Not a cloud. Not one giant computer in a building. A network of networks, owned by thousands of different organizations, held together by nothing but agreements about how to talk.
Ten minutes. Read it before class; we start from it. Enrolled in our Runestone course? Open it from there so your progress counts.
Internet lights up today. You’ve built bits (Unit 1), programs (Units 2–4), and data (Unit 5). This unit answers the question Lesson 0.1 asked on Day 1: how did that photo actually get there?
Most drawings have a cloud in them. By 6.15 yours won’t.
The internet is a computer network made of other computer networks: your home Wi-Fi, the school’s network, your internet provider’s network, phone carriers, cloud companies, universities. Each piece is owned and run by someone different. Nobody owns the whole thing, and nobody is in charge of it — and it was designed that way on purpose.
What holds it together is agreement. Every network that joins agrees to the same rules for sending data (those rules are 6.2’s topic). Follow the rules and you can connect; no permission from a central boss required.
Four words the AP exam uses precisely:
| Term | What it means | Example |
|---|---|---|
| computing device | a physical thing that can run a program | phone, laptop, server, router, smart thermostat |
| computing system | devices and programs working together for a purpose | a school’s attendance system |
| computer network | connected devices that can send and receive data | your home Wi-Fi |
| path | the chain of directly connected devices from sender to receiver | phone → router → … → grandma’s phone |
You send a photo from Irvine to your grandma in Manila. Press Next hop and watch who owns each piece of the path.
The path here is simplified — a real one usually has more routers in the middle — but the shape is right: many owners, several kinds of wire and radio, and no single company in charge.
Five questions. The words matter — read the stem twice.
Because joining only requires following the open rules, anyone can build a network and connect it — a school, a startup, a small country. That openness is why the internet grew so fast. The flip side: when something goes wrong, there’s no single office to call.