Interrupt request

In computing, an interrupt request (IRQ) is a phrase used to refer to either the act of interrupting, the bus lines used to signal an interrupt, or the interrupt input lines on a Programmable Interrupt Controller (PIC). Interrupt lines are often identifed by an index with the format of IRQ followed by a number.

For example, on the Intel 8259 family of PICs there are eight interrupt inputs commonly referred to as IRQ0 through IRQ7. In x86 based computer systems that use two of these PICs, the combined set of lines are referred to as IRQ0 through IRQ15. Technically these lines are named IR0 thorugh IR7, and the lines on the ISA bus to which they were historically attached are named IRQ0 through IRQ15.

Newer x86 systems integrate an APIC that conforms to the Intel APIC Architecture. These APICs support a programming interface for up to 255 physical hardware IRQ lines per APIC, with a typical system implementing support for only around 24 total hardware lines.

See Intel 8259 for a common list of hardware IRQ lines in x86 systems.

See also

• Advanced Programmable Interrupt Controller
• Programmable Interrupt Controller
• Intel 8259

• Interrupt Handler

References

• Gilluwe, Frank van. The Undocumented PC, Second Edition, Addision-Wesley Developers Press, 1997. ISBN 0-201-47950-8
• Shanley, Tom. ISA System Architecture, Third Edition, Addison-Wesley Publishing Company, 1995. ISBN 0201409968
• Solari, Edward. PCI & PCI-X Hardware and Software Architecture & Design, Sixth Edition, Research Tech Inc., 2004. ISBN 0976086506