CPU Heat Comparison: How Hot is Prescott?by Derek Wilson on April 16, 2004 4:32 AM EST
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Final WordsFrom 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.