What Is Thermal Design Power? [Technology Explained]

tdpthumb1   What Is Thermal Design Power? [Technology Explained]Acronyms are not uncommon in the world of computer hardware. CPU, GPU, RAID, SSD…the list goes on.

Many of these acronyms have entered the common geek vocabulary. Most people know what a CPU is (at least they think they know) but others are more obscure. One example is TDP, which stands for Thermal Design Power. This specification is rarely made available in marketing material, but it’s important for developing a full understanding of a processor’s potential.

The Basics Of TDP

Thermal Design Power, or TDP, is a statistic that is expressed in watts. It’s an expression of the amount of power a processor is expected to dissipate to prevent overheating. For example, a part with a 12W TDP will could potentially be cooled by a very small fan or a passive heatsink. A part with a 95W TDP, on the other hand, is going to need a substantial dedicated heatsink with a reasonably large fan (probably 80mm).

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You’re most likely to see these three little letters attached to a CPU or GPU’s spec sheet, but it can be used to express the maximum power draw of a wide variety of electronics.

Since this metric is based on power, it’s a useful way to understand how much power a component will draw relative to the competition. A lower thermal design power generally results in lower power consumption which means greater battery life.

TDP is a self-reported metric. Each manufacturer announces it based on their own findings. Such a system often results in exaggerations, but in this case, there’s reason to trust the numbers. If TDP was not reported with reasonable accuracy it would cause all sorts of problems, as companies would be building products that can’t properly handle the part.

Examples Of TDP

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As stated above, the various parts can have vastly different TDPs. Perhaps the most common example is the difference between a modern ARM processor designed for smartphones and a desktop processor designed for home and office PCs.

The Snapdragon processors found in so many of today’s smartphones have stated TDPs of .5 to 1 watt, while a Core i5-2500 has a TDP of 95 watts. That’s a massive difference, and representative of the difference in each part’s power consumption and performance.

Modern GPUs have even higher TDPs, with some parts quoting a TDP of over 225 watts. This doesn’t mean that the part will be consuming that much power all of the time, but it does mean that engineers designing the part consider it possible that this level of power draw will need to be dissipated for a sustained period of time.

How TDP Knowledge Can Benefit You

Now that you know this information you may be wondering how it can be useful. While TDP is commonly quoted, it’s not a precise gauge of power consumption or performance, but rather an engineering guideline.

Still, having a look at the thermal design power of a part can tell you a lot about its strengths and weaknesses. The best example currently is in Intel’s Core line of mobile processors. When examining the processor list you’ll notice that parts like the Core i5-2540M have TDP of 35W, while the Core i5-2557M has a 17W TDP.

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This tells you that the Core i5-2557M is designed to use less power than the Core i5-2540M. Since it’s based on the same architecture, this also means it will provide worse performance but better battery life. If you’re looking for a portable laptop, the Core i5-2557M would be better. If you care about performance, the Core i5-2540M is ideal.

Similar conclusions can be made from the TDPs of desktop parts. AMD’s latest Phenom II X4 980 Black Edition has a TDP of 125W, while (as mentoned above) the Core i5-2500 has a TDP of 95W. And what do you know – in benchmarks, it turns out the AMD X4 980 draws more power.

Conclusion

TDP is one of several important statistics that can help you hash out the performance and power efficiency of a new processor. While nothing can replace benchmarking, knowing a part’s TDP (as well as its architecture and clock speed) will help you make an educated guess about how a new part will perform.

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2 Comments -

Anonymous

It should be noted that while Intel CPUs have not quite reached the TDP of ARMs, the Atom Z6xx CPUs approach it with some having TDPs of 1.3W.

M.S. Smith

Really, they managed to get the Zs that low? That’s impressive.