Silence on the Wire

I/O Entropy: This Is Your Mouse Speaking

On almost every computer system, external devices communicate relevant asynchronous events, such information being made available from the network card or the keyboard, using a hardware interrupt mechanism. Each device has an assigned hardware interrupt (IRQ) number and reports important developments by changing the voltage on a designated hardware line inside the computer, corresponding to this particular IRQ. The change is then interpreted by a device called a programmable interrupt controller (PIC), which serves as a personal butler for the main processor (or processors).

Once instructed by the CPU, the PIC decides if, when, how, and with what priority to deliver requests from the external devices to ...