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Lower your load temps: minimize your vcore

Last response: in Overclocking
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June 3, 2007 10:16:54 PM

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:



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.
June 3, 2007 10:47:37 PM

Good post, but isn't that a quadratic relationship? I guess "exponential" gets the point across better, since it's colloquially used more often, but strictly speaking wouldn't that mean the voltage is the exponent?
June 3, 2007 11:04:58 PM

For my AMD64 X2 3800+, lowering the voltage has almost no effects on my core temps, they idle mid-40s no matter what. Tried it for a while, but it really didn't seem to do anything. I was risking stability for no temp drop. Maybe it would have made more of a difference if I wasn't on stock cooling, but I dunno.
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a b à CPUs
June 3, 2007 11:45:48 PM

old news
June 3, 2007 11:50:47 PM

Quote:
old news


Maybe old to you, but I'm sure someone will find it helpful :p 
June 4, 2007 10:04:10 AM

Maybe old but definately worth restating when people are running around with 1.5+ vcores on e6xxx and e4xxx CPUs harping about temp issues
June 4, 2007 10:41:49 AM

But I can't lower my voltage T_T I'm running an Opteron 165 @ 2,5Ghz and these damn things run 1,4 volt stock at that frequency. -_-


Would watercooling reduce the need for a higher voltage?
(wich I will be receiving any day now anyway)
June 4, 2007 8:55:29 PM

Quote:
But I can't lower my voltage T_T I'm running an Opteron 165 @ 2,5Ghz and these damn things run 1,4 volt stock at that frequency. -_-


Would watercooling reduce the need for a higher voltage?
(wich I will be receiving any day now anyway)


No, a more efficient heat exchange won't change the intrinsic property of your chip: there is a need for a certain voltage to run at a given clockrate period.
a b à CPUs
June 5, 2007 12:31:07 PM

Quote:
old news


Maybe old to you, but I'm sure someone will find it helpful :p 

true that

you do know the true required vcore for all cpus is alot lower then what there officially rated right? but because of the wide range of motherboards and psus and configurations the vdroop, the vcore is put up so all boards will work fine etc, so thats why you can overclock without an increase in vcore, and why you can lower the vcore and not compromise stability (and hence why cheaper boards wont go as far with stock vcore etc) ;) 
June 6, 2007 9:31:37 AM

Actually that is what got me into undervolting my OC. Notice the actual Vcore of the e4300 starts at 1.225 and ranges up to 1.325.
http://processorfinder.intel.com/details.aspx?sspec=sl9...
My chip will run 334 x 9 orthos stable with an actual Vcore of 1.264 per cpuz. Granted it took 1.36 actual volts to initially hit 3.2ghz orthos stable, it now handles it on 1.346. 8)
June 6, 2007 12:12:57 PM

You may be "living" on the top of a flux, though, if you're very close to the limit you may crash when firing up the graphics card or so.

Just a thought.
June 6, 2007 12:46:03 PM

I lowered my vcore and fsb voltages but it didnt affect temps at all which is not incorrect just means need to fallback on lowering FSB :) 
June 6, 2007 1:22:32 PM

Good valuable post for the uniformedd graysky. Voltages make a big difference. In a 20C room, my chip will idle undervolted at stock speeds at 18-21C. With stock voltage, the idle bumps up to 21-23C.

@ asdasd123123: if you have a decent mobo, you should be able to hit 2.5 with less than 1.4V. My 170 is just an average chip and it will run stock at 1.2V and all the way up to 2.7 on 1.3V, the stock voltage.
June 14, 2007 12:10:10 AM

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:1:5dc3cba6b0]Core0=55
Core1=56
Core2=51
Core3=52[/code:1:5dc3cba6b0]

Results @ 1.080V:
[code:1:5dc3cba6b0]Core0=49 (6 °C cooler)
Core1=50 (6 °C cooler)
Core2=48 (3 °C cooler)
Core3=48 (4 °C cooler)[/code:1:5dc3cba6b0]

Result: 152mV in vcore can make a pretty big difference in temps. Oh, room temp for this was 75-76 °F throughout.
June 14, 2007 1:03:07 AM

Any advantage doing this over enabling CnQ or eist?
June 14, 2007 2:02:31 AM

Yeah, but only at idle... when stressed, speedstep won't kick in.
June 23, 2007 10:26:54 AM

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:1:f8f6cf9a4b]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[/code:1:f8f6cf9a4b]

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

[code:1:f8f6cf9a4b]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[/code:1:f8f6cf9a4b]
June 23, 2007 11:12:59 AM

The conclusion of this, is what was already told, so many times, with graysky making it objective:
- vcore is the first source of heat
- CPU speed is another important source of heat

For my personal point of view, there are more important causes of heat. But in this case it is about heat dissipation and not production:
- HSF (up to 20-25°C difference on air, and even more on WC/TEC)
- Thermal compound application and the interface (lapping, removing IHS): up to 10-15° if considered together
- Case ventilation: up to 15-20° for the worst cases

I'd say, get your most stable overclock speed, and lower the vcore until lowest stable. On SLI configuration, I'd say: lowest stable vcore + one notch depending on your PSU +12v rail stability
!