Asus P I-AP55T P/I-AP55T User's manual - Page 23

Upgrade Guide Assigning System IFlils 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 IDE 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 requires that an IRQ it will use be configured on the card hardware. "Plug and Play" ISA cards can use an ISA Configuration Utility to determine and assign an available IRQ. 2 - 3