HP Kayak XU800 Technical Reference Manual page 70

2 System Board
Assigned Device Interrupts
Virtual wire mode: This mode is implemented with APIC controllers in the
ICH and P64H and used during boot time. The virtual wire mode allows the
transition to the "symmetric I/O mode". In the virtual wire mode, only one
processor executes instructions.
Symmetric I/O mode: This mode is implemented with APIC controllers in
the ICH and P64H, and allows for multiple processor operations.
NOTE In "PIC mode" and "virtual wire mode", the PCI interrupts are routed to the
INT line. In the "symmetric I/O mode", the PCI interrupts are routed to the
I/O APIC controllers and forwarded over an APIC bus to the processors.
PCI Interrupt Request Lines
PCI devices generate interrupt requests using up to four PCI interrupt
request lines (INTA#, INTB#, INTC#, and INTD#).
PCI interrupts can be shared; several devices can use the same interrupt.
However, optimal system performance is reached when minimizing the
sharing of interrupts. Refer to page 68 for a table of the PCI device
interrupts.
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