Undervolting: how low can you go?

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Re: thanks

Post by new2spcr » Sun May 03, 2009 10:40 am

Intel Core 2 duo 2.00 ghz

vcore @ stock - 1.32
undervolted via BIOS - 0.9x (can't remember the numbers right now)

Been running Orthos, blend stress test, RAM and CPU (thanks to wine!) for an hour and 20 min and temps don't go over 50 C for both cores:

sensors | grep Core
Core 0: +47.0°C (high = +74.0°C, crit = +100.0°C)
Core 1: +50.0°C (high = +74.0°C, crit = +100.0°C)

Ambient room temps: 25 degrees C.

Undervolting reduced the load heat by at least 8-9 degrees C!

Vcore undervolted at 0.8xx renders machine totally unbootable. Had to clear the RTC to gain access to the machine again.

...Orthos failed just now with this message:

Test 5, 5300 Lucas-Lehmer iterations of M13969343 using 768K FFT length.
FATAL ERROR: Rounding was 0.4739379883, expected less than 0.4

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Post by bhvm » Sun May 03, 2009 5:42 pm

Nice one there...
Is it a desktop or laptop?

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Post by new2spcr » Sun May 03, 2009 10:11 pm

bhvm wrote:Nice one there...
Is it a desktop or laptop?
It's a desktop.

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Post by bhvm » Sun May 03, 2009 10:55 pm

Intel has locked the minimum voltage to 0.95v for T2300

I bet my lappie could go far below that. Banias cores could go as low as 0.7v ( have 4 lappies with that)

yeah yeah... intel wants to sell LV and ultra LV processors hence the locks.

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Post by RedAE102 » Mon Jul 13, 2009 4:41 pm

Bought a new MacBook Pro 13" last week with the 2.26 GHz Core 2 Duo P7550. I'm using CoolBook to undervolt it, and quite an undervolter it is. Here are my results:

Core 2 Duo P7550 2.26 GHz
Stock Voltages:
0.875 V @ 800 MHz
1.000 V @ 1.6 GHz
1.0625 V @ 1.86 GHz
1.0625 V @ 2.0 GHz
1.125 V @ 2.13 GHz
1.125 V @ 2.26 GHz

0.875 V @ 800 MHz all the way to 2.13 GHz (minimum available VID even in Windows)
0.8875 V @ 2.26 GHz

If it was a 25W processor to begin with, it's now 15.6W processor.

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Post by nd4spdbh » Tue Jul 14, 2009 8:59 pm

my server that runs 24/7 i have undervolted.

E4300 c2d
2x1gb ddr2 667
Hitachi P7K500 500gb hd

Runs at its stock 1.8ghz but undervolted via a pad mod, idle @ 1.0125V load at 0.992 V ... loads round 45*C reported by coretemp cooled by an SI-120 with a custom socket 775 bolt through mounting. Best of all its quiet as hell... 3 fans... a 80mm adda low speed thats usually around 600rpms in the psu... and two 120mm antec tricools being fed 5v with their speed switch on medium!. The lil e4300 is a gem of a chip, it spent its life before server duty in my HTPC... it would do a 66% oc (3.0ghz 9x333) at 1.2500v (1.3250v stock!) i love it!

This is its case, with its old socket 478mobo n cpu... thats now been replaced with the above cpu and mobo... same hd setup, and SI-120.


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Post by BillyBuerger » Wed Jul 15, 2009 5:20 am

Ouch, that's a huge screen shot. Could you move all your windows to one side and crop that thing? I think there's a forum rule to keep your images less that 640 pixels wide.

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Post by nd4spdbh » Wed Jul 15, 2009 3:52 pm

better? lol... didnt think a 1680x1050 ss was gonna hurt n e one

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Post by yuu » Fri Jul 17, 2009 4:50 pm

Intel C2D E8400 E0 - PENRYN (775) stock - 1.250V

Minimum: 1.9 GHz @ 0.800V
OC'ed: 3.8 GHz @ 1.200V



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Post by k735123 » Thu Sep 10, 2009 5:00 am

CPU: AMD Semrpon 140 "Sargas" @ AMD Athlon II X2 440 "REGOR"
mobo: Asrock AOD790GX/128 (SB750)
PSU: Corsair 450VX

