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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PrinceGaz - Friday, April 16, 2004 - link
Interesting article, but I've a couple of suggestions :)If the fan on the heatsink was plugged into the motherboard used to test the CPU, you should instead run it off a dedicated stable regulated power source given an accurate known voltage. That totally isolates any effect the motherhoard, PSU load or anything else might have on HSF efficiency.
All current and future CPUs we're interested in have a heatspreader, which presumably does a decent job of spreading the heat over a fairly wide surface area compared to core-size of the processor (the AthlonXP/Duron line is effectively finished and won't concern enthusiasts, so their energy-consumption isn't too important). It seems a good way to translate recorded temperature over ambient temperature, into an actual power consumption in watts would be to make a little heater unit (with something like a heatspreader) you can mount the HSF on.
By adjusting the voltage applied to it and measuring the current you could take a whole range of readings covering a wide range of watts. You'd not only know whether the temperature difference rises linear with power, but also be able to give actual wattage figures for the CPUs. At least one site (whose name evades me) which does extensive HSF testing actually uses such a heater type system to compare HSF performance to ensure identical conditions.
From the results I must say I'm impressed with how well the Athlon 64 CPUs did, especially when running Prime95. Was Cool 'n Quiet enabled to reduce their speed in idle mode? If it was, I assume you did ensure with some utility they were operating at full speed while Prime95 was running? ;)
Prime95 is a great way to heat up processors but it may have a different impact on different CPU designs. The P4 runs it *FAR* faster than the AthlonXP does, or even the Athlon 64 despite the latter also having SSE2 instructions (which Prime95 uses). In particular have a look at the benchmarks page:
http://www.mersenne.org/bench.htm
and you'll see that for equivalent tests, the time taken by some different CPUs were:
Athlon XP 3200+ - 0.032, 0.066, 0.142
Athlon 64 3400+ - 0.025, 0.052, 0.116
Northwood 3.2GHz - 0.013, 0.026, 0.056
The Northwood 3.2GHz is running Prime95 roughly twice as fast as even the Athlon 64 3400+. Now while I can't say for sure that running it faster translates into more power-consumption, the fact that the test runs so much faster on that design makes the results difficult to trust. If however you've tried a whole bunch of different stress-test programs on the Athlon 64, Northwood and Prescott and found Prime95 gave the hottest temperatures on them all, thats fine. But if different tests give the hottest temperature for each design, then thats the one you should use for that design when carrying out future tests.
Sorry for rambling on so long, hope some of that made sense :)
CRAMITPAL - Friday, April 16, 2004 - link
http://www.theinquirer.net/?article=15374CRAMITPAL - Friday, April 16, 2004 - link
Obviously no one with a clue would buy a PressCrap when it clearly runs much hotter than the Northwood and is actually SLOWER in system performance. In InHell marketing speak that's called "90 nano performance". Sic !!! Now inHell is doing damage control after lower than expected profits and defective products they can't even deliver in quantity to Dull and WasteGate.Mumrik - Friday, April 16, 2004 - link
I meant an articles that claim the AXP only has a difference of 1Mumrik - Friday, April 16, 2004 - link
Doesn't seem very well done....How can we trust results that claim the AXP2500+ only have an idle/load temperature difference of 1 degree celcius?!
Pumpkinierre - Friday, April 16, 2004 - link
You didnt include the ambient air temp close to the fan (and fan speed- maximum or silent). Northwood temp range seems high. Cpu case temperature can be 10C under internal/diode temp.. 5C or so difference, both idle and load, between N'wood and Prescott is quite significant to an overclocker. The die size is approx. the same but given the 'missing 30 million transistors', 90nm and the large cache, the heat might be more localised on the Prescott affecting headroom. Good to see the a64 data. These AMD cpus seem to run cool.Voodoo80 - Friday, April 16, 2004 - link
What about cool and quiet? It's a pity this is not tested. I want to know what the idle temps would be if this is enabled.MAME - Friday, April 16, 2004 - link
Awww, I was hoping it'd be a heat nightmare and AMD would come to save the day!