There are plenty of issues with current methods of comparing temperature data between processors, and we have been hard at work trying to come up with something that gives us better and more comparable results than the temperature data reported by different processors' thermal diodes. In considering different approaches, we have run into the same problem over and over: how do we measure the total heat output of the processor in any nearly accurate way.

The problem with thermal diodes is that between different architectures, there isn't really a way to compare what is being reported. The diodes only measure the temperature at a specific location, and the number we can pull out of a processor isn't necessarily representative of the average temperature of its surface.

Measuring the temperature increase of the system itself has issues as well. Different components in a computer heat up as well, and there's no way to really isolate the contribution of the processor itself to this process. The only number that can truly be compared between processors is the total energy output by the surface of the chip (or heat spreader).

The heat transfer from the CPU to the outside world would be a wonderful number to have, but there is the unfortunate necessity of a heatsink and fan for modern processors to run without cooking themselves. There isn't really a way for us to get to the surface of a chip in order to measure anything. So how are we supposed to measure how hot something is getting when we are required to be cooling it at the same time?

Well, there isn't any easy way we can think of, but just because something is impossible doesn't mean the AnandTech staff can't get it done.
Heatsink Modding: The New Rage


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  • AMDScooter - Friday, April 16, 2004 - link

    Quote:"Boy, some of you guys are cruel assholes and belong in Tomshardware and not in anandtech with your attitudes."

    Most of us here are not mindless zealots who believe everything we read. We post what we feel are valid rebuttals to an article, so we are asshoels now..?? Whatever. At the very LEAST the article is a bit misleading. I can see no other point to the article other than getting uninformed peeps like Icewind to buy Prescotts... My2c.

    BTW, dont mistake my name for bias. I currently run a 3.2c in a Vapo unit and am very happy with it.
  • steller2k - Friday, April 16, 2004 - link

    Having some background in thermodynamics, electrical theory and computers (The Navy slang term was Nuc Electrician). It occurs to me that the Prescott processor itself may not be much hotter than the Northwood. The lower voltages would lower the losses in the die reducing the amount of heat there, offset by the increased current requirements and increased losses due to the closer proximity of the transitors, hence roughly the same performance. The biggest problem as I understand it is the motherboards themselves overheating. The term is I^2R losses, as current increases the actual heat generated in other power supply and motherboard components are squared, or in other words if current requirements are doubled the heat produced is four times the original amounts. Don't get me wrong, I really like Anandtech and I found this article surprising and informative; I didn't expect the temperatures on the Prescott and Northwood to be that similar. But I think in the future that for a clearer picture of total heat cost of a processor should include measurement of the the ambient case temperatures. An interesting side note: the higher temperatures of the P4s helps them to dissapate more heat than the lower temperatures of the Athlons, of course that only works up to the point that the rest of the computer doesn't melt. ;) I'm trying to think of a few ways to measure the true heat cost of a certain set of components, but most of what I'm thinking would require some significant mods or a custom/purpose built case. (Like the heater used for heatsink testing mentioned above).

    Relatively happy owner of an AMD Athlon 64 FX, if only there were some worthwhile apps and Socket939 had been a launch item... <sigh>
  • AnonymousPutterer - Friday, April 16, 2004 - link

    Crouscant, you might like to see some notes on my rather sloppy DIY rig, featuring precisely measured flow rates and temps before and after:
  • TauCeti - Friday, April 16, 2004 - link

    I just don't get what the author of this article wanted to measure. Was it the temperature of the die in combination with a specific cooler?

    If it was about _heat output_, why not just measuring the power 'usage' of the CPU? I think about 100% of the 'used' electrical energy is converted to thermal heat _inside_ the case because it does not look like the CPU radiates HF-waves and induces heat _outside_ the case?!

    I just don't get it.
  • klah - Friday, April 16, 2004 - link

    Add another graph showing the idle temps of the A64 with C'n'Q enabled.

  • Icewind - Friday, April 16, 2004 - link

    Boy, some of you guys are cruel assholes and belong in Tomshardware and not in anandtech with your attitudes. Reply
  • Sahrin - Friday, April 16, 2004 - link

    Pardon my lack of a degree in thermodynamics, but isn't there a significant difference between heat dissipated and temperature? We were shown that the effectiveness of heat distribution negatively impacted the XP's quite significantly (and this is further supported by the fact that they didn't increase percentage-wise in temperature anywhere near as much as the heatspreader processors did)...aren't there possibly other factors here? Intel said the TDP for Northwood was...what, 89 as I recally? And TDP (this is an average, not a maximum) for the Prescott is 103W, and it is speculated that Prescott at times will dissipate as much as 130W? Isn't this what is important...? (I may just be running in circles here) The amount of heat put out into the volume of the case...the heat doesn't just disappear, it fills the volume of the case and then is blown out (or ideally, is blown out before it has a chance to dissipate within the case)...this is the reason for the BTX standard, new huge coolers the LGA etc. etc. etc. Right? Reply
  • AMDScooter - Friday, April 16, 2004 - link

    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. WTF kind of testing methodology is his temp probe in a heatsink BS?? All the chips he tested have an on die temp sensor, but he takes all his readings from a hole drilled in the heatsink?? What a load of bunk. I thought Anand had finally grown up as he has not written an article this biased in some time. For a few minutes there I thought I had accidently stumbled onto Tom's site. So at this point our choices are to believe the rest of the world(myself included) and forum members all over in saying the Prescott is hot as h3ll or.... believe Anand and run out and buy a cool running 3.2E.... and watch it melt our MOBO's. Reply
  • Jeff7181 - Friday, April 16, 2004 - link

    Whew... glad... I thought I might have been the only one who read this and thought "huh?"

    This doesn't appear to be your best work, Derek.
  • Coruscant - Friday, April 16, 2004 - link

    Maybe some suggestions on how to better measure the heat load of the processors. Providing a mass flowrate of coolant across the processor sufficient to cool the processors to a set temperature, and with the coolant having a known inlet temperature condition, measuring the outlet temperature would provide a reasonably accurate measurement of the heat generated. Considering how commonplace liquid cooling has become, certainly this setup wouldn't be out of the question. All that would be required would be a refrigeration loop, adequately insulated coolant reservoir, variable speed pump, and several (3) thermistors. Just a suggestion, from a mechanical/process engineer. Reply

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