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Deep UnderVolt/Clock: 4.7W CPU PC

A reader’s account of the most extreme undervolted and underclocked system I’ve yet heard about. Mark Charlesworth created an auto-speed adjusting AMD XP1700+ system that runs with as little as 4.7W CPU power draw yet ramps up to full speed when needed. Read how he did it!

June 3, 2004 by Mark Charlesworth

Here is a detailed reader’s account of the most extreme undervolted and underclocked system I’ve yet heard about. Mark used the resources available here at SPCR and a few other tools from research elsewhere on the web to create an auto-speed adjusting PC that runs with as little as 4.7W CPU power. Surely that allows for an extremely quiet system! Read how he did it.

— Mike Chin, Editor

I thought the deep underclock/undervolt that I have managed without too much effort might be of interest. I have my Athlon XP1700+ at 1.1 V and 300 Mhz as opposed to 1.6 V and 1466 MHz default values. The calculator CPU Power by Kostik in SPCR’s software web links suggests that at these settings, the CPU is using 4.7 Watts as opposed to 49.4 Watts at default values, a 90% improvement.

Here is how I did it.

First of all inspired by CPU Undervolting & Underclocking: A Primer and Undervolting T’Bred-B CPUs with José Ángel, I reduced the CPU to 1.275V and Chipset to 1.4V in BIOS at standard speed settings. The 1.275V CPU voltage (VCore) is the lowest that the PC will boot at reliably from cold . I used Speedfan (also available in SPCR’s Web Links) to check temperatures and fan speeds, and then reduce the fan speeds. I ran the computer like this for a month or so, as I was busy with other things.

When I had more time, I started to experiment with underclocking. The PC will reliably boot at a 5x CPU multiplier set in the BIOS and I then used 8rdavcore (see Web Links again) to see if I could reduce VCore further. I found that when the machine has already booted at a 5x CPU multiplier, I can open 8rdavcore and move the VCore slider straight from 1.275V to 1.1V and apply the change without any intermediate steps.

Finally I used the 8rdavcore AutoFSB function to let the Front Side Bus (FSB) drop from 133MHz default to 60MHz when I am using Word, etc . If I am playing games such as Neverwinter Nights, I leave the FSB at 133MHz and if I want to play recent FPS games, etc I change the CPU multiplier back to the 11x default value in BIOS.

Many XPs can be also be overclocked and overvolted easily for quite a gain in performance (I have not tried settings above default). It would be interesting to know if Mobile XPs, Athlon 64s and Intel CPUs can provide such a wide range of performance and energy consumption. This consumption appears little more than VIA CPUs. [Editor’s Note: Actually less than most of the current stock-clock VIA.]

As well as the energy and noise savings this allowed, it also let the northbridge and southbridge of the motherboard run much cooler. I did not have problems with stability before and nearly all sound problems were fixed with q242937.exe (See the NForce Audio FAQ at NForceHQ.) ) but I am still happier running at these temperatures.

The memory is at the default 2.6V and the video card is at the default 1.5V.

So there we have it, an XP1700 running at 300MHz and 1.1V and the loudest thing is the power supply fan . Indeed this system might consume less energy than the old Pentium II 300MHz laptop I used to use.


The original system was supplied by Kool’ ‘n’ Quiet (UK). Current system specifications are:

– AMD Athlon XP1700+ Thoroughbred, B0 core stepping. Fitted with a Zalman CNPS5100-AlCu CPU cooler and a resistive cable to lower fan speed. The CPU and case fans are connected together to ‘CPUFAN1’ connector on the motherboard with a splitter and speed controlled in Windows via Speedfan or 8rdavcore. If I was to build now I would probably fit a cooler with better passive cooling and a quieter fan (Perhaps a Nexus AXP-3200). However at low speed (1800rpm) the fan is almost inaudible.
– ABIT NF7-S V1.2 Motherboard, 2.3 Bios, Zalman ZM-NB32J passive northbridge heatsink, MicroCool southbridge heatsink (southbridge cooler is probably not necessary now with reduced chipset voltages).
– 2x256MB PC2700 RAM – Nanya NT256D64S88ABG-6.
– 3D 6015 Radeon 9000 VGA card with Akasa DFS401012M 40x40x10mm fan replacing standard ATI fan. This 3-wire fan is speed controlled in Windows via Speedfan or 8rdavcore and connection to the ‘CHAFAN1’ connector on the motherboard. It is quieter and cools better than the standard ATI fan. This was an easy mod to do, simply requiring the fixing holes on the Asaka fan to be more deeply counter-bored to allow the original screws to be used. VGA card underclocked with RivaTuner.
– Windows 98SE
– Compucase 6A ATX case with 120mm exhaust fan connected to ‘CPUFAN1’ and speed controlled via windows (see Processor specifications above for details)
– Heroichi HEC-300AR-PT PSU. According the manufacture’s specifications, this is reasonably efficient (68% minimum 72% Typical). With all the other fans at minimum speed this is the loudest thing in the PC. May swap it at some point (Perhaps an Enermax NoiseTaker or something based on Multi-Resonant-Topology (http://www.nv-power.com/co_6182.htm) which may be up to 90% efficient).
– Seagate Barracuda IV 7200 rpm 80GB HDD
– Plextor Plexcombo 20/10/40-12A
– Philips 2x2x6 CDRW
– NEC LCD1501 Monitor. The lowest energy monitor I could find at 20Watts Max and <2Watts standby.

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