Hardware/doc preservatoion, was Re: rarest computers.

[Paul Koning]

>>>>> "Paul" == Paul Koning <pkoning at equallogic.com> writes:

>>>>> "Steven" == Steven N Hirsch <shirsch at adelphia.net> writes:
 Steven> On Wed, 4 Aug 2004, ben franchuk wrote:
 >>> PS. Years ago in BYTE ( early 1990's? ) they had spoke up of a
 >>> CPU designed for reliable operation for real time control of
 >>> things like power plants or subways or aircraft. They claimed it
 >>> was so simple that programs could be proven to be bug free. I was
 >>> wondering if they manufactured or sold any the devices.

 Steven> That would be the British "Viper" CPU.  Computational theory
 Steven> suggests (proves, perhaps? - it's been a few years) that use
 Steven> of hardware or software stacks renders behavior
 Steven> indeterminate.

 Paul> Baloney.  Anyone who has paid any attention to Dijkstra knows
 Paul> that such a statement would have to be complete and utter
 Paul> nonsense.

PS. It is certainly true that programs can be proven to match their
specification.  That's not quite the same as proving them bug free --
it now requires the specification to be bug free.

But such proofs in no way require the absence of a stack.  That's
actually rather obvious, because any program that uses a stack can be
rewritten into a program that does not use one.  But in fact such a
rewrite does not help readability at all.

It probably is not a coincidence that the scientist who did much early
work on stacks is also the scientist who spent a lifetime working on
program correctness (E.W.Dijkstra).

	    paul