[robryk]

Note that this was not a code patch: This was a sequence of changes to the program state that tricked it into ignoring the abort switch. The code itself was stored in read only core rope memory, so it was physically impossible to change it (the memory was written by appropriately winding wires around ferrite cores).

EDIT: More details (in the form of a puzzle): http://www.ibiblio.org/apollo/#Final_exam_for_the_advanced_s...