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On Fri, 4 Oct 2024 23:46:20 -0000 (UTC), R Kym Horsell wrote:

> In alt.global-warming Dhu on Gate <campbell@neotext.ca> wrote:
>> On Fri, 4 Oct 2024 22:12:30 -0000 (UTC), R Kym Horsell wrote:
>> 
>>> In alt.global-warming Alan <nuh-uh@nope.com> wrote:
>>>> On 2024-10-01 01:40, R Kym Horsell wrote:
>>>>> In alt.global-warming Dhu on Gate <campbell@neotext.ca> wrote:
>>>>>> On Sun, 29 Sep 2024 23:19:24 -0500, AlleyCat wrote:
>>>>>>> Nebraska, USA: Within minutes, a single hailstorm reduced 14,000 solar
>>>>>>> panels, worth millions of dollars, into a pile of toxic debris-leaching
>>>>>>> materials like cadmium and lead into the soil.
>>>>>> Lotta folks don't get how fragile hi-tech shit is.
>>>>>> Dhu
>>>>> 
>>>>> 
>>>>> Long gone are the days of servicing your own vehicle.
>>>>> Apart from oiling some bearings you can't and sometimes are
>>>>> prohibited by law from fixing your own car.
>>>>> I was helping a neighbor recently and it turned out you
>>>>> needed to break an old mil grade encryption to even ask it here it hurt.
>>>>> 
>>>> 
>>>> What kind of car was that?
>>> 
>>> I pre-answered that. :)
>>> 
>>>> All cars built for sale in North America have had a standard OBD-II port 
>>>> that can be read by various scanners costing anywhere from $20...
>>>> ...to a lot more depending on complexity.
>>> 
>>> There's a theorem of computer science that roughly says
>> 
>> That's a "side effect" of completeness vs. consistency.  
>> 
>> IF you make a system "complete", that is covering all possible 
> ...
> 
> You're talking to someone that has been doing that stuff for 1/2 a lifetime. :)
> I like to think of it in terms of self-reference.
> Any system that has to look at itself will strike problems.
> Can you make a machine that can diagnose its own faults?
> What happens when the diagnostic part has a fault?
> 
> NASA always had an engineering policy that every mission-critical system
> had  to have triple redundancy. If not 3 identical systems then
> at least 3 different  subsystems had to be able to do the same job.
> But the point of failure generally was the part of the system that
> took the vote of the 3 identical systems to find out the majority-decision
> and switch out the subsystem that was wrong.
> 
> In MV you often see the central computer start up and ask various sub-systems
> to run diagnostics. The sub-systems poke some circuits and see if the
> results are what they expect. If so, they send an OK back to the start-up
> request from the central processor.
> 
> But the checking runs into a problem. If you have to check say 1 million
> bits to decide if your sub-system is working then how do you check
> they are all correct? A typical method is to use a hash. Boil the
> sequence of 1 million correct bits down into a 16 bit number.
> Take the hash of the million and check it against the 16 bits in PROM.
> But there is a logical problem. A million bits can have "many" more
> possible combinations of values than 16 bits. So it means there can
> be many problems that hash to exactly the "everything is OK" code.
> 
> But the hashing idea is cheap and everyone uses it "all the time".
> 
> So it's a minor miracle these days when you put your bread in a toaster
> that it cooks it for a couple mins, the toast pops up, and it's edible.

This is where the model for the 'net breaks down.  At this point in 
a real conversation I'd be offerin' to buy you a drink and pump you
some more ...

Dhu



-- 
Je suis Canadien. Ce n'est pas Francais ou Anglais.  
 C'est une esp`ece de sauvage: ne obliviscaris, vix ea nostra voco;-) 
 Duncan Patton a Campbell