I really cant understand TDP

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MrCasualGamer

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Jun 29, 2014
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I googled a lot, read wikipedia etc, but I am still confused.

Wikipedia says:"The thermal design power (TDP), sometimes called thermal design point, refers to the maximum amount of heat generated by the CPU, which the cooling system in a computer is required to dissipate in typical operation."

intel ark says "Max TDP

Thermal Design Power (TDP) represents the near maximum power a product can draw for a thermally significant period while running commercially available software. For thermal solution requirements please consult the Datasheet, volume 1 "

I could not find Datasheet vol 1..



Can someone please teach me TDP in simple terms?


My problem or understanding is somewhat this way from above reads..

Say CPU A has TDP of 100 Watt and CPU B has TDP of 50 Watt

So can I simply consider that CPU A will need a 100 watt fan to cool it under normal load and CPU B will need a smaller 50 Watt fan to cool it down under normal mode? ..

how much watt does the stock cpu fan use? say for latest intel i7 4790k box cpu the max TDP is 88W.. so the included fan should be drawing around 90W at max rpm from my PSU? ..

thanks.
 
Solution
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It means cpu A will chew through 100W whereas cpu B will only chew through 50W. Not how much fan power you will need.

A stock cpu fan uses say 10W. But it blows air over a cooler that gets rid of say 100W of heat.
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MrCasualGamer

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Ok, I am somewhat getting it now .. One more question ..

How do I apply the TDP knowledge to building a system? Say I want to use the above CPU .. I7 4790k which has max TDP of 88W .. Now how do I use this information to decide what cooling is needed? Or what is the use of this information ?
 
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i7Baby

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It's not much to worry about for building. eg a pc with a GTX760 needs a 500W PSU. Why? Because someone else has worked it out and tested this stuff for you. You can use Power Calculators if you want eg http://extreme.outervision.com/psucalculatorlite.jsp
or you can just look for a database eg http://www.realhardtechx.com/index_archivos/Page362.htm

Or you can go through finding the power consumption for every bit in your pc and add them all up. I've done all this and realise that looking at the database is pretty well all you need unless there's something odd about your pc.
 
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MrCasualGamer

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Thanks so much man .. I think Now I get it .. see if i am right

Cpu A .. desktop cpu TPD 100 W
Cpu B... mobile CPU TPD 5 W

Cpu A is going to produce more heat and would need some kind of fan, to dissipate that heat ..
and CPU B TDP 5 W .. is going to produce such low heat that even a fixed heatsink would be adequate..

is this now somewhat correct? it kind of considers the thermal part of it to practically apply it to cooling?
 
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bmacsys

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You have it all wrong. What it means is that the heat sink fan is designed to cool a processor with a TDP of 65 watts. That heatsink fan won't be able to adequately cool a processor of 100 watt TDP which runs hotter than a processor of 65 TDP. An analogy is a small air conditioner can't cool a large room.
 
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DelroyMonjo

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Engineers make a nice living figuring this stuff out for us dummies, MrCasualGamer.

The amount of heat that a substance absorbs is connected to its temperature change via its molar specific heat c, defined to be the amount of heat required to change the temperature of 1 mole of the substance by 1 K. In other words, c is the constant of proportionality relating the heat absorbed (d′Q) to the temperature change (dT) according to d′Q = nc dT, where n is the number of moles. For example, it takes approximately 1 calorie of heat to increase the temperature of 1 gram of water by 1 K. Since there are 18 grams of water in 1 mole, the molar heat capacity of water is 18 calories per K, or about 75 joules per K. The total heat capacity C for n moles is defined by C = nc.

Now, instead of water, a heatsink uses copper and radiator fins with a specific area to spread the heat, blah, blah, blah....
 
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