Imagine debugging your code by walking through a room the size of a tennis court, listening for the faint tink of a burnt-out glass bulb among 17,000 others. That was daily life for the operators of ENIAC in 1946 — and it's the origin story of every computer you've ever touched.

The first-generation computer was defined by one component: the vacuum tube, a fragile glass envelope where a heated cathode boiled off electrons that were steered by a charged grid. In effect, each tube was a switch — the direct ancestor of the transistor in your phone's SoC. But where a modern CPU packs tens of billions of switches into a fingernail, ENIAC needed a warehouse for a fraction of the compute power of a 1980s pocket calculator.

The engineering constraints were brutal:

• Heat. ENIAC drew 150 kilowatts. The room had to be industrially cooled, and even so, the ambient temperature routinely climbed past 50 °C.
• Reliability. With thousands of tubes each having a modest lifespan, statistics guaranteed failures. Engineers ran the tubes at reduced voltage — derating — to extend life, and they never turned the machines off, because the thermal shock of powering up killed more tubes than continuous operation.
• Bugs. Yes, literal ones. Grace Hopper's famous moth, taped into the Harvard Mark II logbook in 1947, is the etymological seed of the word we still use today.

What's genuinely surprising is how quickly the vacuum-tube era ended. The generation lasted barely a decade. IBM's 700 series, Britain's Manchester Mark 1, the Soviet BESM — the peak commercial output of tube computing was already being obsoleted by transistorized machines by the late 1950s. By 1960, buying a new tube computer was like buying a new steam locomotive: possible, but eccentric.

And yet the intellectual scaffolding built during those years — stored-program architecture, subroutines, assemblers, the first compilers, even the first computer music (an Australian CSIRAC played "Colonel Bogey March" in 1951) — all of it was invented on machines that measured RAM in tubes, not gigabytes. Every abstraction a modern programmer takes for granted was first proven out on hardware that hummed, glowed orange, and occasionally set itself on fire.

There's a final wrinkle that vindicates the old technology. Vacuum tubes are radiation-hard in ways silicon isn't, and they can operate at temperatures that fry semiconductors. NASA and defense researchers have quietly revived vacuum-channel transistors — nanoscale tubes etched onto chips — for applications in space and high-frequency electronics. The tube didn't really die; it just got very, very small.