Ret'd
Is isn't just a 1's and 0's thing; from IEC 61508:
random hardware failure
failure, occurring at a random time, which results from one or more of the possible degradation mechanisms in the hardware
NOTE 1 - There are many degradation mechanisms occurring at different rates in different components and, since
manufacturing tolerances cause components to fail due to these mechanisms after different times in operation,
failures of equipment comprising many components occur at predictable rates but at unpredictable (i.e. random)
times.
NOTE 2 - A major distinguishing feature between random hardware failures and systematic failures (see 3.6.6), is
that system failure rates (or other appropriate measures), arising from random hardware failures, can be predicted
with reasonable accuracy but systematic failures, by their very nature, cannot be accurately predicted. That is,
system failure rates arising from random hardware failures can be quantified with reasonable accuracy but those
arising from systematic failures cannot be accurately statistically quantified because the events leading to them
cannot easily be predicted.
So, the 'fault' may be a systematic feature of the process, but the 'failures' are still randomly distributed, even in a narrow band. eg the composition of an alloy is incorrect because of a systematic 'fault' in the process. The resulting batch of products will probably exhibit a random failure pattern similar to that of a 'perfect' batch but shifted to some extent.
Anyway, we creep somewhat and can take this elsewhere. Hope your hols were good.
cheers
sw