Undervolting T'Bred-B CPUs with José Ángel

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August 8, 2003 by José Ángel Domínguez (jdomsan at infonegocio.com)

This article by José Ángel Domínguez spells out just how wonderfully "underclockable" certain AMD Athlon Thoroughbred XP cores are, and what that means for cooling and noise. Combined with the unlocked state of all the Thoroughbred cores we're aware of, these inexpensive CPUs make for an excellent basis for very quietly running computers. José, a first-time contributer to SPCR, on the verge of obtaining his telecommunications engineering degree at the University of Valladolid in Spain. He loves computing and hates the noise normally associated with it.

- Mike Chin, Editor / Publisher, SPCR

My Quest for a Silent PC so far

Being a computer enthusiast usually means testing and buying faster, newer components. But it also means buying hotter components, and then, out of neccessity, better cooling. Better cooling, if done cheaply, means faster, noisier fans. This is the way that PC noise has become an important element to be taken into consideration for me.

If you spend many hours a day in front of your computer, a typical way to "dampen" your PC noise is adding more "noise", eg. music, radio, etc, until it starts disturbing the people you live with.

That's what happened to me, and that was the day when I started searching through the Internet for a solution. So I typed "Silent-PC" in Google, and reached The Silent PC (http://home.swipnet.se/tr/silence.html), a collection of all kinds of information about this. It was very useful for a beginner.

Through The Silent PC, I found and began subscribing to the Yahoo Silent-PC Mailing list. That was the real beginning of my silencing quest. A lot of users were having the same wonderings, and were solving them successfully. But that was 20 months ago -- there was no silentpcreview.com at that time :-).

During this time I learned very useful tricks and mods from the most active members of that list; one of them was Mike Chin. For example, the first mod I did that reduced my computer noise a lot was free, no new components were necessary: it was relocating the thermistor of my Enermax PSU to a cooler place, thanks to a self-explanatory photo sent by Mike to the list. That photo is now in his article Quieting the Enermax & other themistor fan PSUs in the Power Supplies Section.

My Experiencies with Undervolting (and Underclocking) CPUs


DISCLAIMER & WARNING: While the procedures described here have been successfully completed by me, I take no responsibility for your property and your data. The information is provided here in good faith; what you do with this information is your responsibility. I recommend you study the article carefully and take all necessary precautions to protect your data, as this can be at risk when the CPU is not provided with sufficient voltage for its operation (what we try to demonstrate is that "sufficient" is well below its default). These procedures should not damage your CPU, motherboard or PSU (on the contrary, their load should reduce and thus extend longevity), but if they do, I repeat, I take no responsibility.

(Also, this article assumes that names of Athlon XP CPU cores are familiar to you, and you are able to distinguish them. If that's not the case, you can check related info for example in this Techboard tutorial and also here: http://8rdafaq.com/file.php?file=cpu_info.htm.)


I was shocked when I first saw Mike's original article CPU Undervolting & Underclocking: A Primer (in the General Section). Reading that an Athlon 1Ghz can work at 600Mhz with only 1.17V is rather impressive.

Something that must be always considered in silent systems is power consumption. The less, the better, and easier to cool quietly. Another important consideration is that power consumption gets reduced by voltage not in a linear way (as does with frequency), but by its a squared. So undervolting is much more dramatic in reducing power than lowering the clock frequency.

So I started trying to undervolt. I had an Epox 8KTA3 with Palomino XP 1700+. All that motherboard could undervolt was -0.1V from the default CPU voltage. I tried it, and worked fine. It reduced max. power consumption from 64W to 57W, enough to lower temperature by 2º or 3º C, or allow the fan speed to be reduced 200~300 rpm to maintain the same temperature. Not much, but a little step in the right direction.

Then I bought an Abit KX333-R, a motherboard that can set voltage as low as 1.1V (see more Undervoltable Motherboards in the Recommended Section), but I found that the undervolt limit of my CPU was near what was set with the 8KTA3. And this Palomino XP was multiplier locked. Unlocking it is not as easy as it was in pencil trick Thunderbird days.

Next Step: A Thoroughbred B 1700+

I found one with JIUCB stepping. Its default settings are 1467 MHz clock speed,1.6V voltage, and 56W max power consumption with that settings. Like all Thoroughbreds so far, it is multiplier unlocked. Undervolting with this CPU was much improved. With the Thoroughbred, I achieved the following stable speeds.

Speed (MHz)
CPU Voltage (V)
Max. Power Consumption
Typical Power consumption
733
1.15
17W
14W
800
1.18
19W
15W
933
1.18
22W
18W
1000
1.20
24W
19W
1066
1.20
25W
20W
1200
1.20
27W
22W
1333
1.20
30W
24w
1400
1.20
31W
25W
1466*
1.25
34W
27W
1533
1.28
37W
30W
1600
1.33
41W
33W
1667
1.40
47W
38W

* Default clock speed

The same speed could be reached with only a little more that the half of its original power consumption! (34W / 56W = 60%). You can imagine what this means for reducing cooling fan speeds -- and the associated drop in noise!

Time went by and I began reading in many forums about new Thoroughbred steppings that overclock further. If they overclock further without increasing voltage significantly, thinking about this logically, maybe they can run at a voltage much below their default. So next step is to get one of those steppings.

I got lucky at my usual computer shop one day: I managed to get a Thoroughbred B 1800+, JIUHB stepping, 1.5V default voltage (51W max power consumption with that settings). I rushed to check if my logic was right. With this JIUHB 1800+, I obtained the following stable speeds.

Speed (MHz)
CPU Voltage (V)
Max. Power Consumption
Typical Power consumption
733
1.13
16W
13W
800
1.13
18W
14W
866
1.13
19W
15W
933
1.13
20W
16W
1000
1.13
21W
17W
1066
1.13
22W
18W
1133
1.15
24W
19W
1200
1.15
25W
20W
1266
1.18
28W
22W
1333
1.18
29W
23W
1400
1.20
30W
25W
1466
1.20
33W
25W
1533*
1.23
34W
27W
1600
1.25
36W
29W
1667
1.30
40W
32W

* Default clock speed

And that how it ends. You may ask if these results are easily reproducible. A lot of factors can affect the results, but if you happen to own a good power supply and a good motherboard, yes, you can reproduce them. Most CPUs with these steppings should work with these voltages +/- 0.05V.

I have briefly tested other CPUs identical in steppings to these two samples, and the results were similar if not identical. I have also tested quickly a T-bred-B 1700+ JIUHB, 1.6V, and the results were in-between the two CPUs shown here.



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