interrupt traces, INTA# through INTD#, all of which can be found to each machine. Around eight PCI equipment share the identical IRQ line (INTINA# by INTINH#) in APIC-enabled https://nathanlabsadvisory.com/nesa-compliance/