>> Unless, by "how my PC works", you mean why it needs a million tiny (or
>> not so tiny) capacitors on the motherboard,
>
> I have to admit, I have frequently wondered why this *digital* device
> has hundreds of *analog* components on it (mostly capacitors and
> inductors). I mean, I get why they're on the motherboard rather than on
> the silicon die, but why do you need them at all?

Aha - so you are not just interested in a fictional perfect logic device 
then? :-) Start at the beginning of the book. All will make sense.

> Is there a simple relationship between circuit design and heat output?

voltage x current

> I
> mean, is it something as simple as number of switching elements and how
> fast they switch per second? Or is it something more complicated?

As clipka mentioned, a transistor used in digital circuits is either in 
a state where the current flow is zero ("off") OR the voltage drop is 
zero ("on"), so heat output is usually zero. It's switching between 
those two states, when both voltage and current are non-zero, that 
significant heat is dissipated within the transistor.

> Interesting. I didn't realise the efficiency was still that low.
> (Obviously incandescent bulbs are notoriously inefficient. But I thought
> LEDs were a bigger step forward than that...)

https://en.wikipedia.org/wiki/Luminous_efficacy

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