You are looking at light

01 The atom

One atom of silicon

Fourteen protons and fourteen neutrons, wrapped in fourteen electrons arranged in shells of 2 · 8 · 4. The four outer ones — the valence electrons — are the whole story: each silicon atom wants to share them with four neighbours.

• 14electrons
• 2·8·4shells
• ~28%of Earth’s crust

02 The crystal

Four hands, a perfect crystal

Each atom shares its four with four neighbours, and the pattern repeats in every direction. Every electron is locked in a bond, so pure silicon barely conducts. Swap in phosphorus and one electron roams free: n‑type. Boron leaves a hole that drifts like a positive charge: p‑type.

• 0.543 nmone repeating cell
• 99.9999999%chip-grade purity

03 The switch

A switch with no moving parts

Two n‑type islands, source and drain, sit in p‑type silicon. Above the gap, behind a thin insulator, sits a gate. Gate off: no path, no current — 0. Gate on: its field pulls electrons into a thin channel and current flows — 1.

• a few nma few dozen atoms
• billionsof flips a second
• 10¹⁰+on one chip

04 Logic

Switches that decide

Wire four transistors together and you get NAND: its output is 0 only when both inputs are 1. NAND is universal — NOT, AND, OR and XOR can all be built from it, and so can every computer. Four NANDs make an XOR.

05 Arithmetic

Counting with two fingers

With only two states, you count in base 2: 0, 1, 10, 11, 100… A half adder is an XOR for the sum and an AND for the carry. Chain four full adders and watch the carries ripple left: five plus three.

• 0101 + 0011= 1000
• 5 + 3= 8

06 Memory

A loop that remembers

Feed two NOT gates into each other and the signal chases its own tail: a latch. It holds a 1 or a 0 for as long as the power stays on. An SRAM cell uses six transistors; main memory uses one transistor and a leaky capacitor, refreshed every ~64 ms.

• 6transistors per SRAM bit
• 01000001the letter ‘A’

07 The processor

Fetch, decode, execute

A clock ticks billions of times a second. On every tick the processor fetches an instruction — just a number — decodes it, executes it in the ALU and writes the result to a register. Then again.

• 3–5 GHzclock
• ~10 cmhow far light gets in one tick at 3 GHz

08 The chip

Printed with light

The patterns are printed onto a silicon wafer with extreme-ultraviolet light. Dozens of layers: transistors at the bottom, up to ~15 layers of copper wiring above. The die is cut, packaged and soldered to a board beside memory and power.

• 13.5 nmEUV light
• severalcores in your device, working now

09 Software

Numbers that mean something

Instructions are just bytes. People write languages; compilers turn them into machine code. The operating system shares the processor between hundreds of programs, thousands of times a second. One of them is your browser, on your computer — and it has an address to open.

• this pagethe address you opened

10 The network

Out through glass

DNS turns a name into an address. TCP shakes hands: SYN, SYN‑ACK, ACK. Then data travels in packets of ~1,500 bytes — voltage in copper, radio in Wi‑Fi, light in glass at ~200,000 km/s. Nearly all traffic between continents runs through undersea cables.

• …DNS lookup, this page
• …TCP handshake, this page

11 The server

The server answers

Your browser asked: GET / HTTP/1.1. The server replied 200 OK — and these are the real first bytes of this page, first as numbers, then as text.

• …until the first byte
• …bytes of HTML

12 The browser

Text becomes a tree, then pixels

The browser parses the HTML into a tree — hundreds of elements on this page — works out where every box goes (layout), what colour every pixel is (paint), and stacks the layers on the GPU (composite). Then it does it again, up to 120 times a second.

• –frames per second, now
• …until the first pixels

13 Pixels

And back to the start

Your screen: millions of pixels, each three tiny lights — red, green, blue — millions in all, each switched by its own transistor. A transistor is silicon. And silicon is…

• …pixels
• …tiny lights