Asus P55SP4 - Manual (Page 23)

P/I-P55SP4 User's Manual
Assigning System IRQs for Expansion Cards
Some expansion cards need to use an IRQ to operate. Generally
an IRQ must be exclusively assigned to one use. As mentioned in
Chapter 1, there are 16 IRQs available. In an standard design, some
of them are already in use by parts of the system such as the keyboard
or mouse. Expansion cards that need to use an IRQ then draw from
the unused group of System IRQs.
Both ISA and PCI expansion cards may need to use IRQs. Sys­
tem IRQs are available to cards installed in the ISA expansion bus
first, and any remaining can be used by cards installed on the PCI bus.
Currently, there are two types of ISA cards. The original ISA expan­
sion card design, now referred to as "Legacy" ISA cards, requires that
you configure the card hardware manually and then install it in any
available slot on the ISA bus. Under this scheme, you must ensure
that the installed cards do not conflict with each other by using the
same IRQ. This process requires careful manual system configuration
to avoid conflicts that prevent the system from working properly.
To address this problem, the Plug and Play specification was
developed to allow automatic system configuration whenever a Plug
and Play-compliant card is added to the system. For Plug and Play
(PNP) cards, IRQs are assigned automatcally from those available.
If the system has both Legacy and PNP ISA cards installed, IRQs
are assigned to PNP cards from the IRQs not already hardware as­
signed to the Legacy cards. In this case, you can establish the system
confguration in one of two ways. If you have an ISA Configuration
Utility, you can use it to indicate which IRQs are in use by Legacy
cards. If you do not have an ICU program, you can use the PCI and
PNP Configuration of the BIOS Setup utility to indicate which IRQs
are being used by Leagacy cards. Refer to Chapter 3 for information
on how to do this.
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