How computers think: binary, transistors & you
A sit-together course for a sharp six-year-old. Real computer science ideas, explained with light switches, games, and tiny electric brains.
Uncle / Teacher guide
- Sit side by side. Let him click the bits and buttons.
- Do one lesson per sitting if focus runs out — stopping is fine.
- Hands-on extras: a real light switch, paper & pencil, flashlight.
- Goal: he can explain “computers only use ON and OFF” in his own words.
- Yellow boxes = activities. Purple boxes = tips for you.
Course map
Three big ideas that stack on each other.
Binary: the secret code
Only two digits — 0 and 1. Learn to count and “read” computer language.
Transistors: tiny switches
How electricity becomes decisions. Logic gates you can play with.
From switches to computers
Memory, chips, and how billions of switches run games and phones.
Binary — the secret code of computers
Everything a computer “knows” is built from just two signals.
ON and OFF is enough
You (decimal)
Digits: 0 1 2 3 4 5 6 7 8 9
Base 10 — ten choices per place
Computer (binary)
Digits: 0 and 1 only
Base 2 — two choices per place
A single binary digit is called a bit (binary digit). One bit can only mean 0 or 1. With more bits, you can make bigger numbers — and letters, pictures, and games.
Click the bits — make a number
Each bit has a place value, like hundreds/tens/ones — but powers of 2: 8, 4, 2, 1.
Tip: turn on the 8-bit and the 1-bit → 8 + 1 = 9. Binary looks like 1001.
Count from 0 to 15 (4 bits)
| Binary | Normal | How to think about it |
|---|---|---|
| 0000 | 0 | All off |
| 0001 | 1 | Just the 1 |
| 0010 | 2 | Just the 2 |
| 0011 | 3 | 2 + 1 |
| 0100 | 4 | Just the 4 |
| 0101 | 5 | 4 + 1 |
| 0110 | 6 | 4 + 2 |
| 0111 | 7 | 4 + 2 + 1 |
| 1000 | 8 | Just the 8 |
| 1001 | 9 | 8 + 1 |
| 1010 | 10 | 8 + 2 |
| 1111 | 15 | 8 + 4 + 2 + 1 — max for 4 bits! |
Letters are numbers too
Computers store letters as numbers using a code called ASCII (and similar codes). Each letter has a number, and that number is stored in binary.
You don’t need to memorize these — just know: text, pictures, and sound are all long lists of 0s and 1s underneath.
Decode challenge
Type a 4-bit binary number (like 1010) and decode it:
🖐️ Hands-on activity: Finger binary
Use four fingers on one hand as bits (thumb = 8, index = 4, middle = 2, ring = 1). Up = 1, down = 0. Race: who can show the number 11 first? (Answer: 1011 — thumb, middle, ring up; index down… or 8+2+1.)
Optional: write a secret number in binary on paper and have him decode it.
Transistors — tiny electric switches
Binary needs something physical that can be ON or OFF. That something is the transistor.
Start with a normal switch
Light switch model
OFF · no electricity path
Same idea, computer style
When the path is open, we call that bit 1. When closed/blocked, we call it 0.
(controlled by the switch on the left)
What’s special about a transistor?
Wall switch
Your finger moves a piece of metal. Good for lights. Too big and slow for a computer brain.
Transistor
No finger. Electricity controls electricity. Billions fit on a chip the size of a fingernail. Flip millions of times per second.
Three legs (simple model)
Many transistors have three connections. Think of them like this:
The base is the decision maker.
Small “yes” at the base → path opens → current can flow (bit 1).
“No” at the base → path stays closed (bit 0).
Real transistors have more physics (fields, semiconductors, NPN/PNP types). For this age, “electricity-controlled switch” is the truth that matters.
Logic gates — transistors making decisions
Wire transistors together and you get logic gates: tiny rule machines. Computers are oceans of these rules stacked into math, memory, and graphics.
NOT Flip it
Output is the opposite of the input. 1 becomes 0; 0 becomes 1.
