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/ -- https://mail.python.org/mailman/listinfo/python-list