On 30/09/2011 3:11 PM, Invisible wrote:
> I was under the impression that a capacitor only holds its charge for a
> very short period of time.
>

Depends what you mean by very short period of time. Most circuits that 
use large capacitors will have a discharge resistor in parallel to stop 
the capacitor holding the charge when the power is off. In domestic 
appliances such as radios and TVs, it was recommended that you wait 20 
minutes after switching off before working on them.
Also see:
http://en.wikipedia.org/wiki/Regenerative_capacitor_memory

> Regardless, have you ever actually seen an analogue computer with
> independently addressable memory cells? I haven't heard of such a thing.
>
What to answer first? I don't know, the only actual working valve 
computer I've ever been in the presence of was at Glasgow University, 
over 40 years ago. I've never had hands on experience working with them. 
But you would not use addressable memory as you would in digital 
computers. Remember that we are talking about voltage levels 
representing numbers. Also back in the day, what was being asked of then 
was much simpler and less complex so a lot of memory would not have been 
required.



>> Hmm! I don't know. You can do some very intricate and complicated things
>> with analogue electronics. Consider the brain. O_o
>
> Well, strictly speaking, every digital computer is also an analogue
> computer. They're just designed and used differently.

And use different principles.
http://en.wikipedia.org/wiki/Analog_computer#Electronic_analog_computers
or
http://www.bookrags.com/research/analog-vs-digital-computing-wcs/

-- 
Regards
     Stephen

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