Concepts explained
What Happens in One Click
Tap the screen and the app appears — a tenth of a second, less than a yawn. Inside it, the computer works through hundreds of millions of orders, one at a time, in sequence. Everything that looks simultaneous is an illusion.
Follow those steps. The moment your finger meets the glass, a grid beneath it notices the electrical change at that spot. The touch becomes a number at once — which row, which column. Just as piece two said: the world is swapped for numbers the instant it enters.
That number arrives, and a waiting bundle of orders (piece four's rule table) wakes. The processor reads them one at a time: fetch this number, add it to that, put the result there. Hundreds of millions of times.
At the end, for each of the screen's millions of dots, a number saying 'you are this colour' is computed and delivered. Only then does the app look, to us, like it has 'appeared'.
What 'at the same time' really is
Music plays while a message arrives and the map scrolls. The computer seems to be doing several things at once.
A clock sets the beat of this sprint, ticking billions of times a second, one order per tick. The 'gigahertz' in the adverts is the tempo: one gigahertz is a billion beats a second.
The processor's sense of time
To feel that speed, trade places. Let one beat of the processor be one human second.
within arm's reach — one second
a few seconds to a dozen
a trip of several minutes
a journey of days
a voyage of years
So the processor never waits. While a number is fetched from the bookshelf it changes jobs, and during a library trip it clears dozens of tasks. Most moments when a computer feels slow, it is not calculating slowly — it is waiting for something.
A little further in
How it all arrives unbroken
But is it not strange? Hundreds of millions of steps, errands to the shelf, the library, across the sea — and the numbers never spoil on the way? Electricity wobbles; radio carries noise.
In 1948 a mathematician faced this head-on. First he gave information a unit: one fork between on and off is its smallest grain. The word 'bit' comes from here.
Then he proved something remarkable: even down a noisy road, a message can arrive unspoiled if you attach spares cleverly — not by blindly repeating everything three times, but by computing a few check numbers and sending them along.
The click's journey is complete: finger, number, hundreds of millions of orders, dots of the screen. But one worker has not yet appeared. Painting millions of dots is really too big a job for the heart alone. The next piece is about the odd assistant who took it over.
The question that remainsIf 'at the same time' is an illusion of fast turn-taking — is a human's 'thinking of several things at once' truly simultaneous?