An IRQ, short for Interrupt Request, is used in a computer to send just that: a request for the CPU to be interrupted by another piece of hardware.

An Interrupt Request is needed for things like keyboard presses, mouse movements, printer actions, and more. When the request is made by a device to temporarily stop the processor, the computer can then give the device some time to perform its own operation.

For example, every time you press a key on the keyboard, an interrupt handler tells the processor to stop whatever it was doing so that the keystrokes can be processed.

Each device communicates its request over a unique data line, called a channel. You will usually see IRQ listed next to this channel number, also called the IRQ number. For example, IRQ 4 might be used for one device and IRQ 7 for another.