system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they fit 2 billion transistors in a single square inch?
gpt
With great care.

Computer chips are generally made by laying down very thin coats of metal, then a chemical that reacts to light. Some of the chemical is exposed to a pattern of light while the rest is not, and then washed with a chemical solution that leaves the exposed area behind while the rest washes away. Then another layer of metal is laid down with the photo-sensitive chemical acting like a mask. Then the mask is washed away and the process repeated with a different pattern of light.

Using many repetitions of this process a 3D chip structure can be built up in a very, very small package.