In 1947, there was only one transistor. According to TechInsight’s forecast, the semiconductor industry is on track to produce almost 2 billion trillion (1021) devices this year. That’s more transistors than were cumulatively made in all the years prior to 2017. Behind that barely conceivable number is the continued reduction in the price of a transistor, as engineers have learned to integrate more and more of them into the same area of silicon.

Scaling down transistors in the 2D space of the plane of the silicon has been a smashing success: Transistor density in logic circuits has increased more than 600,000-fold since 1971. Reducing transistor size requires using shorter wavelengths of light, such as extreme ultraviolet, and other lithography tricks to shrink the space between transistor gates and between metal interconnects. Going forward, it’s the third dimension, where transistors will be built atop one another, that counts. This trend is more than a decade old in flash memory, but it’s still in the future for logic (see “Taking Moore’s Law to New Heights.”)

Perhaps the crowning achievement of all this effort is the ability to integrate millions, even billions, of transistors into some of the most complex systems on the planet: CPUs. Here’s a look at some of the high points along the way.