Code by Charles Petzold starts with a flashlight and ends with a computer

You can write software for years without really knowing what happens underneath. This book fixes that, slowly and kindly. It starts with two kids signalling with flashlights, moves on to Morse code and relays, and step by step you end up with something that can run a program.

No chapter feels hard on its own, which is the clever part. Somewhere around the memory chapters I realised I finally understood something I'd been nodding along to for ages. It's a great one to give to someone curious about computers, even if they never plan to code.