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3. HARDWARE SETUP
3.7.2 Assigning IRQs for Expansion Cards
Some expansion cards need an IRQ to operate. Generally, an IRQ must be exclu-
sively assigned to one use. In a standard design, there are 16 IRQs available but
most of them are already in use, leaving 6 IRQs free for expansion cards. If your
motherboard has PCI audio onboard, an additional IRQ will be used. If your moth-
erboard also has MIDI enabled, another IRQ will be used, leaving 4 IRQs free.
The following table lists the default IRQ assignments for standard PC devices. Use
this table when configuring your system and for resolving IRQ conflicts.
Standard Interrupt Assignments
IRQ
Priority
0
1
2
N/A
3*
11
4*
12
5*
13
6
14
7*
15
8
9*
10*
11*
12*
13
14*
15*
10
*These IRQs are usually available for ISA or PCI devices.
28
Standard Function
1
System Timer
2
Keyboard Controller
Programmable Interrupt
Communications Port (COM2)
Communications Port (COM1)
Sound Card (sometimes LPT2)
Floppy Disk Controller
Printer Port (LPT1)
3
System CMOS/Real Time Clock
4
ACPI Mode when enabled
5
IRQ Holder for PCI Steering
6
IRQ Holder for PCI Steering
7
PS/2 Compatible Mouse Port
8
Numeric Data Processor
9
Primary IDE Channel
Secondary IDE Channel
ASUS CUWE-RM User's Manual
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