How many?

A phone chip can hold billions of them, packed into an area about the size of your thumbnail.
That chip is made of silicon. A material refined from ordinary sand.

You may hear chipmakers talk about "5 nanometer" or "3 nanometer" chips. That number is a manufacturing label, not a ruler you can place across one transistor. The real point is simpler: the switches are unimaginably small.

Billions of switches. Packed into a piece of silicon. Flipping on and off billions of times a second.