Gadgets are needed to comply with a protocol so which the interrupt-ask for (IRQ) lines is often shared. The PCI bus involves 4 interrupt lines, INTA# by INTD#, all of which are available to each machine. Around 8 PCI devices share the exact same IRQ line (INTINA# via INTINH#) in https://nathanlabsadvisory.com/bespoke-training/