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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Ada student homework ?
Date: 2000/11/18
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In article <5E93Ivxu6GwO@eisner.decus.org>,
  Kilgallen@eisner.decus.org.nospam (Larry Kilgallen) wrote:
> In article <8utul0$vnv$1@nnrp1.deja.com>, Robert Dewar
<robert_dewar@my-deja.com> writes:

> that does not mean there are crash-proof operating
> systems, because the implementation is subject to human
> frailties.

Well, with obvious exceptions like THE, operating systems are
rarely certified to be bug free. But in pragmatic terms,
operating systems like VMS and IBM mainframe systems are
close enough. Indeed in practical terms, OS/2 also reachest
this criterion.

An interesting question to ask yourself. How often have you
seen Windows start up screens in places where they do not
belong (such as on airport monitors -- where I saw the
screen a couple of weeks ago :-)

By comparison, how often have you seen OS/2 startup screens
on your friendly ATM machine?

Of course all things are relative, but it really is possible
to achieve the engineering equivalent of crash-proof, which
is not really a mathematical property, but rather the stage
at which operating systems frailty is not the weak link in
the chain (there is generally no point in building software
that is orders of magnitude more reliable than the hardware
for example :-)




>
> So those "good" operating systems are not really crash-proof,
> just so crash-resistant that they seem crash-proof when they
> are compared to the competition.
>
> As an example, consider that Windows NT uses the memory
management
> hardware and still gets lumped by practical experience into
the
> "not crash-proof" pile.
>


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