Lower your load temps: minimize your vcore

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03-06-2007, 11:16 PM
graysky

Lower your load temps: minimize your vcore

Sounds pretty simple, but you'd be surprised how many people don't know about how much vcore can affect your load temps. Temp and frequency (FSB) have a linear relationship whereas temp and voltage have an exponential relationship. Conclusion: minimize voltage.

Here is the Intel document that helps explain it, see page 31:

Quote:

An increase in processor operating frequency not only increases system performance, but also increases the processor power dissipation. The relationship between frequency and power is generalized in the following equation: P = CV^2F (where P = power, C = capacitance, V = voltage, F = frequency). From this equation, it is evident that power increases linearly with frequency and with the square of voltage.

Same thing holds true for speed in a car: energy = 0.5mv^2 where m is mass and v is velocity. This is the basis of the old expression, "speed kills." You generate way more energy driving 75 MPH than you do driving 55 MPH since energy and velocity have an exponential relationship.

Anyway, to test how low you can go, simply manually set your vcore for something low. I started @ 1.2375 for my Q6600 running @ 9x333. If you can boot into windows load up a couple instances of orthos. If you have a quad make sure you set the CPU affinity such that one of the orthos gets cores 0 and 1 and the other gets cores 2 and 3. Let em run for a while. If the vcore is too low, one or both will give an error message. Orthos checks e when for rounding errors that can occur when the system isn't stable due to vcore, or temp, etc. Using a vcore of 1.2375v for my system gave an error pretty quickly:

http://img526.imageshack.us/img526/8...at12375vl1.gif

If you don't get an error after say, 30 min, lower the vcore in the BIOS and repeat until you do get an error, then start working your way up until you can run them with no errors for a good 6-8 hours. In a nutshell, that's it.

Enjoy.
04-06-2007, 01:07 AM
Phil_P

Thanks - that's really interesting. I didn't realise the exponetial relationship to vcore!

Quote:

Originally Posted by graysky

Anyway, to test how low you can go, simply manually set your vcore for something low. I started @ 1.2375 for my Q6600 running @ 9x333.

graysky - please tell us more...

at 9x333, what vcore did you use to achieve stability, and what were your load temps (and with what cooling). I believe the default vcore for the Q6600 is 1.2500v isn't it?
04-06-2007, 01:13 AM
Flewis

Just a note, the voltage increases quadratically (v squared) not exponentially.
04-06-2007, 01:48 AM
graysky

Quote:

Originally Posted by Phil_P

graysky - please tell us more...

at 9x333, what vcore did you use to achieve stability, and what were your load temps (and with what cooling). I believe the default vcore for the Q6600 is 1.2500v isn't it?

Without doing the pencil mod for vdroop on my P5B-Del, I was stable with a BIOS value of 3.1250v which after the droop (as per readings in CPU-Z), was 1.232v.

After I did that pencil mod, I now have the BIOS set to 1.2625v and I have no vdroop at all (load to idle). CPU-Z reports an idle vcore of 1.232v (about 31 mV off from the BIOS). It is stable to 2x orthos for >6 h.

@Flewis - I guess you're right about that relationship. It's been a while since I had calc.
04-06-2007, 02:56 AM
Phil_P

Can you tell us what cooling you're using and what your load temps are please?
04-06-2007, 09:37 AM
graysky

Lapped Q6600
Lapped Ultra-120 Extreme

First speak to the cooling.

Room temp as it affects load temps - you can see a table in here with my average load temps over 6 or 7 different room temps.
04-06-2007, 11:37 AM
DougMcDonald

Quote:

Just a note, the voltage increases quadratically (v squared) not exponentially.

Erm, quadratic equations do have an exponential rate of increase, 2 is the exponent, v squared, v to the power of 2 - your talking about the same thing :P

There is no such thing as a quadratic increase as far as i'm aware.
04-06-2007, 11:49 AM
Flewis

i meant v is not the exponent to clarify
04-06-2007, 01:08 PM
hibby

Quote:

Originally Posted by DougMcDonald

Erm, quadratic equations do have an exponential rate of increase, 2 is the exponent, v squared, v to the power of 2 - your talking about the same thing :P

There is no such thing as a quadratic increase as far as i'm aware.

Actually no, an exponential function would be 2^v whereas a quadratic function is v^2. :p
04-06-2007, 01:09 PM
Flewis

Thats what i meant initially.
04-06-2007, 02:18 PM
DougMcDonald

Quote:

Actually no, an exponential function would be 2^v whereas a quadratic function is v^2.

This is right, but for the purpose of the topic, when talking about exponential increase, you would be referring to a constant to the power of an exponent; so the v^2 you describe.

In this context, exponential would purely be used to differentiate between the linear rate of increase such as 2x compared to the exponential increase of x^2
04-06-2007, 02:29 PM
Phil_P

Quote:

Originally Posted by graysky

Lapped Q6600
Lapped Ultra-120 Extreme

First speak to the cooling.

Room temp as it affects load temps - you can see a table in here with my average load temps over 6 or 7 different room temps.

Thanks :)
14-06-2007, 01:11 AM
graysky

Here are the results from a little experiment I just finished wherein I ran p95v2 with 4 threads doing large FFTs for ~1 h on a Q6600 @ 9x266 under two different vcores: 1.2625V in BIOS or 1.232V in CPU-Z and 1.1125V in BIOS or 1.080V in CPU-Z. I had the logging disabled so these aren't average temps, just "instant" temps although I they really did level out.

Results @ 1.232V:

Code:

Core0=55 Core1=56 Core2=51 Core3=52

Results @ 1.080V:

Code:

Core0=49 (6 °C cooler) Core1=50 (6 °C cooler) Core2=48 (3 °C cooler) Core3=48 (4 °C cooler)

Result: 152mV in vcore can make a pretty big difference in temps. Oh, room temp for this was 75-76 °F throughout.
14-06-2007, 01:28 AM
arthurleung

Core2Duo T7200 Merom

Stock: 1.187V
Full Load -> 87'C
Idle -> 63'C
Tdiff = 24'C

Undervolted: 0.975V
Full Load -> 74'C
Idle -> 59'C
Tdiff = 15'C
23-06-2007, 11:29 AM
graysky

Here is a more detailed analysis of two difference vcore settings and the temps they produce on a Q6600 @ 9x266=2.4 GHz as well as @ 9x333=3.0 GHz. The two voltages I used were 1.112 V and 1.232 V (both of these are the load voltage, the actual BIOS settings were 1.1375V and 1.2625V respectively).

2x orthos ran for 30 minutes and the temperatures were averaged over the last 10 minutes of those runs (well after they stabilized). Room temps was 75-76 °F. Notice that the difference in voltage is ONLY 0.120 V or 120 mV, but this seemingly small difference brought the load temps up by an average of 6-7 °C per core!

Code:

Run1 (9x266 @ 1.112 V), Average temps (°C): 51,52,50,50 Run2 (9x266 @ 1.232 V), Average temps (°C): 57,58,57,57 Differences (°C): +6, +6, +7, +7

Now if I add a faster FSB, they increased further:

Code:

Run3 (9x333 @ 1.232 V), Average temps (°C): 61,61,60,60 Differences from lowest voltage (°C): +10, +9, +10, +10 Differences from same voltage (°C): +4, +3, +3, +3
23-06-2007, 11:54 AM
Robbie G

Quote:

Originally Posted by Phil_P

Thanks - that's really interesting
graysky - please tell us more...

Lol, you sound like Jimmy from South Park in the episode where he's trying to get laid with that hooker, Nutgobbler.