From Bjorn Freeman-Benson’s talk Airplanes, Spaceships, and Missiles: Engineering Lessons from Famous Projects
Bjorn is discussing the ferrite core memory of the Apollo guidance system.
These are very, very robust memory systems. … But the problem is that they actually have weight to them. Core memory actually weighs a bunch, so when you’re writing your program for the lunar module … every line of code that you wrote had a consequence in weight. And you could measure how heavy your code was at the end of a compile line. … It’s an interesting analogy to keep in mind because in fact even today our code has weight. It doesn’t really have physical weight … Our code has psychological weight because every line of code we write has to be maintained. It has to be supported. It has to be operated.
Here’s the video. The context of the quote begins at 33:14.