The Apollo Guidance Computer that flew Neil Armstrong to the moon in 1969 had 64 kilobytes of memory and ran at a clock speed of 0.043 megahertz. A modern smartphone has roughly a million times more memory and runs at thousands of times that speed. A single high-resolution emoji on a modern phone takes more storage than the entire Apollo navigation software.

The computer was custom-built at MIT for NASA. Its memory was, quite literally, a physical thing. Copper wires were woven by hand through tiny donut-shaped magnets called ferrite cores, in a system known as core rope memory. To program a 1, a wire passed through the donut. For a 0, it bypassed it. Programs were stitched into the hardware by skilled workers — many of them women hired for their textile experience — and could not be modified after assembly.

Margaret Hamilton led the software engineering team. She is credited with coining the term software engineering. Because the code could not be patched after launch, every line had to be flawless under all conditions.

The computer's most famous moment came during Apollo 11's lunar descent. Just minutes from touchdown, alarms started flashing — error codes 1201 and 1202. The computer was overloaded. A misconfigured radar was sending unnecessary input streams, and the system was processing more data than it had cycles for.

But Hamilton had built priority scheduling into the code. The computer began shedding low-priority tasks while keeping critical landing computations running. Mission Control radioed approval to continue. Armstrong landed Eagle on the lunar surface with reportedly fewer than thirty seconds of fuel remaining.

A modern phone has more memory, runs faster, and is regularly dropped on the floor. The Apollo Guidance Computer ran for two weeks of mission time without a single hardware fault.