Computer and Software Support


IRQ definition 

Below is a list of the IRQ numbers on the system 

IRQ Number
Typical Use
Description
IRQ 0 System timer This is reserved for the internal system timer. This is not available to peripherals or other devices.
IRQ 1 Keyboard Reserved for the keyboard controller. 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.