> > Colin Geoffrey Hales wrote:
> >
> >> BTW there's no such thing as a truly digital computer. They are all
> >> actually analogue. We just ignore the analogue parts of the state
> >> transitions and time it all so it makes sense.
> >
> > And if the analogue part intrudes, the computer has malfunctioned
> > in some way. So correctly functioning computers are digital.
> >
>
> Not so in the case of all the computers we have. 0 and 1 are an
> interpretation put on a voltage by you and I. Depending on the voltage
> levels of the computer chip.
>
> Eg TTL <0.2 volts = 0, >4.2ish volts = 1
>
> If you get a logic gate and control the voltage fed to it you can see the
> transition from 0.2....4.whatever and up to 5 volts usually. It's a nice
> smooth transition. Let it go under it's own steam and the transition is
> very fast, but still all analogue real world potential measureed in
> conducting crytalline environment. You're talking to an electronic
> engineer here.
Of course they are analogue devices, but their analogue nature makes no
difference to the computation. If the ripple in the power supply of a TTL
circuit were >4 volts then the computer's true analogue nature would
intrude and it would malfunction.
Stathis Papaioannou
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