Space Shuttle uses 2-version programming

[andrew morton]

> The Space Shuttle does *not* use N-version programming - it uses identical
> instances of the same software, and uses redundancy to account for hardware
> failures.  Again, a good explanation of the methodology used is at
> http://en.wikipedia.org/wiki/Space_shuttle.

I wonder if Jeremy read the Wikipedia article he linked to...  currently it
reads:

  "The Backup Flight System (BFS) is separately developed software running
  on the fifth computer, used only if the entire four-computer primary
  system fails. The BFS was created because although the four primary
  computers are hardware redundant, they all run the same software, so a
  generic software problem could crash all of them."

  http://en.wikipedia.org/w/index.php?title=Space_Shuttle&oldid=141962184

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