From Sand to CPU
Build a CPU from first principles
Level 0
Sand to Silicon
Where it all begins
Analogy · Silicon is sand that learned to switch. The rest of this course is building bigger things out of billions of those switches.
Silicon is a : a material that sits between conductors (like copper) and insulators (like glass). On its own it barely conducts — but apply a small to the right place and it suddenly becomes a wire. That third terminal is the trick that makes everything else possible.
pure silicon with phosphorus (N-type, electron donors) or boron (P-type, electron acceptors) creates regions that conduct only under specific voltage conditions. Sandwich them N-P-N or P-N-P and you get a .
A transistor has three terminals: source, drain, and gate. Apply enough voltage to the gate and current flows from source to drain. Drop the voltage and it stops. A switch with no moving parts, operable in nanoseconds, with no wear-out mechanism.
A modern CPU has roughly 10–100 billion transistors on a chip the size of a fingernail. They switch billions of times per second. The next 11 levels build up from a single transistor-worth of decision-making to a full CPU, one layer at a time.
First working transistor: Bardeen, Brattain & Shockley, Bell Labs, December 1947. They shared the 1956 Nobel Prize in Physics for it.