HP Vectra XU5 Reference Manual page 56

PCI Interrupt Request Lines
PCI devices generate interrupt requests using up to four PCI interrupt request lines (INTA#,
INTB#, INTC#, and INTD#).
When a PCI device makes an interrupt request, the request is redirected to the system
interrupt controller. The interrupt request will be redirected to one of the IRQ lines made
available for PCI devices.
All PCI devices with interrupt transfer support will use and share INTA#. A PCI device
supporting multiple functionalities may support several INT lines (for example, the
LAN/SCSI-2 controller uses INTA# and INTB#). These devices will also require more than
one system interrupt request line.
Vectra XU Technical Reference Summary of the HP BIOS 56