1. Introduction

2. The Machine

   A computer is built from one part repeated: a switch that is either on or off, a scrap of doped silicon that conducts only when told to. These chapters stack that switch into logic, logic into arithmetic and memory, and all of it into a processor that runs a program held in its own memory, then ask how a machine that large is described, made faster by overlap, caching, and many cores at once, and even configured after it is built.

   1. How does sand become a switch?
   2. What can gates do?
   3. How does it add?
   4. How does it remember?
   5. What is a CPU?
   6. How is a circuit described?
   7. How does a CPU go faster?
   8. How does a CPU hide slow memory?
   9. What if one core is not enough?
   10. How can one chip become any circuit?

3. The Software

   A bare processor understands only numbers. These chapters give it language: an assembler that turns names into those numbers, a lexer and a compiler that turn human-written programs into them, and an operating system that runs many programs at once and hands each one memory, files, and a way to ask the machine for help.

   1. How is code turned to bits?
   2. How do programs combine?
   3. How does text become tokens?
   4. How do programs run programs?
   5. What is a language?
   6. How does a loop become jumps?
   7. Who is in charge?
   8. How does a program ask for help?
   9. Where does new memory come from?
   10. How does each program get its own memory?
   11. How are files stored?
   12. How does a program get loaded and run?

4. The Network

   So far each machine has run alone. These chapters connect them: a single bit driven across a wire, framed into bytes, addressed to a neighbour, routed across many machines, made reliable, given meaning, and at last made private, so two strangers anywhere can hold a conversation no one else can read.

   1. How do bits cross a wire?
   2. How do you send a bit by hand?
   3. Who has this address?
   4. How do they find each other?
   5. How is it reliable?
   6. How do they speak?
   7. How do two strangers share a secret?

5. The Browser

   Everything beneath now exists: a machine, its software, and a network between machines. These last chapters spend it all on a single act, opening a web page, following it from the name you type down through every layer and back up to the pixels on the screen.

   1. What happens when I open a URL?
   2. How does a page become pixels?
   3. The whole machine