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Interrupt request
 
 
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The computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
 phrase "interrupt request" (or IRQ) is used to refer to either the act of interrupt
Interrupt

In computing, an interrupt is an asynchronous communication signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
ing the bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
 lines used to signal an interrupt, or the interrupt input lines on a Programmable Interrupt Controller
Programmable Interrupt Controller

A programmable interrupt controller is a device which allows priority levels to be assigned to its interrupt outputs. When the device has multiple interrupt outputs to assert, it will assert them in the order of their relative priority....
 (PIC). Interrupt lines are often identified by an index with the format of IRQ followed by a number. For example, on the Intel 8259
Intel 8259

The Intel 8259 is a family of Programmable Interrupt Controllers designed and developed for use with the Intel 8085 and Intel 8086 8-bit and 16-bit microprocessors....
 family of PICs there are eight interrupt inputs commonly referred to as IRQ0 through IRQ7.






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Encyclopedia


The computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
 phrase "interrupt request" (or IRQ) is used to refer to either the act of interrupt
Interrupt

In computing, an interrupt is an asynchronous communication signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
ing the bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
 lines used to signal an interrupt, or the interrupt input lines on a Programmable Interrupt Controller
Programmable Interrupt Controller

A programmable interrupt controller is a device which allows priority levels to be assigned to its interrupt outputs. When the device has multiple interrupt outputs to assert, it will assert them in the order of their relative priority....
 (PIC). Interrupt lines are often identified by an index with the format of IRQ followed by a number. For example, on the Intel 8259
Intel 8259

The Intel 8259 is a family of Programmable Interrupt Controllers designed and developed for use with the Intel 8085 and Intel 8086 8-bit and 16-bit microprocessors....
 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 through IR7, and the lines on the ISA
Industry Standard Architecture

Industry Standard Architecture was a computer bus standard for IBM compatible computers....
 bus to which they were historically attached are named IRQ0 through IRQ15.

Newer x86 systems integrate an Advanced Programmable Interrupt Controller
Advanced Programmable Interrupt Controller

An Advanced Programmable Interrupt Controller is a more intricate Programmable Interrupt Controller containing a magnitude more outputs, much more complex priority schema, and Advanced IRQ management....
 (APIC) that conforms to the Intel APIC Architecture
Intel APIC Architecture

The Intel APIC Architecture is a system of Advanced Programmable Interrupt Controllers designed by Intel for use in Symmetric multiprocessing computer systems....
. 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.

Overview


When working with computer hardware, installing and removing devices, the system relies on interrupt requests. There are default settings that are configured in the system BIOS
BIOS

In computing, the Basic Input/Output System , also known as the System BIOS, is a de facto standard defining a firmware interface for IBM PC Compatible computers....
 and recognized by the operating system. These default settings can be altered by advanced users. Modern Plug-and-play
Plug-and-play

In computing, plug and play is a term used to describe the characteristic of a computer bus, or device specification, which facilitates the discovery of a hardware component in a system, without the need for physical device configuration, or user intervention in resolving resource conflicts....
 technology has not only reduced the need for concern for these settings, but has virtually eliminated manual configuration.

x86 IRQs


See Intel 8259
Intel 8259

The Intel 8259 is a family of Programmable Interrupt Controllers designed and developed for use with the Intel 8085 and Intel 8086 8-bit and 16-bit microprocessors....
 for a common list and discussion of hardware IRQ lines in x86 systems.

Typically, 16 IRQs are used. IRQs 0 to 7 are managed by one Intel 8259 PIC, and IRQs 8 to 15 by a second Intel 8259 PIC. The first PIC, the master, is the only one that directly signals the CPU. The second PIC, the slave, instead signals to the master on its IRQ 2 line, and the master passes the signal on to the CPU. There are therefore only 15 interrupt request lines available for hardware. The easiest way of viewing this information on Microsoft Windows
Microsoft Windows

Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces ....
 is to use Device Manager
Device Manager

File:Vista Device Manager.pngFile:Device Manger Windows 2003.pngThe Device Manager is a Control Panel applet in Microsoft Windows operating systems....
 or System Information (msinfo32.exe). On Linux
Linux

Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
, you can run "cat /proc/interrupts" or "procinfo".

