TDP is typically defined as Thermal Design Power, the amount of power (heat) that a cooler must dissipate in order to keep a silicon chip within its operating temperatures. While Intel and AMD disagree as to what test to run to measure this, both agree that it’s a measurement of waste heat output from a chip.
Reading through the Nvidia GeForce GTX 580 1.5GB review
guide threw up a new definition, however: ‘TDP is a measure of maximum power draw over time in real world applications.
’ Even if Nvidia’s definition is the correct one, I have to wonder why it wanted to use the term in this way at all.
The use of the term TDP will inevitably lead to comparisons between the power consumption of Nvidia’s graphics cards and heat output of CPUs and GPUs. By defining TDP as an input– and, in fact, as the maximum power draw of an entire card, rather than just the GPU – Nvidia is making its product look comparably terrible. A 6-core LGA1366 Core i7-980X Extreme Edition has a TDP of 140W, likewise an Athlon II X6 1090T Black Edition, but with a ‘TDP’ of 255W Nvidia is making the GTX 580 1.5GB seem to be twice as hot or twice as power hungry as those CPUs.
And for what? Detractors and the flippant will say that all this power is merely being use to play some games that can run just as well on an Xbox – what a waste of valuable resources!
Of course, you and I know better. For a start, some of the best games around require fast, modern PC hardware and many aren’t even available for consoles. More pertinently, we know that TDP should be a measurement of waste energy (heat, unless something goes drastically wrong) and not, as Nvidia says, a measurement of maximum input power.
Lars Weinand, Senior Technical Marketing Manager, EMEA, told us that, ‘The problem with TDP is there is no “standard” for this. So everyone is measuring TDP in a different way and TDPs are only really comparable within the same manufacturer… We are using TDP in a way that makes most sense for us.
’ Even Lars ultimately suggests that we put more faith in our power consumption tests than a number written on a spec sheet.
But for all that, why would Nvidia invite the kind of criticism and confusion I’ve briefly outlined? It’s not as if a maximum board power of 255W is especially high for a top-end card – others have hit 293W and no-one has complained. Nvidia’s definition of what it means by TDP may be sufficiently clear that I don't care what term is uses, but Nvidia’s marketing department really should.