I/O, Interrupts & the Bus

A device ringing for the CPU’s attention instead of being checked on, and the shared wiring that carries the answer.

Before you start. You already know a CPU can be structured to juggle many tasks at once without finishing any of them first - that’s concurrency, and it’s what lets one core serve a busy server instead of handling one thing start-to-finish (Concurrency & the Hardware). This lesson is about the one event that makes that possible: the moment a slow device actually has something ready. If a network connection is new, TCP vs UDP, and the 3-way handshake in Networking shows it in one read.