The Bridge - Issue 1, 2023 - 39

History Spotlight
required the space of several rooms. The designers of
the Apollo Guidance Computer (AGC) were given an
envelope of one cubic foot. The AGC was one of the
first computers to use integrated circuits and prioritize
computing tasks to speed up processing.
With a limited memory capacity of only 72 kilobytes,
would that be enough to guide Apollo to the Moon?
The memory was composed of copper wires woven
in a specific pattern in what was called " Rope
Memory. " Expert seamstresses threaded the wires
through magnetic rings (a wire going through the
ring was a 1, and a wire going around the ring was
a 0) to create the memory.
A major challenge in using rope memory was that
once it was installed, it could not be changed. That
meant the programming had to be right from the start.
Margaret Hamilton, who led the team developing the
programing put it into perspective: " When I first got
into it, nobody knew what it was that we were doing.
It was like the Wild West. There was no course in
it. They didn't teach it. " Her team of 400 engineers
and programmers not only developed the AGC's
programming, but their work also led to the creation
of " software engineering " as a distinct discipline.
During all the Apollo missions, the AGC was the sole
guidance system used as the spacecraft was on the
far side of the Moon and during the lunar module's
descent to the lunar surface. This AGC never failed
throughout the entire Apollo program.
Margaret Hamilton inside the Apollo Command Module mock-up and
posing with the AGC code. (Image credit: NASA/Draper Lab)
Burt Dicht is a member of IEEE-HKN's
Editorial Board and the former Director
of Student and Academic Education
Programs for the IEEE's Educational
Activities Department. He is also member
of HKN's Eta Chapter.
To Learn More About the AGC and Rope Memory:
IEEE Spectrum article " Software as Hardware: Apollo's Rope Memory "
29 Sept 2017 - https://spectrum.ieee.org/software-as-hardware-apollos-rope-memory and the
IEEE AGC Milestone: https://ethw.org/Milestones:Apollo_Guidance_Computer,_1962-1972
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39

https://spectrum.ieee.org/software-as-hardware-apollos-rope-memory https://ethw.org/Milestones:Apollo_Guidance_Computer,_1962-1972 https://hkn.ieee.org/ https://hkn.ieee.org/

The Bridge - Issue 1, 2023

Table of Contents for the Digital Edition of The Bridge - Issue 1, 2023