Master PIC

  • IRQ 0 - System timer. Reserved for the system. Cannot be changed by a user.
  • IRQ 1 - Keyboard. Reserved for the system. Cannot be altered even if no keyboard is present or needed.
  • IRQ 2 - Cascaded signals from IRQs 8-15. A device configured to use IRQ 2 will actually be using IRQ 9
  • IRQ 3 - COM2 (Default) and COM4 (User) serial ports
  • IRQ 4 - COM1 (Default) and COM3 (User) serial ports
  • IRQ 5 - LPT2
    LPT

    LPT is the original, yet still common, name of the parallel port interface on PC compatible computers. It was designed to operate a text computer printer that used IBM's 8-bit extended ASCII character set....
     Parallel Port 2 or sound card
  • IRQ 6 - Floppy disk controller
    Floppy disk controller

    A floppy disk controller is a special-purpose chip and associated circuitry that directs and controls reading from and writing to a computer floppy disk ....
  • IRQ 7 - LPT1
    LPT

    LPT is the original, yet still common, name of the parallel port interface on PC compatible computers. It was designed to operate a text computer printer that used IBM's 8-bit extended ASCII character set....
     Parallel Port 1 or sound card (8-bit Sound Blaster and compatibles)


Slave PIC

  • IRQ 8 - Real-time clock
    Real-time clock

    A real-time clock is a computer clock that keeps track of the current time. Although the term often refers to the devices in personal computers, server s and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time....
     (RTC)
  • IRQ 9 - Free / Open interrupt / Available / SCSI. Any devices configured to use IRQ 2 will actually be using IRQ 9.
  • IRQ 10 - Free / Open interrupt / Available / SCSI
  • IRQ 11 - Free / Open interrupt / Available / SCSI
  • IRQ 12 - PS/2 connector
    PS/2 connector

    The PS/2 connector is used for connecting some Computer keyboard and computer mouse to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987....
     Mouse. If no PS/2 connector
    PS/2 connector

    The PS/2 connector is used for connecting some Computer keyboard and computer mouse to a PC compatible computer system. Its name comes from the IBM Personal System/2 series of personal computers, with which it was introduced in 1987....
     mouse is used, this can be used for other peripherals
  • IRQ 13 - ISA / Math co-processor
  • IRQ 14 - Primary IDE Channel
  • IRQ 15 - Secondary IDE Channel


More Information

More information on the Intel 8259 PIC and its IRQ lines can be found in the IA-32 Intel Architecture Software Developer’s Manual, Volume 3A: System Programming Guide, Part 1, freely available on the Intel website.


See also

  • Advanced Programmable Interrupt Controller
    Advanced Programmable Interrupt Controller

    An Advanced Programmable Interrupt Controller is a more intricate Programmable Interrupt Controller containing a magnitude more outputs, much more complex priority schema, and Advanced IRQ management....
  • Programmable Interrupt Controller
    Programmable Interrupt Controller

    A programmable interrupt controller is a device which allows priority levels to be assigned to its interrupt outputs. When the device has multiple interrupt outputs to assert, it will assert them in the order of their relative priority....
  • Intel 8259
    Intel 8259

    The Intel 8259 is a family of Programmable Interrupt Controllers designed and developed for use with the Intel 8085 and Intel 8086 8-bit and 16-bit microprocessors....
  • Interrupt handler
    Interrupt handler

    An interrupt handler, also known as an interrupt service routine , is a callback subroutine in an operating system or device driver whose execution is triggered by the reception of an interrupt....
  • Input/Output Base Address
    Input/Output Base Address

    In x86 architecture, an input/output base address is a base address used for an I/O port....
  • Plug-And-Play
    Plug-and-play

    In computing, plug and play is a term used to describe the characteristic of a computer bus, or device specification, which facilitates the discovery of a hardware component in a system, without the need for physical device configuration, or user intervention in resolving resource conflicts....
  • Polling
    Polling (computer science)

    Polling, or polled operation, in computer science, refers to actively sampling the status of an external device by a client program as a synchronous activity....