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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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:http://www.crystalfontz.com/forum/showthread.php?s...
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.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?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.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.