How Computers Actually Work
Under the screen: how a machine that only knows 'on' and 'off' can run games, videos, and everything else.
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Big Idea
How Computing Works
Grade bands
K-2 · 3-5 · 6-8 · 9-12
AI literacy pillar
How AI works · Ethics
Lesson overview
Under the screen: how a machine that only knows 'on' and 'off' can run games, videos, and everything else. This module climbs from an everyday intuition to the real mechanism, then names the Stanford course it descends from.
Teacher script · ~45 min
- 0–5
Hook
Deep down a computer has millions of tiny switches, each either ON or OFF. That's it. We call one switch a BIT. Group switches together and patterns of on/off can stand for a number, a letter, a color, a sound. A computer is astonishing not because each part is clever, but because it flips simple switches billions of times a second.
- 5–15
Explore
Students do the activity in pairs: Number ten cups 0–9, put a number in each, and be the CPU: 'read cup 3, add cup 4, write it in cup 5.' You just executed instructions against memory.
- 15–30
Explain
The magic is LAYERS. Bits form numbers; numbers form instructions; instructions form programs; programs stack into the operating system and then the apps you touch. Each layer hides the messy one beneath it, so an app developer never thinks about switches. This idea — ABSTRACTION, building reliable layers on top of simpler ones — is the single biggest idea in all of computing.
- 30–40
Connect to the summit
Show students this is the real thing professionals build: The real systems stack. Under the screen: how a machine that only knows 'on' and 'off' can run games, videos, and everything else.
- 40–45
Check
Run the formative check below. Anyone who can explain a key term in their own words has it.
Student activity
Number ten cups 0–9, put a number in each, and be the CPU: 'read cup 3, add cup 4, write it in cup 5.' You just executed instructions against memory.
Slides
Formative check
- 1.In your own words, what is "Bit"? (Looking for: A single on/off switch — the smallest piece of information a computer has.)
- 2.In your own words, what is "Memory"? (Looking for: A wall of numbered boxes the computer reads from and writes to.)
- 3.In your own words, what is "Processor (CPU)"? (Looking for: The fast worker that follows simple instructions one after another.)
Carry-away concepts
- Bit
- A single on/off switch — the smallest piece of information a computer has.
- Memory
- A wall of numbered boxes the computer reads from and writes to.
- Processor (CPU)
- The fast worker that follows simple instructions one after another.
- Abstraction
- Hiding a complicated layer behind a simple one you can use without knowing the details.
From the summit · the Stanford source
A working mental model of a computer from the ground up — bits, memory, processor, and software — so nothing on your device is magic anymore.
This module descends from CS1H at Stanford. Students who climb the full ladder arrive here.