SYSTEM EXPANSION

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.

IRQDefault assignmentAvailable?

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.

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