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Floppy drive controller
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LPT1
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Sound card
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Com1
EXPLANATION
IRQs ((Interrupt Request Line) are hardware lines over which devices can
send interrupt signals to the microprocessor. When you add a new device
to a PC, you sometimes need to set itsIRQ number by setting a DIP
switch. This specifies which interrupt line the device may use.
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.
IRQ
0System timerThis interrupt is reserved for the internal system timer.
It is never available to peripherals or other devices.IRQ 1
KeyboardThis 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 8-15This 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 cardThis interrupt is the first choice that most sound cards make when looking for an IRQ setting.
IRQ 6 Floppy disk controllerThis interrupt is reserved for the floppy disk controller.
IRQ
7 First parallel portThis 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
clockThis interrupt is reserved for the system's real-time clock timer
and can not be used for any other purpose.
IRQ 9 Open interruptThis interrupt is typically left open on devices for the use of peripherals.
IRQ 10 Open interruptThis interrupt is typically left open on devices for the use of peripherals.
IRQ 11 Open interruptThis interrupt is typically left open on devices for the use of peripherals.
IRQ
12 PS/2 mouseThis 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/coprocessorThis 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
channelThis 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 channelThis interrupt is reserved for use by the secondary IDE controller.
SOURCE
