Comment by adrian_b | Hacker News Reader

Comment by adrian_b | Hacker News Reader

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The TDP (thermal design power) is the maximum power consumption in steady-state conditions, when all the CPU cores and/or the GPU are 100% busy and the power consumption is limited to avoid overheating. It is used to dimension the cooling system, together with the maximum working temperature of the CPU.

The TDP has nothing to do with the battery lifetime in normal usage. Any smartphone or laptop will drain completely its battery in a couple of hours at most when running at the power limit (you will never see a laptop configured for an 8 W TDP also having a 99 Wh battery; such batteries are normally used for laptops where the CPU is configured for a 45 W TDP).

For the battery lifetime what matters most is the power consumption when the CPU is idle (which should be a fraction of a watt, so that the total idle power consumption is dominated by the display power consumption) and also how big is the additional power consumption caused by light CPU loads, like Internet browsing, movie watching, document reading and editing etc.

I had a feeling TDP was not the correct concept here, alas it's too late for editing, but the point still stands.

Appolagies for the confusion.

As for where I got my 8W figure from:

> All of the chips except for the Core Ultra 9 default to 17 W base power, with a minimum of 8 W (if the manufacturer configures it that way) and a maximum Turbo Boost power of 37 W.

anyone that has tried building a gaming PC based on intel's supposed TDP number on the chip spec sheet would with TDP being a

reported TDP: 125W

actual power usage: 350w

When the actual power used by the CPU reaches 350 W, that happens because the BIOS of the motherboard configures the CPU for an unlimited power consumption.

In this case the CPU consumes as much it can before the temperature exceeds the temperature limit. The actual power that is consumed will be determined by how good is the used cooler.

The MB manufacturers do this so that their motherboards will win the benchmarks in published product reviews.

Unless the BIOS locks the power control registers, you can configure any Intel or AMD CPU for any power limit you desire and the power consumption will never exceed the set limit.

A low power limit will diminish the achievable multithreaded performance, but unless the limit is very low the multithreaded performance per watt will be greatly improved.

The TDP matters a lot for a laptop or for a SFF computer. In this case the laptop or small computer is really designed for a definite TDP, e.g. for 28 W or for 45 W, and attempting to make the CPU consume more than that will result in thermal throttling.

For a desktop, the design of a motherboard does not depend on the TDP, because it does not include the cooling system. The MB designer only takes care that the voltage regulator should provide enough current to reach the highest power consumptions that will not destroy the CPU.

The actual power consumption that can be reached without thermal throttling is determined by the case, the case fans and whatever CPU cooler is used. For most desktops it is easy to ensure that the CPU can consume more than its nominal TDP, without overheating.

Does this mean that Minimum TDP = maximum power consumption* at the CPU's lowest power configuration?

* Averaged over some time window relevant for cooling

Yes, that's correct as long as you don't worry about transient boosts like PL1/2!

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