K7VAT
System Board 27
2.
Now the BIOS assigns the PCI interrupts from the remaining interrupts in the pool.
The interrupts are assigned in the A, D, B, C order. (With other words, the AGP IRQ
is first assigned, then the USB IRQ with the others trailing). The USB, VGA and
ACPI IRQs can be disabled in the BIOS as mentioned before.
B
PnP OS Installed: Yes
The BIOS will only assign the PCI interrupts. The
interrupts are assigned in the same order as mentioned above.
After assigning the interrupts control is passed to the OS. The OS will now assign the ISA
PnP interrupts from the remaining IRQs in the pool. However, since ISA PnP cards pass the
OS a list of IRQs that can be assigned to it, if the OS finds that all the IRQWs on the list are
already assigned, it may reassign an IRQ that was assigned to PCI by the BIOS. This means
concretely that the OS can change BIOS settings, and that settings made in the BIOS are
not necessarily correct when using a PnP OS.
