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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TrogdorJW - Friday, April 16, 2004 - link
AMDscooter, regardless of the fact that you might run a P4 rig, any accusations such as yours ("Speaking of stoopid. Intel must have floated him a good size check to write this article saying the Prescott is not much hotter than the Northwood. The whole article reeks of Intel PR hard at work...") are hard to view as anything but you just being an ass. Do you have any real evidence that Anandtech is getting paid by Intel to provide higher scores? No. Must be pretty comfy taking pot shots from the cheap seats, though.There's a major difference between pointing out the flaws in an article in a polite manner (i.e. I don't think your testing methodology is good because....) and just flaming away like a fourteen-year old that needs more Ritalin. Is the article flawed? Undoubtably. But short of spending a shload of time and doing enough work for a master's thesis in thermodynamics, you wouldn't expect perfect results.
By no means are the results given in the article portrayed as accurate. The entire tone of the article is basically one of, "Well, this is what we did and these are our results, but we're not really sure if they're good or not." Clearly, the response is that the results aren't exactly meaningful. Fine. Now try and be helpful in how to correct the tests (like PriceGaz, for instance) instead of being rude.
You act as though you're paying AT money for the articles they post. I figure the amount of ad revenue generated by the visits of one person in a month amounts to a few cents at most. Please try to make your two cents' opinion count in the future, instead of squandering it on insults.
For the record, I also read THG regularly, along with Ars Technica, HardOCP, Firing Squad, and various other sites. I would wager that *none* of them receive money from Intel or AMD in order to get a better review. Money for ad space? Sure. Free product to review? Probably. But I've seen every one of these sites rip on both Intel and AMD products at various times, so just get off your high-horse and contribute, people.
Pumpkinierre - Friday, April 16, 2004 - link
If you use a coolant, you still only get the heat emitted from the top half of the cpu unless you had a fully enclosed 'Powerleap' type water bath adaptor- difficult. The only other way is to measure power in and power out on the all the pins. Possible but difficult and it doesnt allow for calculation energy consumption but this I suspect would be minute cf to heat production in a cpu. These methods also dont identify heat localisation in a cpu which is just as important and limiting. In the case of Prescott with its 90nm, switched off 64bit and large L2, I would suspect this is a real problem ie hot and localised. So even though derek's methodology is crude, its still a reasonable stab at a difficult problem.mindless1 - Friday, April 16, 2004 - link
It was disappointing that bus disconnect wasn't enabled on the Athlon, so it was quite a dissimilar comparision at IDLE.The article has one conclusion quite backwards-
"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."
If the Prescott is heating up the heatsink more, there's a greater difference between it and ambient, the same fan, flow-rate, is more effectively cooling the hotter CPU. A 1C temp difference in the heatsink corresponds to a larger difference in the CPU.
jojo4u - Friday, April 16, 2004 - link
I'am disappointed that you did not enable the disconnect on the Athlon XP and Duron platform. That would place the Ahtlons much better. I am also interested wether Cool'n'Quiet has been enabled.eetnoyer - Friday, April 16, 2004 - link
I think a good way to approximate thermal dissipation would be to have a normal water cooling setup with everything insulated except the radiator. The only addition would be a flow diverter to swith between the radiator and a bypass. When the system reaches temperature equilibrium (most easily measured by a simple thermal probe in the reservoir) swith from the radiator to the bypass. Measure the temperature over a given amount of time or until a specific temperature is reached. You could easily compare processors against one another. Or, if you know the precise amount of water in the system (not including the radiator loop), you could calculate heat output for each processor.Phiro - Friday, April 16, 2004 - link
Anandtech: Good article, you did your best to sort through a apples to oranges to bananas to grapes type of situation.From the way people talked I expected huge heat differences and this has altered my outlook on Prescott abit. Thanks again.
tyski - Friday, April 16, 2004 - link
I would also like to see some sort of measurement involving the mass flow rate across the processor and a the temperature at inlet and outlet. Having also suffered through thermo hell, Derek's method reeks of uncontrolled outside factors, such as the case temp affecting the cooling rate of the fan and the heat transfer of the heatsink to the outside air. Temperature != power and power is what I think everybody here is interested in.theobscure - Friday, April 16, 2004 - link
a better way to test the heat generated by the processor would be to construct walls on all 4 sides of the processor, and then fill them with a known amount of water, then run the processor for a set amount of time and measure the change in temperature of the wath bath.CruisinGT - Friday, April 16, 2004 - link
In regards to the author's last statement, I would love to see a Prescott and motherboard compatibility article particularly on the first i875 motherboards released like the AOpen AX4C Max and the original Abit IC7s!! Thanks.AnonymouseUser - Friday, April 16, 2004 - link
"Boy, some of you guys are cruel assholes and belong in Tomshardware and not in anandtech with your attitudes."Uh, not! If they did belong at THG, they would have eaten this up as "The Gospel". Generally speaking, Anandtech readers can spot bullsh!t better than THG readers, and I have to agree that this article seems to have a whole lot of "Intel Inside"...