Technology has changed quickly over the years, charging forward at a mind-blowingly fast rate since the inception of semiconductors. Before semiconductor were invented, computing mechanics relied on slow and bulky vacuum tubes. With silicon, the world of computing became, well, small. Not small in the sense of popularity, as clearly computers have exploded in popularity over the years, but rather small in regards to their size.
In the days of vacuum tubes, computers were large. Much larger than a smartphone and a whole lot less powerful. By manufacturing transistors out of silicon, it became possible to fit them on a microchip, which eventually led to incredibly small gadgets like the smartwatches that we have today.