What Is a Computer Chip, Anyway?

Chapter 1: What Is a Computer Chip, Anyway?

The Day Mia Broke the World Open

The tablet slipped out of Mia's hands at exactly 4:17 p.m. on a Tuesday.

It happened the way these things always happen: she was reaching for a cookie, leaning over the kitchen counter, and the tablet was balanced on the very edge, where she had left it while watching a video about baby otters. One second it was there. The next second, it was not. Mia heard the *thunk* of plastic on tile, then the *crack* of glass giving up, and then her mother's voice from the other room: "Mia? What was that?"

"I'm fine!" Mia said quickly. She picked up the tablet. The screen had a spiderweb crack across one corner, but the rest of it was still glowing. The baby otters were still floating on a raft. A tiny speaker was still playing a happy little song.

Mia stared at the cracked corner. She could see *into* the tablet now, just a little. A thin, dark sliver inside the gap, no bigger than a grain of rice, was shining faintly in the light. "Mom," she said slowly. "What's *in* here?"

Her mother came over, looked at the crack, and shrugged. "Lots of tiny things," she said. "Little computers. Little brains."

"But *what* are they?"

Her mother smiled. "That's a really good question. And it has a really cool answer."

That night, after the tablet had been carefully wrapped up and put in a drawer, Mia lay in bed and thought about that shining grain-of-rice thing inside the crack. *What is in there? How does it think? Why did the otter video still play even though the screen was broken?*

If you have ever dropped something, broken it open, or asked a question that nobody answered properly — you are already thinking like Mia. And you have just asked the exact question this chapter is going to answer.

So: what is a computer chip, anyway?

A Chip Is a Tiny Slice of Sand That Thinks

Let's start with the word *chip*. A chip — in the way we mean it in this book — is a very small, very flat, very thin piece of material, usually a mineral called silicon, that has been decorated with an almost unbelievable number of even tinier *things* on its surface. Those tiny things are called transistors, and we are going to spend a lot of time with them, because transistors are the secret heroes of *every single* digital device you have ever used.

A chip is so small that you can hold one on the tip of your finger. The biggest chips, the kind that power big computers and game consoles, are roughly the size of a postage stamp. Many of the chips inside your phone or your tablet are smaller than your smallest fingernail. Some are so small that you would need a magnifying glass, or a microscope, just to see one at all.

But here is the mind-bending part: that tiny piece of silicon can hold billions of transistors. Not a hundred. Not a thousand. *Billions.* A modern smartphone chip can have more than 100,000,000,000 transistors packed onto a surface smaller than a fingernail. If you tried to count them out loud, one number per second, it would take you more than 3,000 years to finish.

So the first thing to remember is this: a chip is a tiny slice of silicon filled with billions of transistors. Say it to yourself. Say it out loud. Tiny slice. Silicon. Billions of transistors. That is your seed, and we are going to grow it into a giant tree of understanding by the end of this chapter.

But where does silicon come from?

Silicon is one of the most common substances on Earth. You probably walked over a pile of it today without knowing. Sand is mostly silicon. So are many rocks. So is a large part of the Earth's crust. The sand on a beach and the chip in a phone are distant cousins — they are made of the same stuff. The difference is that the silicon in a chip has been purified and polished and carved into one of the most perfect surfaces ever made by humans.

Imagine taking a beach, melting it down, filtering out everything that is not silicon, removing every tiny impurity, every speck of dust, every stray atom of something else, and then letting the silicon cool into a perfect, glowing cylinder. That cylinder is called an ingot. It is shiny, gray, and heavy. It looks a bit like a giant metal sausage. Then the ingot is sliced, with a special saw, into wafers — paper-thin discs that look like record albums made of mirror. Each wafer will eventually be cut up into dozens or even hundreds of individual chips.

So a chip really is sand. Just sand that has been taught to think.

The Tiniest Switches in the World

Now we get to the heart of the matter: the transistor.

A transistor is the smallest working part inside a chip. It is so small that you cannot see it with your eyes, and even with a regular microscope, you would have a hard time. To see one transistor clearly, you would need an electron microscope, which uses tiny beams of electrons (not light) to draw a picture of things that are too small for light to see.

But here's the trick: you don't need to *see* a transistor to understand what it does. You only need to imagine a light switch.

You have a light switch in your room, right? It has two positions: ON and OFF. When the switch is ON, electricity flows through the wires, and the light turns on. When the switch is OFF, the electricity stops, and the light turns off. That's all a light switch does. It has only two choices. On, or off. Yes, or no. Go, or stop.

A transistor is a tiny, tiny version of a light switch. It can also be ON or OFF. When it's ON, electricity flows through it. When it's OFF, electricity doesn't flow. And that's the entire trick.

"But wait," you might say. "If a transistor can only be on or off, how does it do anything *interesting*? My light switch doesn't write poems or play baby-otter videos."

Excellent question. The answer is: one transistor can't do anything interesting by itself. Just like one letter of the alphabet can't write a story. But a *lot* of transistors, working together in clever patterns, can do basically anything a computer can do. The magic isn't in any one switch. The magic is in the teamwork.

ON means 1. OFF means 0.

Here's a secret code that the entire digital world uses. When a transistor is ON, we say it represents the number 1. When it is OFF, we say it represents the number 0. That's it. The whole language of computers is made of just two symbols: 1 and 0.

We call this language binary (pronounced "BY-neh-ree"). The word "binary" just means "having two parts." Binary is the alphabet that computers use. Just like English uses 26 letters to make every word in every book, computers use 2 symbols — 1 and 0 — to make every picture, every song, every game, every text message, every web page, and every video of baby otters ever made.

You can try this right now. Pretend I'm a computer. I can only understand two letters: 1 and 0. If I want to say "Hi," I have to write it like this: `01001000 01101001`. That looks like nonsense, but to a computer, it is exactly the same thing as the word "Hi." It is just spelled in a different alphabet.

Every photo on your phone, every song in your earbuds, every game you play, every video you watch — all of it, *all* of it, is stored as long, long, long strings of 1s and 0s. And every single one of those 1s and 0s is just a tiny transistor that is ON or OFF.

A picture of a baby otter? Probably more than ten million 1s and 0s. A whole movie? Trillions.

This is one of those ideas that is so simple it almost feels like a trick. But it is not a trick. It is the foundation of every digital thing you have ever used. From here on, whenever you see something amazing a computer can do, you can whisper to yourself: *that's just a lot of switches being on or off, very fast, in clever patterns.*

Ants, LEGOs, Pizza, and Tiny Cities

We have used the word "tiny" a lot. Let's stop and get a real feel for how tiny we are talking, because it is the kind of sm