[Knufire]

NOTE: I am aware that TDP is a relatively accurate number to use for 100% load power consumption.

I guess my question is more about the physics behind the number, just something that I keep wondering about every once in a while. Technically TDP is thermal dissipation power, which is the amount of thermal energy the card is releasing over time.

If TDP = power consumption, this would mean that 100% of the electrical energy is converted into thermal energy, meaning a processing unit is nothing more than a heat producer.

However, it is doing calculations, performing functions, powering a fan, etc, etc. The various components on the card have to be doing a certain amount of work, which requires a certain amount of energy.

Therefore, shouldn't TDP be slightly lower than power conusmption?

[mokrunka]

You are correct in saying that actual heat output is not equal to the power consumption of the CPU. That would be an entirely useless CPU!!!

More typically, TDP stands for Thermal Design Power. It means that whatever you are using to cool the electronic component should be capable of dissipating this much heat, in order to keep the part from failing/malfunctioning/melting into a pile of goo when under the "maximum perceived load" (usually a reasonable estimate of the maximum amount of power the part will require).

It does not mean that if your TDP=100W, then your CPU is using 100W; only that for whatever amount of power the CPU IS using, it requires the dissipation of 100W in order to function properly at that performance level.

Hopefully that isn't more confusing...

[Knufire]

Originally Posted by mokrunka

You are correct in saying that actual heat output is not equal to the power consumption of the CPU. That would be an entirely useless CPU!!!

More typically, TDP stands for Thermal Design Power. It means that whatever you are using to cool the electronic component should be capable of dissipating this much heat, in order to keep the part from failing/malfunctioning/melting into a pile of goo when under the "maximum perceived load" (usually a reasonable estimate of the maximum amount of power the part will require).

It does not mean that if your TDP=100W, then your CPU is using 100W; only that for whatever amount of power the CPU IS using, it requires the dissipation of 100W in order to function properly at that performance level.

Hopefully that isn't more confusing...

I'm aware xD. The question I guess I was trying to ask is what in physics makes the physical work done by the CPU so little that TDP roughly equals power consumption.

[Bobnova]

There is no physical work done by the CPU.
All electrical energy consumed by the CPU is released as heat, one way or another.

TDP is set by the class of CPU by and large, your CPU may not actually hit TDP if it isn't the worst piece of silicon to be assigned to that bin.


EDIT:
To elaborate a bit on GPUs, as they have mechanical bits that actually do some physical work.
The cooling fan for instance consumes a decent amount of power, the GTX480 unit for instance ate something like 24 watts. Of that a decent chunk was lost to heat right on the spot in the motor.
Another chunk (smaller) was lost to heat via friction with the air the fan spinning in, as well as the general agitation of the air. Air doesn't like getting banged around.
The faster the fan is turning (in its normal operating range), the less efficient it is at moving air. All energy that does not go into moving air becomes heat on the spot. The harder it is banging the air around the hotter the air gets, too. (This, as a sidenote, is the #1 issue with roots superchargers. They abuse the hell out of the air, resulting in rather high output temps for the pressure generated)

Just to finish things off, all the air it has forced to move comes to a stop via friction eventually. Friction of course is the conversion of kinetic energy to heat energy.

So in the longish run all the electrical energy put into a fan turns into heat.