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Adding PCI cards
22 - English A26361-D1961-Z120-1-7419, edition 2
PCI bus interrupts - Selecting correct PCI slot
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To achieve optimum stability, performance and compatibility, avoid the multiple use of
ISA IRQs or PCI IRQ Lines (IRQ sharing). Should IRQ sharing be unavoidable, then all
involved devices and their drivers must support IRQ sharing.
PCI IRQ Lines connect AGP slots, PCI slots and onboard components to the interrupt controller.
PCI IRQ Lines are permanently wired on the mainboard.
Which ISA IRQs are assigned to the PCI IRQ Lines is normally automatically specified by the BIOS
(see description in "BIOS Setup").
Monofunctional expansions cards:
Standard AGP and PCI expansion cards require a maximum of one interrupt, which is called the PCI
interrupt INT A. Expansion cards that do not require an interrupt can be installed in any desired slot.
Multifunctional expansion cards or expansion cards with integrated PCI-PCI bridge:
These expansion cards require up to four PCI interrupts: INT A, INT B, INT C, INT D. How many and
which of these interrupts are used is specified in the documentation provided with the card.
The assignment of the PCI interrupts to the PCI IRQ Lines is shown in the following table:
Controller or slot INT
Mechanical slot
On board controller
1 2 3 4
USB 1.1 AC97 PCI slot
Chips
et
INT
LINE
1
st
2
nd
3
rd
USB 2.0
IDE
Audio
Modem
LAN
AGP
1 2 3
1 (A) - - - - + - - - A B C D - - -
2 (B) - - - - - - - - B C D A - - -
3 (C) - - - - - + + - - D A B - - -
4 (D) - - - - - - - + - A B C - - -
5 (E) + - - - - - - - - - - - - - -
6 (F) - + - - - - - - - - - - - - -
7 (G) - - + - - - - - - - - - - - -
8 (H) - - - + - - - - - - - - - - -
Use the first PCI slots that have a single PCI IRQ Line (no IRQ sharing). If you must use another
PCI slot with IRQ sharing, check whether the expansion card properly supports IRQ sharing with the
other devices on this PCI IRQ Line. The drivers of all cards and components on this PCI IRQ Line
must also support IRQ sharing.