🚀 go-pugleaf

In article <g49318.at.ln@127.0.0.1>, anahata@freereed.demon.co.uk (Anahata) writes:
|> On Thu, 18 Nov 1999 18:25:13 +0000, John Underwood
|> <john@jsunderwood.demon.co.uk> wrote:
|> In theory, that could happen.  However, computers spend much of their time
|> making address computations, and a simple numerical error in an address is
|> likely to cause visible effects, either with a progam going out of control
|> or with the OS trapping an illegal access.
|> 
|> I would expect that in most cases a system will be error free or the error
|> rate will be high enough that the result will be obvious.

Not necessarily.  You do not know where the critical path(s) (the section of the 
chip which is closest to being broken) is located.  If it is in logic which is
used for address calculation, then you will probably notice an error quickly.  If
it is in the microcode, then you will almost certainly notice it.  However, it
could be somewhere a bit more innocuous; it is quite possible that the failure 
could be located in the FPU, given their complexity. Or maybe in the path
writing data out to memory.  If you are doing tax rate calculations, which would 
probably use the FPU, then you might get unnoticed errors in your data.  I'm not
sure I'd like to take the risk of corrupting the data going through my CPU. It's
a matter of personal choice whether you overclock or not.

Incidentally, when you get close to the limit of the speed of the device, there 
are other factors which could cause errors - crosstalk, for example, is where 
two wires run parallel together for a reasonable distance.  The capacitance 
between the two wires means that if they both change state at the same time, 
they will each affect the speed of the other.  
If both wires change from 0 to 1, then they will change particularly fast, 
whereas if one changes from 0 to 1 and the other changes from 1 to 0, then 
they will both change particularly slowly.  Factors like this are enough to 
push the delay  'over the edge'.  So, whether your device fails depends not 
only on what it is doing at the time, but also the data you are using.  

-- 
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