These pages are the clean statement of an idea you have already met — usually in an exploration, a warm-up, or something that went wrong on your screen. The order below is the order the course needs them in, not the order they appear in a textbook. Come here after class, when you want the idea in one place and in plain words.

Unit 1 — Programs that decide, and the machine that runs them

Unit 2 — Repetition, data, and what computing costs

Unit 3 — Structure, files, and design

Unit 4 — Building for someone else