Designing Safe Software Systems Part 2 (2009)

A classic DrDobbs blog. Here's a link to Walter Bright's preceding part 1 blog:

http://www.drdobbs.com/architecture-and-design/safe-systems-...

This article mentions "dual path".

Can anyone confirm the tale that some aircraft/spacecraft have the same system built with different versions of Ada/Ada compilers on different hardware running at the same time for redundancy?