core2duo undervolting tips?

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Conroy
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core2duo undervolting tips?

Post by Conroy » Mon Jan 21, 2008 9:38 am

I have been undervolting my dothan laptop using RMClock for several years, and it's been working great.

Since that has been working so well, I am now investigating undervolting my core2duo desktop as well. I read through threads here, and it looks like the process might be more complex. Searching through the net finds lots of guides for undervolting notebooks, but not so much on desktops.

When I use RMClock with my notebook, it displays the voltage at minimal speed (6x), and the voltage at maximal speed (15x). I can then find and set optimal voltages by simply adjusting these 2 voltages and testing at both speeds.

My GA-P35-DS3P bios, however, has different types of settings.. mainly, it just has a single voltage setting for the CPU. Should I be using that, or can RMClock support something similar to what I was doing on the notebook?

Actually, my GA-P35-ds3p also has a bunch of settings i don't completely understand - something called "CPU Intelligent Accelerator" which automatically overclocks, and a "Performance Enhance" with "turbo", "standard", and "extreme" settings. I guess this is for another thread though; I'm probably going to leave this stuff disabled because I don't want to risk the board interfering with voltages, although xbitlabs says that the settings are important for the system performance.

aaa
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Post by aaa » Mon Jan 21, 2008 1:15 pm

RMClock should work, just like you'd do with a laptop.

I'd leave the BIOS settings alone. Overclock only if you need to, and I would prefer manually overclocking over the automatic settings.

jessekopelman
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Post by jessekopelman » Mon Jan 21, 2008 1:20 pm

If you are going to use RMClock to do your undervolting, you can pretty much ignore all your BIOS settings except for EIST -- you want to enable EIST. All of the ones you listed are for overclocking and many of them will try and increase various voltages to increase stability and will be counter to your purposes. To fully enable EIST you also have to enable it in your OS (in XP, this involves setting a Power Scheme in the Power Options control panel). Turning on EIST will make it behave like your Dothan. It will have two default voltages: one at 6X and one at whatever the top multiplier is. The default voltage at 6X is 1.13V and the voltage at full speed is 1.32V. You should be able to easily get the full speed voltage down close to 1.1V, but getting the lower voltage much lower than 1.1V seems to be hit or miss.

leifeinar
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Post by leifeinar » Mon Jan 21, 2008 2:32 pm

wich cpu are u using? its very easy to undervolt the gigabyte card. install easytune and prime95 then u can lower voltage while running the stability test. i used 10 min to roughly find lowest vcore. got a quad running at 0,96V. when u find stable voltage u just go innto bios and sett the same value

Conroy
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Post by Conroy » Mon Jan 21, 2008 7:59 pm

Thanks! So I'll leave all the performance enhancers disabled or set to "standard" to make sure it's not doing anything funny and start with RMClock (and prime95).

I'm using an e8400, and I'll post my results this weekend.
I'm planning to try to figure out the lowest voltage I can use at the stock clocks, the highest fsb I can get at the stock voltage, and hopefully a couple of steps in between.

I had assumed I could go into BIOS and set the voltages after finding the values with RMClock, but the bios only has a single cpu voltage value while RMClock uses at least 2 values, so I'm not sure how that translates? It sounds like I would be better off just using RMClocK.

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Post by smilingcrow » Tue Jan 22, 2008 12:54 am

Conroy wrote:I had assumed I could go into BIOS and set the voltages after finding the values with RMClock, but the bios only has a single cpu voltage value while RMClock uses at least 2 values, so I'm not sure how that translates? It sounds like I would be better off just using RMClocK.
RMClock is limited to using the natural voltage range of a CPU which is roughly 1.15 – 1.325V for a 65nm Core 2 Duo. If you require less or more than this for under-volting or over-clocking you need to use the BIOS setting which will limit you to a single fixed value.
At stock speed many C2Ds are stable at substantially lower voltages than 1.15V so you are better off with manually lowering the voltage in the BIOS.
For extreme over-clocking you’ll need more voltage than RMClock can provide so again you’re better off with manually setting a voltage.
There is a sweet spot as far as I’m concerned which allows you to over-clock using the natural voltage range which still allows the voltage to drop at idle; the best of both worlds you could say. You need to test to find the highest FSB that is stable using the maximum voltage that RMClock provides and then deduce what voltage you require at the idle clock speed.
leifeinar wrote:wich cpu are u using? its very easy to undervolt the gigabyte card. install easytune and prime95 then u can lower voltage while running the stability test. i used 10 min to roughly find lowest vcore. got a quad running at 0,96V. when u find stable voltage u just go innto bios and sett the same value
Thanks for the info as I hadn’t realised that easytune allowed such low voltages; as you say that’s very useful. I’ve been so unimpressed with motherboard manufacturer’s over-clocking utilities over the years that I’ve stopped looking at them.

Mikael
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Post by Mikael » Tue Jan 22, 2008 3:04 am

There is probably little reason to have EIST activated on an undervolted E8400, since the power savings would likely be very small. I'd just fix the CPU frequency to the stock 3GHz and try to get the voltage down to ~1.0V (which is definitely a possible target) using the BIOS setting.

Conroy
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Post by Conroy » Tue Jan 22, 2008 12:36 pm

Great, I'll check out easytune as well and see what that can do.

I think my main confusion has been that the bios sets a single voltage level, when the voltage should actually vary depending on what EIST is doing. Is the bios setting the voltage for max speed and then extrapolating down from there for lower multipliers somehow?

I hadn't thought about disabling EIST.. I just assumed that letting the cpu clock down when it didn't need the speed would always be a good thing. What are possible disadvantages to EIST?

I guess that's one more thing to try out.

aaa
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Post by aaa » Tue Jan 22, 2008 2:57 pm

I don't think the BIOS extrapolates anything, it just disables EIST whenever you change the voltage.

EIST on the Core cpus has an arbitrary lower voltage limit (unlike your Dothan, which let you go down to 0.7v). I believe someone mentioned earlier that this limit is 1.15v. So the reason you'd go with the one-voltage-for-all BIOS would be that it might be possible for full speed to operate at a lower voltage than 1.15v, which you would only be able to use via the BIOS. If the voltage is significantly lower then it might make up for the increased power usage from higher speed.

Conroy
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Post by Conroy » Tue Jan 22, 2008 3:33 pm

Okay, that makes sense.
Thanks!

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