HP XM600 - Kayak - 128 MB RAM Technical Reference Manual page 117

5 HP BIOS
BIOS Addresses
There are three major interrupt modes available:
PIC mode: This "Legacy" mode uses only the interrupt controllers.
Therefore, only one processor can be supported in this mode. This mode
can be selected upon installation of Windows NT.
Virtual wire mode: This mode is implemented using the 82C59 interrupt
and the I/O APIC controller and is 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 operations.
Symmetric I/O mode: This mode is implemented using the I/O APIC
controller 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.
117