Concepts explained
A Computer Knows Nothing At All
The computer showing you this page cannot read it. It knows exactly two things: on and off. And with those two things, it got this far.
Think of a light switch. On or off, one of the two. A computer is that switch, collected in enormous numbers.
How enormous? A chip the size of your fingernail holds tens of billions of them. More switches on your fingernail than there are people on Earth.
Switches that press switches
There is one decisive difference from the switch on your wall. A wall switch needs a human finger. The switches inside a computer are pressed by electricity.
One switch turns on, its current turns on the next, which turns on the next — dominoes. Switches turning each other on and off with no hand involved: that is the whole of what a computer does.
Building a switch that electricity could press was the great homework problem for decades. At first, actual bits of metal clacked back and forth: slow and noisy. Then came glass tubes like light bulbs: fast, but hot and forever burning out. Early computers filled a room and broke somewhere almost daily.
In the winter of 1947 a part like a tiny pebble took over the job. No moving parts, no heat to speak of, almost nothing to wear out. The transistor.
A little further in
But how do switches add up to 'calculating'?
Here is the strangest part. Change how a few switches are joined, and something like judgement appears.
Put two switches in one line and the lamp at the end lights only when both are on. It reacts only when both conditions hold — 'it is raining AND I have no umbrella'.
Put the two switches side by side and either one lights the lamp. This part answers to 'mother calls OR father calls'.
AND, OR, NOT. Those three wirings are the smallest parts of thought. Stack billions and you get addition; stack additions and you get multiplication; on top of that ride letters, pictures, sound.
The astonishing thing is the order of events. This fact arrived a century before the computer — on paper, not in a machine. A self-taught Irish mathematician showed that thinking has rules of calculation, and at the time it looked perfectly useless.
A hundred years later, the people puzzling over how to join their switches opened that old book again.
But a switch has only two states. How do you hold the world's numbers, letters and photographs in something that only has two of anything? The next piece starts there.
The question that remainsIf tens of billions of switches turning each other on and off is all there is, what exactly does 'the computer knows' mean?