2700 MHz(13,5x200) @ 1,1000V stock: 1,3500V
2000 MHz(10x200) @ 0,9625V
1600 MHz(8x200) @ 0,8875V
by BIOS (ACC Auto)

800 MHz(4x200) @ 0,7375V
by OCTuner

Entered in BIOS Vcore <=0,7500V always shows as Vcore=1,2500V under 'BIOS HW monitor', 'CPU-Z' and other prog.
An old one:

CPU: AMD Geode NX 1750+ (stock: 10x133=1400MHz 1,25V)
mobo: Shuttle nForce2 Ultra
PSU: Corsair 450VX

1064 MHz(8*133) @ 1,100V
1600 MHz(8*200) @ 1,250V
1800 MHz(9*200) @ 1,425V
Last edited by k735123 on Mon Sep 14, 2009 12:43 pm, edited 4 times in total.

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Post by mlc » Sat Sep 12, 2009 12:37 am

Core i7 920 at 2.66 GHz w/ HT, SpeedStep & Turbo (2.8GHz) running at 0.9375V in BIOS, which shows under CPU-Z as 0.92V. CPU PLL at 1.8V, QPI at 1.2V and DRAM at 1.5V.

able to run 3.36 GHz at 1.1V cpu voltage in BIOS, 1.08V in CPU-Z.

Update: I've had a few BSOD's since, and so I've upped the voltage to 0.95V.
Last edited by mlc on Fri Sep 18, 2009 11:20 am, edited 2 times in total.

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Post by frostedflakes » Sat Sep 12, 2009 9:03 am

Athlon64 X2 3600+ (Brisbane, 65nm)

Stock: 1.9GHz, 1.35V
Undervolted: 1.9GHz, 1.025V

I'm kind of interested to hear more about how the 45nm AMD quad cores undervolt. Have been considering one of the new Athlon II X4s. :twisted:

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Post by mrle » Thu Sep 17, 2009 1:02 pm

I have an Athlon II X4 620:

Stock: 2.6 GHz @ 1.4V
Undervolted: 2.6 GHz @ 1.125V

Lowest P-state (stock): 800 MHz @ 1.15V
Undervolted: 800 MHz @ 0.925V

This is on AM2 board, though (NB runs on same power plane as the CPU). Maybe with an AM3 board one could lower the voltages by 0.025V more.

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Post by frostedflakes » Thu Sep 17, 2009 1:35 pm

Thanks for sharing mrle. I was considering the Athlon II X4 620, but went ahead and picked up a 550 BE because NewEgg had some pretty good mobo combos for that CPU. Hopefully I don't get unlucky and get one that can't unlock to quad core. Will be sure to post undervolting results once I get everything set up.

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Post by Manabu » Sun Sep 20, 2009 3:54 pm

My results are not as good as Lostfaith's 940 Black Edition, but for a cheaper cpu they look pretty good.

For all the results, I ran 2~8 hours of OCCT (or 8 hours of Prime 95) at 0.0125 ~ 0.0250 volts under the ones I marked there. So they are rock-stable, 24/7 every day undervolts/overclocks for this cpu. Aparently the minimum voltage that my motherboard supports is 0.8v (but I didn't tested it, I don't know why), so I didn't use anything lower. At this voltage I was runing even 1200mhz (but didn't ran prime in it).


The voltage curve is linear in all clocks, except above 3ghz. I didn't tried any higher OCs, as the step-up to 3.1Ghz already took that much more volts. The temperature was also in the 51°C, so I stopped. Probably I would have maxed out at 3.2~3.3Ghz. The motherboard was capable of more than 260mhz even with the onboard video enabled, but I would also rather not push it much.

The CPU/NB stock seems to be 2Ghz@1.275v, and I overclocked it to 2.3GHz @ 1.200V, and I'm runing it now 2.07Ghz @ 1.150v. Actualy, I was able to boot to windows and see HD videos @ 1.050v, but the OCCT would hang in less than 1 minute even with small data set even at 1.1v. Then ran some OCCT at 1.125v, 20min in each dataset size, and it passed. So I'm with 1.150v now (and I'm lazy to see if I can lower it one or two notchs). The HT also worked at up to 2.3Ghz, but I lowered it for some additional stability anyway.

