🚀 go-pugleaf

In article <x2emdp17uo.fsf@zdbaora.nat.bt.com>, Robin Smith <smithrc@zdbaora.nat.bt.com> writes:
|> dsmith@bristol.nospam.st.com (Dave Smith) writes:
|> 
|> > Rubbish (sort of).  Device Speed is always a function of temperature, i.e. the
|> > hotter it is, the slower it runs.  Extra cooling in overclocked machines has two
|> > functions:
|> >  o Stop the device from exceeding a safe temperature limit, beyond which the chip
|> >    can be physically damaged
|> >  o Keep the device as cool as possible, to maximise the speed at which it can run
|> >    The colder a device is, the faster it will run.
|> > 
|> 
|> I'm just back from the pub so restraint mode=unrestrained
|> 
|> Bollocks, the phrase "Device Speed is always a function of
|> temperature" is wrong. "temperature is a function of device speed" is
|> correct. CMOS only uses current ( generates heat ) when it switches,
|> the faster you switch a CMOS circuit the hotter it gets.

Correct.  What generates this heat?  Resistance.  The capacitance of a device is 
not affected by temperature, but the resistance *is*.  Ironically, the hotter
a device is, the higher the resistance, so the more heat it generates.

|> The phrase "Keep the device as cool as possible, to maximise the speed
|> at which it can run. The colder a device is, the faster it will run."
|> is patently untrue. Keeping the temperature will stop the chance of
|> breakdown by stopping failures due to thermal problems however it will
|> not stop electrical limits ( capacitance etc. ). 

You appear to have forgotten elementary electronic theory.  Simply putting
parasitic capacitance (capacitance between the node you're interested in, and 
ground) in a circuit will not slow it down; the speed reduction is caused by the
combination of capacitance with the resistance of the driving transistor
(resistance of the wire interconnect is also becoming an increasingly important
factor as we move towards deep-sub-micron device dimensions).  The resistance of
the device increases as temperature increases, and the delay is directly
proportional to that resistance.

As I said before, any device will be able to run faster if you can keep it below
it's normal operating temperature (at normal clock speed).

|>                                                   If we could cool the
|> systems enough to make them run fast enough we would be using ZX-81s
|> in liquid nitrogen clocking at 1GHz. Now there is a thought!

If we're going to do that, then use superconducting materials for interconnect...

Anyway, this has now gone waaaaaay off-topic.

-- 
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