Guide: How To Undervolt Your Dothan CPU

[i game with a gateway]

I thought anandtech could use this and I did a search and there were no guides here. I posted this over at www.notebookpictures.com also.

Why should you undervolt?
Well, undervolting your mobile cpu will give you more batttery life as it draws less power, reduce heat and noise since there isn't as much heat generated, and overall, the same performance you would get if you didn't undervolt, so it's beneficial.

First, you will need to download Notebook Hardware Control available here:
http://www.pbus-167.com/chc.htm#anchor_download

also Prime95 available here:
http://majorgeeks.com/Prime95_d4363.html

NHC (Notebook Hardware Control) will be the program used to change your voltage. It also displays temperature, CPU speed, and hard drive information. Prime95 will be used to make sure that it your undervolt is 100% stable.

First, install NHC. Then, Prime95. Open Prime95 and make sure you are "torture testing" your CPU in the background while we are adjusting voltages. If you undervolt too low, the test will automatically fail and notify you via the task bar.

Next, while Prime95 is still running in the background with your CPU at 100%, open NHC. Click the "CPU Speed" tab and change AC power (assuming you're plugged in) to dynamic switching. You can also, as I have, switch the Battery power setting to dynamic switching also. Click the "Enable custom dynamic switching" check box and also the "Switch only between min. and max. Multipliers" check box. The settings I use are for both AC and Battery:
Min. Load: 70%
Max. Load: 80%

My min. multiplier is 6x and max. is 16x. This means that when the CPU is running at 0-69%, it is running at min. multiplier to conserve power. When it's using over 80% CPU usage, it's using the max. multiplier, hence boosting power consumption and heat.

Now that we have or CPU speed settings set, we'll move onto the undervolting. Move over to the "CPU Voltage" tab. Check the 6x multiplier box and the 16x multiplier box. This now allows us to change the voltage for the min. and max. multiplier. Make sure Prime95 is still running. For the 6x multiplier, change the voltage to 0.700V and click "set". It will now run at that voltage and multiplier to make sure everything is all right. It takes 30 seconds to do this. If it passes, that's great and now your when your min. multiplier is used, e.g. when CPU usage is 0-69%, it will be running at 0.700V. Also note that Dothans vary in clock speed so your lowest setting might be 800MHz and the voltage setting will be higher than 0.700V.

Moving on to the more important max. multiplier, 16x, this is where Prime95 really comes in handy. For my 1.6GHz Pentium M, 1.020V is as low as I can go with Prime95 stable. So, you will have to experiment as it will vary. Just slowly lower it from the stock voltage, with Prime95 running, until you hit a voltage that Prime95 fails on. I have found that 1.036 is a good spot, so you might want to try that. Keep testing the voltage. If you just changed to to a lower voltage, let Prime95 run it for awhile to make sure it's stable. If it fails, up the voltage a little and make sure that's stable.

This concludes the guide, and now your Dothan CPU will be running cooler, quieter, and less power consuming than before. Any questions or comments, feel free to post here.

note that i am using a 400MHz FSB CPU, 533MHz FSB CPUs will vary in mulitipliers and voltages.

 

[LumbergTech]

how much time did you gain on the battery life

 

[i game with a gateway]

well, if you leave it at the lowest multiplier, e.g. 6x, and it won't go higher than that, you can greatly increase battery life.

the default voltage for the 6x multiplier is:
0.988V and you're dropping it to 0.700V

the default voltage for the 16x multiplier is:
1.340V and I dropped mine to 1.020V

battery life for me (undervolted) is around 4 hours. this is with backlight on lowest, wifi on and browsing internet, and dynamic switching on. what i like about undervolting is that not as much heat is produced. like when i boot into linux, i cannot change my voltage as easily so i haven't, and the fan turns itself on very often and the temps are higher. for windows, with it undervolted, hell, my fan doesn't go on when browsing web or idling, it's not even on right now as i'm typing this. this should also prolong the life of the small little laptop fans inside as they don't have to work as hard or even turn on as much.

 

[Tseng]

To me the battery life is the 2nd consideration. The 1st is CPU temperture. Under-volting can keep the CPU run at a lower temperture even full speed.

The program I use is RightMark CPU Clock Utility. Same concept.

 

[Accord99]

There isn't much gain in typical situations, since Dothan at 800Mhz/0.988v uses so little power to begin with. At full load, it can be significant though that's not a common scenario for notebooks. For example, I have a P-M 730 that at 1.6GHz/0.952v, uses about 4-5w with cpuburn, full load, with a max temperature of 40C. That's less power than a typical 15.4" screen.

 

[vegetation]

Undervolting can really really help keep the fans to a minimum. I absolutely detest those little fans they put in laptop cpu's so the longer they are kept off, the better. With undervolting, I no longer need to have a cpu fan kick in during heavy internet browsing operation (even flash videos), so it's great.

 

[Carl Uman]

Thanks for sharing

 

[thecoolnessrune]

go for sticky. seems to be very few stickies in the Notebook area . Besides, this is nicely done and well written.

 

[Dadofamunky]

Great topic. I find it really cuts down on those unpleasant gusts of hot air out of the side of the lappie and doesn't hurt performance at all.

Everyone who owns a Centrino laptop should have this program.

I vote STICKY!

 

[computeerrgghh]

:thumbsup: Didn't know about this. I am going to try it out this weekend.

 

[Ionizer86]

Intel rates these CPUs way too conservatively. It seems that just about any Dothan can undervolt lower than an ULV Dothan at stock. No kidding about cutting down voltages by 25-30% or more.

 

[blingboi]

hey guys i just had a question, if i underclock using this method.. will it hurt the cpu if i like to alt-tab a lot while playing fullscreen games.

i'm pretty sure it would be switching back and forth to different clock settings

would it effect my cpu at all alt tabbing a lot?

 

[i game with a gateway]

thanks for the comments guys. I didn't think this thread would survive yet when I come back, it's still alive.

 

[blingboi]

Originally posted by: i game with a gateway
thanks for the comments guys. I didn't think this thread would survive yet when I come back, it's still alive.

could you answer my question? (does switching back and forth between cpu intensive(fullscreen game) to desktop cause any damage to my cpu.. its shuffling between clock speeds frequently)

just wondering if it would cause any damage

 

[i game with a gateway]

Originally posted by: blingboi
[could you answer my question? (does switching back and forth between cpu intensive(fullscreen game) to desktop cause any damage to my cpu.. its shuffling between clock speeds frequently)

just wondering if it would cause any damage

it shouldn't as even if you don't undervolt and you're using speed step, it will change the speed, obviously including voltage, when you alt-tab. it'll be say, at 1600MHz then you alt-tab and it'll be at 600MHz, even if you don't undervolt. it's built in by intel and i think they know what they're doing.

 

[Buck Naked]

I just tried this with a new toshiba M45, and found out that it is now using a Sonoma core.
The only difference is that sonoma has a FSb of 533 instead of 400.
It wants about 5 to 9% more juice.
6 multi @ .716
15 multi @ 1.116

But thx for the guide and links for the tools:thumbsup:

 

[i game with a gateway]

yah, i should have mentioned in the OP that it's the 400MHz version. i think i will edit it now just in case anyone gets confused with the multipliers and different voltages.