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System BIOS

BIOS Addresses

Chapter 3

Three major interrupt modes are available:

• PIC mode: This mode uses only legacy interrupt controllers, so the system can

support only one processor. You can select this mode when you install Windows NT.

• Virtual wire mode: This mode, which is implemented using the 82C59 interrupt

and the I/O APIC controller, 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, PCI interrupts are routed to the INT line. In

symmetric I/O mode, PCI interrupts are routed to the I/O APIC controllers and

forwarded over an APIC bus to the processors.

PCI IRQ Lines

PCI devices generate IRQs using up to four PCI IRQ 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 60 for a table of the PCI device interrupts.

INTIN18 PCINTC

INTIN19 PCINTD

INTIN20 TFPC IRQ

INTIN21 SCI IRQ

INTIN22 not

connected

INTIN23 ICH SMI

(not used)

I/O APIC Input IRQ IRQ Description

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Hp A7818-IE002 Manuel d'utilisateur Page 76