On the Space Shuttle, four computers with identical software ran redundantly, and a fifth with independent software was used to detect errors. http://en.wikiped

On the Space Shuttle, four computers with identical software ran redundantly, and a fifth with independent software was used to detect errors. http://en.wikipedia.org/wiki/Space_Shuttle http://en.wikipedia.org/wiki/Space_Shuttle http://www.hq.nasa.gov/pao/History/computers/Ch4-4.html http://www.hq.nasa.gov/pao/History/computers/Ch4-4.html This was, of course, very expensive, and made software changes a very difficult and slow process.