Irq Functionality - FIC PT-2006 Manual

PT-2006 Mainboard Manual

IRQ Functionality

As you read through this manual, you will see the term IRQ on a number of
occasions. It is important for you to know what this term means, particularly if
you intend to upgrade your system.
IRQ stands for Interrupt Request, the process in which an input or output device
tells the processor to temporarily interrupt its current task and immediately
process something from the source of the interrupt. When it has completed this,
the processor returns to the task it was already processing. Devices that need an
IRQ line to operate sometimes need to have exclusive use of that line.
A large number of add-on cards, such as sound cards and LAN cards, require the
use of an IRQ line to function. There is a total of 16 IRQs (IRQ0 to IRQ15)
available in a system, although some of them may already be in use by
components in the system such as the keyboard and mouse. Add-on cards that
need to use an IRQ draw from the unused group of IRQs. When installing a card
that uses an IRQ, it will have a default IRQ setting which you might have to
change if that IRQ is already in use and cannot be shared.
Both ISA and PCI add-on cards may need to use IRQs. System IRQs are
available to add-on cards installed on the ISA bus first; the remaining ones can
be used by cards installed on the PCI bus. There are two categories of ISA add-
on cards: so-called Legacy ISA cards, which need to be configured manually and
then installed in any available ISA slot; and Plug and Play (PnP) ISA cards,
which are configured automatically by the system. As a result, when you install
Legacy ISA cards, you have to carefully configure the system to ensure that the
installed cards do not conflict with each other by having the same IRQ. With PnP
cards, on the other hand, IRQs are assigned automatically from the ones
available in the system. In the case of PCI add-on cards, the BIOS automatically
assigns an IRQ card to the PCI slot the card is installed in.
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