OT: This Swift thing

[Steven D'Aprano]

On Wed, 11 Jun 2014 19:41:12 +1200, Gregory Ewing wrote:

> Steven D'Aprano wrote:
>> Everything *eventually* gets converted to heat, but not immediately.
>> There's a big difference between a car that gets 100 miles to the
>> gallon, and one that gets 1 mile to the gallon.
> 
> With a car, the engine converts some of its energy to kinetic energy,
> which is subsequently dissipated as heat, so it makes sense to talk
> about the ratio of kinetic energy produced to energy wasted directly as
> heat.
> 
> But when you flip a bit, there's no intermediate form of energy -- the
> bit changes state, and heat is produced. So all of the heat is waste
> heat.

Not the point. There's a minimum amount of energy required to flip a bit. 
Everything beyond that is, in a sense, just wasted. You mentioned this 
yourself in your previous post. It's a *really* tiny amount of energy: 
about 17 meV at room temperature. That's 17 milli electron-volt, or 
2.7×10^-21 joules. In comparison, Intel CMOS transistors have a gate 
charging energy of about 62500 eV (1×10^-14 J), around 3.7 million times 
greater.

Broadly speaking, if the fundamental thermodynamic minimum amount of 
energy needed to flip a bit takes the equivalent of a single grain of 
white rice, then our current computing technology uses the equivalent of 
175 Big Macs.

(There are approximately 50 grains of rice in a gram, and a gram of rice 
is about 1.3 Calories. A Big Mac is about 550 Calories. You do the maths.)


-- 
Steven D'Aprano
http://import-that.dreamwidth.org/