Reducing heat generation by reducing VCore and frequency

[Steerpike]

Mike C made a comment in a recent post about lowering VCore to reduce heat. I've just bought an Asus P4B533, with P4 Northwood 1.6 Ghz, but the bios setup does not seem to allow for reducing VCore below 1.5V. Is this possible with this mobo? (I read the article in Mods/Projects about silencing a P4 system, but no mention of reducing VCore).
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<BR>I've been reading a lot about laptops and intel's 'speedstep' technology, which reduces the chip speed in battery mode to extend battery life. If this works for laptops and batteries, then logic would suggest that it should work for desktops and heat/noise.
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<BR>While I may occasionally use my system for heavy duty work (video compression, etc), it spends 95% of it's time either idle, editing emails, or routing internet traffic to my other PCs. So - I'd be more than happy to drop my 1.6 GHz cpu to 800MHz or thereabouts!
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<BR>How practical is this? I tried to reduce the FSB on my 'test' system (a throwaway Athlon 800 system that I picked up for $200 from a friend) but I could not get it down less than 90MHz (from it's default of 100MHz). When I selected 66MHz, the system would not boot.
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<BR>I've bought a DigitalDoc5 to measure temps and control fans, and I'd be happy to have fan noise on the odd occasion when I stress the system.
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<BR>So how about it - can you seriously underclock a desktop PC, and by doing so, do you really lower heat?
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[addsig]

[MikeC]

I have to admit I made no attemp to underclock the P4-1.6A because there was no need. It runs virtually inaudibly even overclocked to 2 - 2.1G at stock Vcore with the stock Intel HS (or any number of other better HS) and Panaflo 80mm L at ~5-7V.
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<br>As I type, the P4 is running at 2.13 GHz with a Zalman 6500B-Cu HS & Panaflo 80mm L at 5V. The room temp is ~24C, the case temp is ~30C, and the CPU temp is 43C. No problems; even under high loads, it never hits 60C, which is perfectly safe with any CPU if you are reading the core diode (as you are with P4s). Besides, all the thermal protection features of the P4 makes it almost impossible to damage by overheating.
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<br>You CAN dramatically change heat generation with underclocking / undervolting, but unlocking the multiplier is very helpful if you want to go to extremes.
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<br>The best underclocking/undervolting results I've had is with a pencil-unlocked 1GHz AMD T-bird. Set to 665 (133 x 5) MHz & underclocked to 1.25V (down from 1.7V) the CPU temp dropped over 10C:
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<br>Ambient - 22C
<br>HSF: Swiftech MC462 + Panaflo fan at 5V
<br>@1 GHz (10 x 1000): ~46-47C typical
<br>@665 MHz & 1.25Vcore: ~35C typical
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<br>The stock wattage is ~48-49W. With my settings, it dropped to ~18W.
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<br>I didn't actually run it at this state for long because it was normally set to 865 MHz (133 x 6.5) and 1.45V, and temps were ~42C with a Swiftech MC462 + Panaflo at 5V. Same noise level (virtually silent), cool enough, better performance...
[addsig]