IRQ

An IRQ or interrupt request is the means by which hardware components request computing time from the central processing unit.

=IRQs for IBM PC compatible computers=

The modern IBM PC compatible computer has 16 IRQ assignments (0-15), each one representing a different physical (or virtual) piece of hardware. For example, IRQ0 is reserved for the system timer, while IRQ1 is reserved for the keyboard. The lower the number, the more critical the function.

In the past, there were only 8 IRQ assignments (0-7). As the need for more hardware emerged, the need for more IRQs arose. The solution was another 8 IRQs, added by bridging IRQ2 to the new IRQ9.

In Pentium-class (and some 80486-class) computers the IRQs can be handled by the APIC.

The list of IRQs is:

IRQ0 = 8253/8254 interval timer (system timer)

IRQ1 = Computer keyboard

IRQ2 = reserved for the 8259B (tied to IRQ 9)

IRQ3 = COM2 and COM4

IRQ4 = COM1 and COM3

IRQ5 = LPT2 or sound card

IRQ6 = floppy drives

IRQ7 = LPT1

IRQ8 = real-time clock (RTC)

IRQ9 = bridged to IRQ2

IRQ10 = not assigned

IRQ11 = not assigned

IRQ12 = PS/2 computer mouse

IRQ13 = math coprocessor

IRQ14 = Primary Advanced Technology Attachment drives

IRQ15 = Secondary Advanced Technology Attachment drives

=See also=

I/O address

Input/Output Base Address

=External links=

*[http://www.pcnineoneone.com/howto/irq1.html Understanding IRQs] *[http://www.duxcw.com/faq/irq/irq.htm Interrupt Requests]