The smartphone in a pocket today has more processing power than the room-sized machines that once calculated missile trajectories. Here's how computing got from mechanical gears to a device that fits in one hand, in a series of turning points rather than one single invention.
The "How Computers Work" article in this series explained that every modern computer, at its core, is built on binary code and processes numbers through hardware built for exactly that purpose. That foundation didn't appear all at once — it's the result of roughly two centuries of engineering, spanning mechanical gears, room-sized vacuum tube machines, and finally the microchips that made a computer small and cheap enough to fit in a pocket. This guide walks through that path as a handful of genuine turning points, rather than a simple timeline of dates.
In the early 1800s, the English mathematician Charles Babbage designed the Analytical Engine, a mechanical machine intended to perform calculations automatically using a sequence of instructions — conceptually, the earliest known design for what a modern computer does, despite being built entirely from gears and levers with no electricity involved. Ada Lovelace, working alongside Babbage, wrote what's now considered the first computer program, an algorithm meant to run on that never-fully-built machine, and is widely regarded as the first computer programmer as a result.
The Analytical Engine was never fully constructed in Babbage's lifetime, yet its core idea — a machine following a stored, changeable sequence of instructions rather than being built for one fixed calculation — is the same basic concept the "What Is Coding?" article in this series describes as a program.
The 1940s saw the first working electronic computers, built using vacuum tubes rather than mechanical parts, which allowed calculations at speeds no mechanical machine could match. These early machines were enormous, filled entire rooms, generated significant heat, and were built for a single specific purpose, such as calculating artillery trajectories during wartime — a sharp contrast to a modern computer's ability to run any of thousands of different programs on the same hardware.
The invention of the transistor in the late 1940s replaced the bulky, fragile, heat-generating vacuum tube with a much smaller, more reliable, and far more energy-efficient component that did the same basic job of controlling electrical signals. Computers built with transistors in the following years shrank dramatically in size while becoming significantly more dependable, setting the stage for computing to spread beyond a handful of government and university labs.
| Era | Core Technology | Typical Size |
|---|---|---|
| 1940s | Vacuum tubes | Filled entire rooms |
| Late 1940s–1950s | Transistors | Large cabinets, still room-scale |
| 1960s onward | Integrated circuits | Increasingly compact |
In the late 1950s and 1960s, engineers found a way to place many transistors onto a single small piece of silicon, called an integrated circuit, rather than wiring individual components together separately. This innovation is what eventually made the microchip possible — a component small enough to fit an entire processor's worth of transistors onto a chip smaller than a fingernail, and it's the direct technological ancestor of the CPU covered in the "How Computers Work" article in this series.
The trend of fitting more transistors onto the same size of chip roughly doubled every couple of years for decades, an observation known as Moore's Law, which is a large part of why computers became dramatically more powerful and dramatically cheaper at the same time across the following decades.
Through the 1970s, microchips became cheap and small enough that a computer no longer needed to be an institutional, room-filling machine — it could be built for a single person to own and use at home or work. Companies including Apple, IBM, and Microsoft played major roles in the following decade in turning that possibility into an actual consumer product, complete with a graphical interface, similar in concept to what the operating systems article in this series described, that made a computer usable without specialised training.
Personal computers becoming widespread solved the problem of individual computing power, but each machine still largely worked in isolation. The internet, whose technical workings are covered in a separate article in this series, solved that by connecting individual computers into a single global network, turning a personal computer from a standalone calculating device into a gateway to every other connected machine and, eventually, to the modern web.
Smartphones, introduced widely in the late 2000s, combined the microchip's miniaturisation, the personal computer's usability, and the internet's connectivity into a single pocket-sized device carried by billions of people constantly. That same combination of cheap, powerful, widely available computing and vast connected data is also the direct foundation for the machine learning and large language model advances covered elsewhere in this series — techniques that existed conceptually for decades, but needed the scale of modern hardware and data to actually become practical.
Every turning point in this history solved the same underlying limitation of the one before it — mechanical calculation gave way to electronic speed, vacuum tubes gave way to reliable transistors, room-sized machines gave way to a personal device, and isolated computers gave way to a connected network. The device in a pocket today isn't really a single invention; it's the accumulated result of roughly two centuries of solving one bottleneck after another, each one covered in more technical depth elsewhere throughout this series.
10 questions. Select an answer for each, then submit to see your score instantly.