IRQ
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IRQs (or interrupt requests) are the means by which hardware components request computing time from the CPU. Today, there are 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 I/O APIC.
IRQs in the PC AT environment
- IRQ0 = 8253/8254 interval timer (System Timer)
- IRQ1 = keyboard
- IRQ2 = reserved for the 8259B (Tied to IRQ 9)
- IRQ3 = COM2 and COM4
- IRQ4 = COM1 and COM3
- IRQ5 = LPT2 or Soundcard
- IRQ6 = Floppy drives
- IRQ7 = LPT1
- IRQ8 = Real-time clock (RTC)
- IRQ9 = Bridged to IRQ2
- IRQ10 = Not Assigned
- IRQ11 = Not Assigned
- IRQ12 = PS/2 Mouse
- IRQ13 = Math coprocessor
- IRQ14 = Primary IDE drives
- IRQ15 = Secondary IDE drives
See also
External link
- Understanding IRQs (http://www.pcnineoneone.com/howto/irq1.html)
- Interrupt Requests (http://www.duxcw.com/faq/irq/irq.htm)