Products Are required to abide by a protocol so that the interrupt-request (IRQ) traces may be shared. The PCI bus includes four interrupt lines, INTA# via INTD#, all of which are available to every product. Approximately eight PCI products share the identical IRQ line (INTINA# through INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/security-program-advisory/