On the subject of diversity and reliability, I found the following in RISKS 3.41:
Q11: True or False? Computer programs prepared independently from the same
specification will fail independently.
A11: False. In one experiment, 27 independently-prepared versions, each
with reliability of more than 99%, were subjected to one million
test cases. There were over 500 instances of two versions failing
on the same test case. There were two test cases in which 8 of the
27 versions failed. (Knight, Leveson and StJean, "A Large-Scale
Experiment in N-Version Programming," Fault-Tolerant Computing
Systems Conference 15)
RISKS 3.41 can be had at the following URL:
http://catless.ncl.ac.uk/Risks/3.41.html
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