Apollo Guidance Computer
The computer that navigated Apollo spacecraft to the Moon, with about 74 kilobytes of memory and software woven into wire.
The Apollo Guidance Computer, or AGC, was designed at the MIT Instrumentation Laboratory under Charles Stark Draper. A copy flew in both the command module and the lunar module. Astronauts used a keypad and display unit called the DSKY to enter commands such as verb and noun codes.
The AGC was among the first computers to use integrated circuits in volume. Its programs were stored in core rope memory, where wires woven through or around tiny magnetic cores represented ones and zeros. Raytheon workers wove the ropes by hand. Margaret Hamilton led the software engineering team at MIT. During the Apollo 11 landing in July 1969 the computer raised '1202' alarms because it was overloaded, and its priority-based design dropped lower-priority tasks and kept the landing running.
Why it matters
The AGC showed that software could be trusted with human lives and helped establish software engineering as a discipline. Its small size drove advances in integrated circuits.
Key facts
- About 36,864 words of fixed rope memory and 2,048 words of erasable memory.
- Used 15-bit words plus a parity bit.
- Weighed about 70 pounds.
- Programs were woven into core rope memory by hand.
- Margaret Hamilton led the software team.
Sources
- Mindell, David A. Digital Apollo: Human and Machine in Spaceflight. MIT Press, 2008.
- Hall, Eldon C. Journey to the Moon: The History of the Apollo Guidance Computer. AIAA, 1996.
- NASA, Apollo 11 Mission Report and Apollo Flight Journal (history.nasa.gov/afj).