Prior to plug and play devices, users had to set IRQ values of devices manually when adding the device, such as a modem or printer, to a system. The following list of IRQ numbers specifies what each of the 16 IRQ lines are used for.
Prior to plug-and-play devices, users had to set IRQ values of devices manually when adding the device, such as a modem or printer, to a system. The following list of IRQ numbers specifies what each of the 16 IRQ lines are used for.
| RQ Number |
Typical Use |
Description |
| IRQ 0 |
System timer |
This interrupt is reserved for the internal system timer. It is never available to peripherals or other devices. |
| IRQ 1 |
Keyboard |
This interrupt is reserved for the keyboard controller. Even on devices without a keyboard, this interrupt is exclusively for keyboard input. |
| IRQ 2 |
Cascade interrupt for IRQs 8-15 |
This interrupt cascades the second interrupt controller to the first. |
| IRQ 3 |
Second serial port (COM2) |
The interrupt for the second serial port and often the default interrupt for the fourth serial port (COM4). |
| IRQ 4 |
First serial port (COM1) |
This interrupt is normally used for the first serial port. On devices that do not use a PS/2 mouse, this interrupt is almost always used by the serial mouse. This is also the default interrupt for the third serial port (COM3). |
| IRQ 5 |
Sound card |
This interrupt is the first choice that most sound cards make when looking for an IRQ setting. |
| IRQ 6 |
Floppy disk controller |
This interrupt is reserved for the floppy disk controller. |
| IRQ 7 |
First parallel port |
This interrupt is normally reserved for the use of the printer. If a printer is not being used, this interrupt can be used for other devices that use parallel ports. |
| IRQ 8 |
Real-time clock |
This interrupt is reserved for the system’s real-time clock timer and can not be used for any other purpose. |
| IRQ 9 |
Open interrupt |
This interrupt is typically left open on devices for the use of peripherals. |
| IRQ 10 |
Open interrupt |
This interrupt is typically left open on devices for the use of peripherals. |
| IRQ 11 |
Open interrupt |
This interrupt is typically left open on devices for the use of peripherals. |
| IRQ 12 |
PS/2 mouse |
This interrupt is reserved for the PS/2 mouse on machines that use one. If a PS/2 mouse is not used, the interrupt can be used for other peripherals, such as network card. |
| IRQ 13 |
Floating point unit/coprocessor |
This interrupt is reserved for the integrated floating point unit. It is never available to peripherals or other devices as it is used exclusively for internal signaling. |
| IRQ 14 |
Primary IDE channel |
This interrupt is reserved for use by the primary IDE controller. On systems that do not use IDE devices, the IRQ can be used for another purpose. |
| IRQ 15 |
Secondary IDE channel |
This interrupt is reserved for use by the secondary IDE controller. |
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This article was originally published on June 24, 2010
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