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ASUS P4B-MX motherboard user guide
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IRQ XX Reserved [No/ICU]
These fields indicate whether or not the displayed IRQ for each field is
being used by a legacy (non-PnP) ISA card. The setting [No/ICU] for an
IRQ field indicates that you are using the ISA Configuration Utility (ICU),
and that this particular IRQ is NOT required by a legacy ISA card. Set the
IRQ field to [Yes] if you install a legacy ISA card that requires a unique IRQ
and you are NOT using ICU. Configuration options: [No/ICU] [Yes]
4.4.3.2 PCI IRQ Resource Exclusion