Asus P/I-AP55T - Manual (Page 23)

upgrade Guide
Assigning System IRQs for Expansion Cards
Cards for both the ISA and PCI buses may need to use IRQs. You
must configure any IRQ assignments so that the system can know
which IRQ is assigned to which card. IRQs must be assigned correctly
or the mainboard will not work properly.
As mentioned in Chapter 1, there are 16 IRQs. Some of them are
already in use by standard parts of the system such as the keyboard
or mouse. IRQs 5,10 and 11 are not used by the mainboard and are
available. IRQ 15 is also available if you disable the Secondary ГОЕ
channel.
IRQs are available to either bus. The two bus designs deal with
IRQs differently however. For PCI cards that use an IRQ, the BIOS
will auto-assign an IRQ from the available IRQs when the slots are
set to "Auto" in the BIOS Setup Utility. See the section on PCI And
PNP Setup in Chapter 3. The BIOS will not auto-assign an IRQ for a
PCI slot if there is no card installed in the slot and or the card does
not use an IRQ.
For ISA cards there are two methods. A "Legacy" ISA card re­
quires that an IRQ it will use be configured on the card hardware.
"Plug and Play" ISA cards can use an ISA Configuration UtiUty to
determine and assign an available IRQ.
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