IRQ: Meaning (information, definition, explanation, facts)

IRQ stands for interrupt request. IRQs are used by peripherals as a way to bring the processor into attention. In the early PC-architecture the chips 8259A and 8259B takes care of the requests and sends them to the processor in form of ordinary software interrupts.

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
• IRQ1 = keyboard
• IRQ2 = reserved for the 8259B
• IRQ3 = COM1 and COM3
• IRQ4 = COM2 and COM4
• IRQ5 = LPT
• IRQ6 = Floppy drives
• IRQ7 = LPT
• IRQ8 = Real-time clock (RTC)
• IRQ9 = Video card
• IRQ10 - 12 = reserved
• IRQ13 = Math coprocessor
• IRQ14 = Primary IDE drives
• IRQ15 = Secondary IDE drives