A computer can feel impossibly abstract until somebody shows where the ones and zeroes physically come from.
Visit Boston University’s From Transistors to Functions module
This old Boston University computer-science lesson starts low in the stack: a transistor has terminals, a control input and two useful states. From there it builds upward until those switches become logic gates and those gates become functions.
The page’s teaching trick is a faucet.
A transistor is compared to water controlled by a knob. Turn the gate on and current can flow. Turn it off and the path closes. Complementary CMOS transistors reverse that behavior, giving the two kinds of switches needed to construct digital logic efficiently.
It is simplified, but it gives beginners something physical to hold onto before the diagrams multiply.
Two transistors, then a computer
The lesson next connects transistors into an inverter, or NOT gate, and works through both possible inputs. A truth table reduces the circuit to its behavior: zero becomes one, one becomes zero.
Then come NAND and NOR.
The page does not simply present their symbols. It walks through which transistors are conducting for each input combination and derives the output. NAND can then feed a NOT gate to produce AND; NOR can feed a NOT gate to produce OR.
By the time the familiar logic symbols appear, the reader has already seen what they are hiding.
The module continues into larger functions and eventually constructs XOR from combinations of simpler gates. From there the conceptual ladder is clear: transistors make gates, gates make larger logic functions, and enough logic functions make the machinery inside a processor.
The page includes period markers almost accidentally. It refers to roughly one million transistors per square millimeter as circa 2006 technology and to an Intel processor with more than 1.5 billion transistors as circa 2007.
The underlying lesson is older still. The material says it was adapted from lecture notes by Azer Bestavros first developed for CS-101 in 1995.
That gives the page an interesting durability.
Processor counts have exploded. The fundamental bridge from switching devices to Boolean logic has not.
A modern course could rebuild the lesson with animations, interactive widgets and a JavaScript simulator. Those might help. But the old page already has the essential pieces: diagrams, truth tables, a patient sequence and enough explanation to make the abstraction collapse one layer at a time.
The Web is good at preserving tutorials whose examples become dated while their reasoning remains useful.
The transistor count changed.
NOT is still NOT.