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:

Orthos error pic

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.

 

[myocardia]

Good thing for the noobs to be finding out about.

 

[manimal]

Seconded. It took me years to figure this out. I would buy great parts and just install and start gaming, never testing, never tweaking, just playing. As I play less and less I play with my hardware more and more lol.

 

[Idontcare]

Changing to manual voltage in the BIOS comes at the expense of disabling the voltage reduction power savings mechanisms that Intel/AMD built into the chips for idle times.

You don't get the best of both worlds, reduce Vmax at full load but continue to run at that same Vmax when idle...or allow Vmax to run at stock when loaded and have EIST/Cool-n-Quiet drop your voltages when the chip is idle.

 

[frostedflakes]

You can use programs such as RMClock to modify FID/VID settings in Windows for CnQ and EIST.

 

[betasub]

Same applies to GPUs: if you sacrifice your core overclock, you can run your GPU with lower voltage and seriously lower heat. Particularly handy for x1800/x1900 cards where the stock cooler spins up and gets noisy if GPU temperature rises too high.

 

[graysky]

@frostedflakes: i think that's dependent on your chipset. RMClock cannot manage my P5B Del. at all.

 

[lopri]

OP: Thanks for the quote. It's something of the obvious but I wasn't aware of the formula. Until now I thought clock frequencies had a bigger effect on power/temp than voltages.

 

[graysky]

Glad to share. I can't really take credit for that... someone else posted it somewhere and I bookmarked it. Wish I could remember who and where.

 

[aka1nas]

Depending on your board and how far you OC your CPU, you can sometimes use features like C&Q while overclocking. If your board has an "overvolt by %" type option you can use that in lieu of changing from the stock vCore. Typically, this will work with C&Q at least, but your maximum stable OC will be reduced somewhat. I.E. with the rig in my sig, I can run the chip at 2.6Ghz with C&Q or 2.8 without.

 

[graysky]

Here are the results from a little experiment I just finished wherein I ran http://mersenne.org/gimps/p95v2414.exe[/l] 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 °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.

 

[Johnny Nuge]

I've got my E4300 at 1.3875v in BIOS, fluctuating at either 1.344v or 1.328v idle and 1.312v under load in CPU-Z. Can anyone tell me what my CPU's vCore really is?

And yes, dropping vCore DOES significantly lower temps under load.

 

[dandragonrage]

I don't feel like reading the link but I will add a little information that I thought of. When I first saw that equation, I was wondering where it came from, so here's what I came up with:

CV^2 is an equation for energy - not power - stored in a capacitor. Energy is measured in joules which is the same as watt-hours (Wh) and conversely watts are joules/second. So then CV^2 is joules and we need joules/second, we take the period of the waveform, which happens to be the inverse of the frequency or 1/f, and divide by that to get CV^2/(1/f) or CV^2f.

And we're using this on the internal capacitance of the CPU for energy storage? Interesting.

 

[Nathelion]

Well P = I^2*R where P is power (which in this case equals heat), I is current, and R is resistance. Now I=V/R where V is voltage, and since a cpu is a constant resistor (I imagine that the resistance would be a function of the clock frequency, but it is can be considered constant for our purposes here since it's not a function of voltage) we get in effect
P = V^2/R, which means that power is proportional to the square of the voltage. I highly doubt that it has anything to do with capacitance.

 

[SerpentRoyal]

Originally posted by: Idontcare
Changing to manual voltage in the BIOS comes at the expense of disabling the voltage reduction power savings mechanisms that Intel/AMD built into the chips for idle times.

You don't get the best of both worlds, reduce Vmax at full load but continue to run at that same Vmax when idle...or allow Vmax to run at stock when loaded and have EIST/Cool-n-Quiet drop your voltages when the chip is idle.

Setting Vcore to AUTO/DEFAULT will work with the P5B Deluxe and 1101 BIOS up to 280MHz FSB. Above that speed, you'll still see the drop in Vcore and multiplier in Speedfan, but the actual current draw from the AC outlet DOES NOT DECREASE (speedstep is disabled).

See my post:
http://forums.anandtech.com/me...AR_FORUMVIEWTMP=Linear

 

[dandragonrage]

I was talking about the formula in the OP, because I didn't really get why it was being used. Well, I still don't, but I see where it came from, anyway.

 

[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!

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:

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

 

[ForumMaster]

kind of a problem for me. i have an ASUS A7N8X-X motherboard and an AMD Athlon XP-M 2400+ Oc'ed to 2.2Ghz. not this chip is rated for 1800Mhz at 1.45v. however, the lowest voltage my mobo supports is 1.575 and yet it runs the chip at 1.62. my CPU at load never get's above 45C and idles at 35C. i suppose i could try a higher Overclock but it's enough for me.