I wonder if the very low density (relatively speaking to today) make them more robust against gamma-rays and other radiation problems once outside the atmosphere?
if I remember correctly, and it's been decades of course
four of the computers ran in parallel with the exact same instructions in case one failed or came up with a wrong answer
and the fifth computer was the "decider"
is that understanding correct?
ah I see now you mention
Eight networks were assigned to flight-critical systems,
with each CRT display and engine controller connected to four networks for redundancy.As far as redundancy, it's complicated. During critical flight phases, four computers would run the main software (PASS, Primary Avionics Software System), while the fifth computer was ready with the Backup Flight Software (BFS). The backup software was written by a completely different team to ensure that a software bug couldn't crash all the computers at once. In orbit, they used fewer redundant computers to free up computers for payload operations and stuff.
The four computers constantly checked the results from each other and would vote out a faulty system. Voting ensured that a bad computer couldn't vote out the good ones (Byzantine failure). Moreover, the actuators hydraulically voted on the results from the computers: if one computer tried to push a valve in a different direction, the three good computers would physically overpower the bad computer's action at the level of the hydraulic pistons.
Yes. Large size transistors (and other IC components) are less impacted by the radiation problems that exist outside the relative security of the atmosphere. Most radiation hardened IC circuity is many process sizes larger than whatever the current state of the art tiny process sizes happen to be at any given time.
But note I said "less impacted". Given sufficient radiation, things will have issues, which is why items like the Shuttle carried the redundant computers, to cover for the possible lucky-strike impacts.
FYI - The link for Peter Kogge is broken and should probably link to https://en.wikipedia.org/wiki/Peter_Kogge