CPU Heat Comparison: How Hot is Prescott?
by Derek Wilson on April 16, 2004 4:32 AM EST- Posted in
- CPUs
Final Words
From our data, it doesn't seem that Prescott is really that much hotter than Northwood. Like we mentioned earlier, though, heat output and our temperature measurements might not scale at the same rate. In other words, since Northwood is cooler than Prescott, our thermistor might be getting cooled even more by the fan. This could mean that Prescott and Northwood are even closer in total heat dissipation than in our temperature measurements. We are always working on ways to better collect this information, but hopefully what we have seen has been helpful.There is, of course, a temperature increase in Prescott though. But where did it come from? Prescott has about three times the number of transistors as Northwood (due to pipeline increases, the addition of 64bit functionality, and (not least) a doubling of the L2 cache). Prescott is fabbed on a 90 nanometer process rather than the 130 nanometer process of Northwood, which means that Prescott will have a higher power density.
There could also be some impact on increased temperature from Intel's new strained silicon technique. This increases the electron mobility through the body of a transistor. What this means is electrons move faster and transistors can switch on and off more quickly (something very good for high speed processors). Of course, this also means that transistors can end up leaking more current through them when they are off. This increases the power used by the chip which in turn increases heat output.
We asked Intel what (if any) effect actually using the 64bit extensions in Prescott would have on temperature, and we were told that it shouldn't have a significant impact on heat. Intel indicated that with the right 64bit application running we might see Prescott draw 2 or 3 more watts of power. Enabling and using the 64bit extensions will use parts of the chip that can currently remain happily disabled. Hopefully Intel will be right when they say that turning on this feature won't impact heat too much. Of course, we'll be there to test it out as soon as we can get ahold of a 64bit enabled chip.
We can't really be sure right now how much each of these factors affect Prescott's temperature, but all of them surely contribute.
The final issue we need to consider is the motherboard issue. Prescott is powered by a lower voltage than Northwood, but consumes more power. This means that it necessarily draws much more current. Though Intel did get the power requirements out to motherboard manufacturers, there may be some issues with Prescott support. Intel maintains that motherboards that were not designed for Prescott won't boot Prescott (and won't hurt either component), there sill may be some unforeseen issues, as even companies designing earlier P4 motherboards with an eye to Prescott wouldn't have had anything to test their motherboards with back when they shipped.
When it comes down to it, there are four options early P4 motherboards and Prescott. 1) Everything could work fine. 2) The system may not overclock very well. 3) The system may run but with reduced stability. 4) The system may not run at all. If there is enough interest, we may end up looking into Prescott and motherboard compatibility. Feel free to let us know if that would be something you would like to see.
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Etacovda - Saturday, April 17, 2004 - link
Yeah, id have to agree that the test was next to useless. The methods used were... archaic? to say the least. Put it this way, the AXP thats moved 1 deg under load generally should move in the region of 10 at least. so 1/10, applied to the prescott, would be a lot more... i know this method in itself is flawed ;) but thats the ghist of whats going on here.I hope you understand my point ;p
Pumpkinierre - Saturday, April 17, 2004 - link
#35 the heat capacity of air is small. If no heat sink were applied, MORE heat would be lost to the underside/mobo than the topside/heatspreader because the pins/traces/mobo act as a heatsink. Sure, if you place a liquid Helium 'cold finger' on the cpu you will get less heat loss from the underside but remember those metallic pins are linked to the heart of the die so thermal loss is inevitable. Slot 1/A would be better to cool (either side) but there would still be pin connection loss. If you replaced the die in the cpu packaging by a die size heating element with known power characteristics you might be able to produce a calibration curve in conjunction with fluid cooling or a temp. probe that would then be used to determine cpu power consumption. Of course, with the heating element measurements, the mobo is switched off with the cpu package/heating element sitting in the mobo sckt. I suspect Intel/AMD use a power flow determination as direct measurement is difficult.rwong48 - Saturday, April 17, 2004 - link
like someone else said, i was wondering on the accuracy of these temperatures because the xp 2500+ barton only increased 1ºC from idle to load..Coruscant - Friday, April 16, 2004 - link
If you provide a cold enough heat sink (not the typical heatsink, but a source that absorbs heat) then the heat transfer to that heat sink will override the transfer from the processor sides/bottom to the ambient air. Additionally, so long as the ambient conditions are maintained, it would be reasonable to assume that the heat loss to through those surfaces would be comparable. Of course, assuming the surface temperature of all the processors in question are maintained at a pre-defined setpoint, the heat transfer from the processors to ambient would largely be the same, varying only by the difference in exposed surface area. Again, this would all be in the pursuit of determining at what rate of heat is generated be the various processors.MoronBasher - Friday, April 16, 2004 - link
*unless i am wrong and they did enable cnqbut the review wasn't that good altogether.
MoronBasher - Friday, April 16, 2004 - link
the article was missing something. they should have used the diode along with the probe. also, they should have used cool n' quiet for the athlon64 as that would be what is actually going on in real world terms.just my 2 cents
mechBgon - Friday, April 16, 2004 - link
The "percent increase" graph should be using Kelvins as a basis, not Celcius.For example, let's say a processor idles at 40°C and rises to 60°C under load. That's an increase of 20 Kelvins, or 20°C if you prefer, but it isn't a 50% increase... 40°C is 313 Kelvins, so a 20° rise is 20/313 or 6.4%.
AIWGuru - Friday, April 16, 2004 - link
The methodology used in this "test" wouldn't pass muster in a grade 4 science class.I can't believe that ANYONE is THIS inept.
This article leaves me thinking that someone at Intel paid someone to write it.
ZobarStyl - Friday, April 16, 2004 - link
p.s. Not that I own one of those hunks of junk, but let's be honest that's where intel gets its cash, not from the enthusiast market.ZobarStyl - Friday, April 16, 2004 - link
I would like to see a closed-case standard (same case and components, diff proc/mobo) with the internal case ambient being measured in different places. If Prescott is such a current hog, then (as was mentioned in relationship to electrical resistance above) other components such as the PSU might start adding heat to the total system. I don't run all these 80mm's to keep just the processor cool; I run them to keep all my components cool and keep system life at an optimum. If Prescott under load is 50 degrees but the sum of its output makes my case 15 Celsius hotter, then no amount of CPU speed will make me want to buy that. A processor is just one part of the system, albeit the most important, but that doesn't mean I want to buy every other component in my system twice because of premature thermal breakdown.Every computer case is a thermodynamic system straight out of a Physics textbook. Just because one component makes 10 degrees more heat doesn't necessarily mean the whole system can dissipate all that heat, and BTX aside Intel is going to have some serious issues running these things in major manufacturer style cases. I mean when the best cooling setup you get with a Dell is a single 80mm, and their smaller ones have no case fans at all, the Prescott is going spell early death for a lot of these systems.