Lesson 1 of 7 · about 8 min
A room full of light switches
Every computer is built from tiny on/off switches called bits. Each extra switch doubles what you can say.
Imagine you and a friend live across the street from each other. You can’t call or text, but you each have a lamp in your window.
You agree on a code: lamp on means “come over”, lamp off means “not now.”
That’s it. With one lamp you can send exactly two messages. It sounds tiny, but this is the whole secret of computers. A modern laptop is a room with billions of these tiny switches, flipping on and off billions of times a second.
Another way: a yes/no question
Think of a single yes/no question: “Is the door locked?” The answer is one of exactly two things. A computer stores every answer like that as one tiny switch. Everything a computer knows (photos, songs, this sentence) is a huge pile of yes/no answers.
Another way: a coin on a table
Put a coin on a table. It’s either heads or tails, nothing in between. One coin can remember one of two things. A computer’s memory is like billions of coins that can each be flipped in a few billionths of a second.
Another way: Morse code
Old telegraph operators sent whole books using only short and long beeps. Computers do the same with just two signals, on and off. Two is enough if you have enough of them.
But what if you want to say more than “come over” and “not now”? Add another lamp. That’s where it gets interesting.
How many messages can your lamps send?
Flip the switches and try to make every different pattern. Then add a switch and see what happens to the total.
Switches: 2
You’ve made 1 of 4 different patterns. Can you find them all?
- 00
Grown-up words for what you just did
Each switch is called a bit, short for “binary digit.” We write on as 1 and off as 0. Binary just means “made of two options.”
You probably noticed the rule: every switch you add doubles the number of patterns.
| Switches (bits) | Patterns | Why |
|---|---|---|
| 1 | 2 | on, off |
| 2 | 4 | 2 × 2 |
| 3 | 8 | 2 × 2 × 2 |
| 8 | 256 | 2 multiplied by itself 8 times |
Mathematicians write “2 multiplied by itself n times” as 2ⁿ (say “two to the n”). So n bits make 2ⁿ patterns. That doubling is why computers get so powerful so quickly: 64 bits make about 18 billion billion patterns.
One more important idea: a pattern means nothing on its own. 101 only means something because someone agreed on a code, like “on, off, on means pizza night.” The next two lessons are about the codes computers use for numbers and letters.
Use the doubling rule
A teacher wants to give each of 30 students their own unique lamp pattern. What's the smallest number of switches that works?
Think bigger
You have 10 switches. You add just ONE more. What happens to the number of patterns?
What is a bit?
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