Lower your load temps: minimize your vcore

[graysky]

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:

 

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:

 

 

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.

[hardnrg]

that's all fine and dandy, but what if you the processor's overclocking results continue to scale with voltage, and temperatures are the limiting factor?

[GuJuMaN89]

lets say we are running at stock clocks, is it safe to reduce the vcore? (running fx55)

[jammin]

Well, it doesn't really hurt to reduce the voltage a bit.

 

You can undervolt a chip provided it's still stable, and it will run cooler.

[hardnrg]

you could do what I did with my Opteron 146's and 148... record the max overclock at vcore from 1.0 to 1.7v, plot a graph in Excel, decide what vcore (and therefore speed) you want if you're going for temperature targets

 

it takes a while...

[graysky]

that's all fine and dandy, but what if you the processor's overclocking results continue to scale with voltage, and temperatures are the limiting factor?

 

The overclock should scale with voltage, or I think really the overclock is a function of the vcore. It [overclock (given FSB x given multiplier)] can be limited by the temps produced, but long as that overclock is stable to an others test for a good amount of time @ the vcore you're running, you will be minimizing those temps by running at the lowest vcore that's stable. Does that make sense?

[graysky]

lets say we are running at stock clocks, is it safe to reduce the vcore? (running fx55)

 

Jammin hit the nail on the head: as long as the vcore you've selected falls within the manufacturer's range. For example, Intel gives a range of 1.100V-1.372V for my processor. I dunno about the FX55, but I'm sure you can find out from AMD.com

Edited June 11, 2007 by graysky

[Bleeble]

I think this is the first time I've ever seen hard data before, but... I thought most people knew this already. I guess not.

[graysky]

Here are the results from 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:

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

 

Results @ 1.080V:

Core0=49 (6 

[hardnrg]

The overclock should scale with voltage, or I think really the overclock is a function of the vcore. It [overclock (given FSB x given multiplier)] can be limited by the temps produced, but long as that overclock is stable to an others test for a good amount of time @ the vcore you're running, you will be minimizing those temps by running at the lowest vcore that's stable. Does that make sense?

oh I see what you're getting at... avoiding using unnecessary vcore... I just run all my processors as fast as they can go... if they used one notch lower vcore they would fail... but none of them are using low vcore lol... but it *is* the lowest possible, all the same

[Guest ecthlipsis]

My cousin has the Xeon version of the E6700 and he has it slightly OC'ed to 3.1ghz. He lowered his vcore until it became unstable and then raised it back just a bit more to be safe. The end result? He's running an OC'ed processor at LESS than stock voltage 100% stable =)

 

I believe this is the type of vcore reduction graysky was speaking of.

 

I'm with Hardnrg, though, in that if I lower my voltage my cpu becomes unstable. This is the minimum voltage I can run this OC at, lol.

[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