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Comment by mongol | Hacker News Reader

How reliable are / were tapes?

There are numerous articles on the Shuttle's computers. I seem to remember the Apollo had quadruple redundancy, AND an extra backup failsafe, and lots of protection from degradation from cosmic rays, and I think the Shuttle had 5 computers too. I'm sure there's lots available, frmo NASA and other sources. https://history.nasa.gov/computers/Ch4-3.html

The Shuttle had four main computers hooked together to form a redundant system, and then a fifth backup computer which was only capable of handling launch and reentry/landing. In the unlikely event that all four main computers couldn't be reprogrammed, the fifth one could still get everybody home.

Aha thanks, it was the shuttle that had the 4-way redundancy thing! I got scared of my memory, not being able to find verification quickly online, so instead wrote something less true!

The Apollo Guidance Computer used core rope memory [1] as ROM and magnetic-core memory as RAM. Both are non-volatile.

The command module did not have a redundant computer or memory, but the lunar module came with a second computer [2] of a different type and running different software.

What you remember is probably the Gemini Guidance Computer's tape drive system, which consisted of three identical tape drives that were connected to the computer through a voter circuity.

[1] https://en.wikipedia.org/wiki/Core_rope_memory

[2] https://en.wikipedia.org/wiki/Apollo_Abort_Guidance_System

By the standards of the time, a relatively large amount of data could be stored in a small installed volume of core rope memory: 72 kilobytes per cubic foot, or roughly 2.5 megabytes per cubic meter.

Re: core rope

Jesus. Now it’s TB/cm...

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