SYSTEM EXPANSION
3/3
ISA Interrupt request level (IRQ)
The
interrupt request level
or
IRQ
(the two terms are used
interchangeably) is the line over which the expansion card sends a
signal to get the attention of, or interrupt, the processor. Many of
these are reserved for components on the computer’s motherboard.
Some interrupts are fixed, others can be re-assigned. The following
table lists the interrupts used by the computer and shows which may
be available for use by expansion cards.
IRQ
Default assignment
Available?
IRQ0
System timer
No
IRQ1
Keyboard controller
No
IRQ2
System
No
IRQ3
Serial port 2/Remote controller
No
IRQ4
Serial port 1
Optionally
IRQ5
Audio (if fitted)
Yes
IRQ6
Diskette controller
No
IRQ7
Parallel port
Optionally
IRQ8
Real time clock
No
IRQ9
Yes
IRQ10
Yes
IRQ11
Yes
IRQ12
Mouse
No
IRQ13
Coprocessor
No
IRQ14
Primary ATA/IDE interface
No
IRQ15
Secondary ATA/IDE interface
No
With the BIOS Set-up utility IRQ4 is available if you disable serial
port1. Similarly, if you have no intention of using the parallel port,
you can disable it with the BIOS Set-up utility, completely freeing
IRQ7 for use by an expansion card.
Do not
disable ports unless you
have no intention of using them.
