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Elliotte Harold wrote:
> Rick Marshall wrote:
>
>
>> 2) software systems do degrade, as mentioned by changing external
>> systems. but with modern hardware reliability i think hardware now
>> has more in common that software in this respect. eg most of the
>> hardware upgrades we complete are now due to obsolesence rather than
>> failure
>
>
> In computers, perhaps. But in airplanes, automobiles, lawnmowers,
> microwave ovens, refrigerators, and many other forms of hardware, no.
> The fact is a modern computer doesn't have all that many moving parts,
> which is what leads to parts wearing out. (There's the hard drive, the
> fan, the CD-tray, maybe a button or two, anything else?) However, even
> well-lubricated, well-maintained motor based hardware experiences
> significant friction that will degrade parts over time. Off the top of
> my head I don't know why microwave ovens wear out, but they certainly
> do as well. There's just no equivalent to friction-driven
> wear-and-tear on software.
>
electronics 101 - the main cause of electronics failure is heat induced
degrading of transistor gates (the doping materials under thermal stress
move around narrowing the gate to the point of failure). this applies as
much to microwaves as it does to microprocessors.
the main reason modern devices are more reliable is that we are winning
the heat war - lower voltages = less heat for given performance. more
gates means more heat. hence cpu fans etc. so long as the cpu fan keeps
working - providing adequate cooling - a modern pc will run for years
trouble free. keep the dust from your bearings and suspect the cpu when
software starts playing up - replace the fan.
i have reliability problems from some point of sale software because the
pc's get housed in enclosed spaces and cook themselves. but the pc dies
slowly so it looks at first like bizarre software faults, but in reality
it's random temporary circuit failures in the cpu. we debug the software
by fixing the cooling!
maybe we need holistic software development as a discipline ;)
rick
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