AND Both must agree
Output is 1 only if both inputs are 1. Like needing two keys.
OR Either works
Output is 1 if either input is 1 (or both). Like two doorbells.
🖐️ Hands-on activity: Human logic gates
Two people are inputs (arms up = 1, down = 0). A third person is the gate. For AND: only raise a flag if both arms are up. For OR: raise if either is up. For NOT: do the opposite of one person. Act it out — it sticks.
From switches to modern computers
How billions of 0s and 1s become games, videos, and messages.
How big is “billions”?
A single human hair is about 100,000 nanometers wide. The switches on a chip are only a handful of nanometers across — so small you need special microscopes. That’s why phones can be powerful and fit in a pocket.
The chain from switch to “fun”
1. Transistor
Electric switch: ON (1) or OFF (0).
2. Logic gates
AND, OR, NOT (and friends) decide new bits from old bits.
3. Circuits for math & memory
Adders do arithmetic. Memory cells store bits until you need them again.
4. Chips (integrated circuits)
Millions/billions of transistors printed onto silicon — the “brains” of devices.
5. Computer / phone / console
CPU + memory + storage + screen. Software sends instructions; hardware flips switches to obey.
Memory: remembering bits
RAM (short-term)
Fast memory for what you’re doing right now — open game, open tab. Needs power. Like a whiteboard.
Storage (long-term)
SSD/hard drive keeps files when the power is off. Like a notebook on a shelf.
Both store binary. A photo is millions of numbers for color dots (pixels). A song is millions of numbers for air pressure over time. Same alphabet: 0 and 1.
CPU: the boss of instructions
The CPU (Central Processing Unit) fetches instructions, decodes them, and executes them — add these numbers, compare those bits, jump to a different instruction, draw this pixel. Every step is ultimately transistors changing 0s and 1s extremely fast.
Why this matters for “modern computing”
Reliable simplicity
Two states are robust. You can pack more switches, run them faster, and still tell 0 from 1.
Universal machine
Same hardware idea runs calculators, rockets, Minecraft, and hospital scanners — different software, same binary foundation.
Moore’s Law (story form)
For decades, engineers roughly doubled transistor counts on chips over time. Computers got smaller, cheaper, stronger.
You can learn more layers
Next steps later: electricity basics, simple circuits, block coding, then real programming — all sit on this foundation.
🖐️ Hands-on activity: Device scavenger hunt
Walk around the house. Point at things that almost certainly use transistors: phone, TV remote, microwave panel, car key fob, game controller, Wi‑Fi router, smart lights. Bonus question: “Is a bicycle computer-ish?” (Usually no transistors — pure mechanical.)
Boss battle quiz
No grades — just see what stuck. Talk through wrong answers together.
1. How many different digits does binary use?
2. What is a bit?
3. Binary 0101 equals which normal number? (places: 8 4 2 1)
4. A transistor is best described as…
5. An AND gate outputs 1 when…
6. Why do computers use binary instead of counting like humans?
Junior Binary Engineer
This certifies that
can explain binary (0 and 1), knows transistors are tiny switches, and understands how those switches help computers think.
Parent / uncle cheat sheet
Print this page section or keep it open while teaching.
Key vocabulary
Bit — one 0 or 1
Binary — base-2 number system
Transistor — tiny electric switch
Logic gate — rule built from transistors
CPU — chip that runs instructions
RAM — fast short-term memory
Suggested schedule
Day 1: Lesson 1 + finger binary
Day 2: Lesson 2 + human gates
Day 3: Lesson 3 + scavenger hunt + quiz
Anytime: Revisit clickable demos
If he wants more later
LED + battery + switch kit · Scratch / block coding · “Code.org” courses · simple Arduino with adult help · books on how computers work with cutaway drawings
Accuracy notes (for you)
We simplified semiconductors, CMOS pairs, and ASCII vs Unicode. That’s intentional. The model “binary → transistors → logic → chips → software” is correct and age-appropriate.