A Transistor Is Just a Switch

The board draws the ladder built on top of this idea: switch to gate to arithmetic to a whole CPU, the way Logic From Switches (transistors → gates → adder → memory) climbs it. This lesson goes the other way, down into one rung of that ladder, into what a transistor is actually doing when it looks like it is switching.

Before you start. You need to know that electricity is just a crowd of electrons moving through a wire, and that a computer stores everything as one of two states, on or off. That’s the whole background this lesson assumes.