Chuck writes:

> The PC was designed to be cost effective and so its components are not as
>  rugged as those found in that HP3000 you paid 100 times as much for. Also,
>  how many of those HP3000 components have been replaced over the years?

Chuck's point is well taken. One of the most important things to consider in
the design of any piece of equipment is the environment into which it is to
be placed. In the case of PC's, it's one of extremely rapid evolution, and
there's simply no reason to overbuild these devices. Moreover, there is
expected to be no one present to work on these devices, debug them, and
replace defective components.

In that regard, I was reading the other day a fact that actually shocked me
when I first read it, but one that makes otherwise perfect sense: B-17's were
designed during WWII for only 100 takeoffs and landings. It was felt that
building the machines for any greater duty cycle than that was merely wasted
effort.

The reason for that design criterion was that mortality rates were so high
over Europe for American bomber crews that a crew who survived 25 missions
over Germany were given rotation home and out of the war, but very few ever
made it. Indeed, the fact that the "Memphis Belle" was the first achieve that
status was the whole reason behind the recent, mostly true movie about the
"Belle."

If 25 missions was unlikely to be survived, 100 mission survival was many
sigmas out, essentially zero probability of survival. Moreover every part of
the B-17 was designed to be as simple and as easily replaced as it possibly
could be so that damaged aircraft could be canabalized and their parts reused
on other airframes.

Nonetheless, the reliability and the ruggedness of the B-17's became
legendary. Cheap and simple doesn't always mean poor quality.

Wirt Atmar

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