My specs:
Processor: Phenon II X4 810 (stock: 2.6Ghz@1.3v in this motherboard at least) - serial number: "CACZCAC 0903 BPMW"
Motherboard: Asus M4A78T-E - AM3
Video Card: Onboard 790GX with sideport + 256mb UMA
Memory: 2x2GB OCZ3G1332G runing at 1226@7-7-7-1T 1.6v ("stock" is 1333@9-9-9 1.9v)
CPU cooler: Coolermaster Hyper TX2 with the pre-applied thermal paste - Set on silent profile on MB bios.
Case: Cooler Master Elite 335 - Fan set on silent profile on MB bios.
PSU: Corsair 400CX (80plus)

I also made an very rought estimate of my CPU and system power consumption at every undervolt setting. I don't have any wattage mesurement equipament, so I used this PSU calculator and tried to simulate my system encoding a video. I picked the Intel C2Q Q9300, as there was no 45nm PII avaiable, and the wattages seemed reasonable.

In the graphics below, the red bar is the CPU power consumption alone, and the blue bar is how much the entire system is sucking from the wall, with the PSU inefficiency curve already included. In the thumnailed graphic I simply took off the system power, for a better view of the cpu consumption alone.


The conclusion is that, even thought it is possible to reduce alot the CPU power consumption undervolting it, I'm not doing anything to the rest of the system. Thus, my encoding, for example, will drawn less power overal with the cpu runing at 2.6Ghz than 1Ghz, as it will finish sooner. (that is actually a lie, because I always try to encode at 0,7 fps, regardless of cpu speed, but anyway)

Also, I don't gain much going from 1Ghz to 800mhz if I mantain the same voltage. In fact, it seems like 1~2W difference. So I'm using 1Ghz in hope that the computer needs to jump p-stats less often that way.

I'm now runing with the following k10stat configuration:
2990mhz - 1.2625 v ("3ghz")
2300mhz - 1.1000 v
1610mhz - 0.9375 v
1035mhz - 0.8000 v

I had some problems of hiccups in HD video playback, letting windows adjust the clocks, or runing in the unganted mode, thus I set k10stat to start with -ClkCtrl:2 and it was aparently solved. No problems so far. The complete configuration:


Additional images of the system at load and after some time at idle (room temp was around 25ºC). Shows the k10stat old bus speed bug (from v1.35 ajustable by -HtRefClk) , CPU-Z, AMD overdrive main screen, prime 95 and Speedfan.


EDIT: Updated K10stat setings
Last edited by Manabu on Thu Apr 08, 2010 6:35 pm, edited 1 time in total.

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Post by Ksanderash » Sun Oct 04, 2009 1:22 pm

CPU: Pentium DualCore E6300(SLGU9, Wolfdale) 2.8GHz 1066MHz 2Mb
MB: Gigabyte GA-G41M-ES2L 1.0

Stock: 2.8GHz(266x10.5), 1.2875V
Stock undervolted: 2.8GHz(266x10.5), 1.0125V
Deep undervolted: 1.0GHz(166x6), 0.6720V :shock: (cold boot problem -- works in Windows, but boots only from 0.7V)

Validation: Image
(Prime95/Linpack stable)

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Post by hybrid2d4x4 » Sun Nov 29, 2009 4:32 pm

CPU: Pentium DualCore E5200 2.5GHz w/ semi-passive minja
Mobo: Gigabyte GA-E7AUM-DS2H (the GF9400 one)

CPU-Z shows 0.912V (had it at 0.896V for a week or so but eventually did get an application crash that may have been due to the low voltage, so it's now 1 step higher). 0.912V is a stable voltage for me as I've had it running at this voltage for several months before I decided to see how much lower I could go. Apparently, not lower at all...
Oh, and my temp sensors seem to be stuck at 36/39 for the 2 cores (except for the miraculous instance where it actually changed for one of the cores in the pic below). :?


Gaming Rig
CPU: Core 2 Quad Q9450 2.66GHz /w Ninja revB and fan @ 900RPM
Mobo: Asus P5Q Pro (P45)

CPU-Z shows 1.032V (1.050000V in BIOS). Load temps are 51-53 with occasional peaks at 55-56 on one of the cores at a time under Prime95 blend. Not too happy about the temps and I don't really want to bump up fan speeds, so I'm keeping it at stock speed until I decide to spring for a bolt-thru kit, then I might OC a bit (assuming it lowers temps a bit). At least it's >2.5hrs stable & error-free in P95!
Last edited by hybrid2d4x4 on Wed Dec 02, 2009 12:52 pm, edited 3 times in total.

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Post by Maverickâ„¢ » Tue Dec 01, 2009 3:18 am

hybrid2d4x4 wrote:HTPC
CPU: Pentium DualCore E5200 2.5GHz w/ semi-passive minja
Mobo: Gigabyte GA-E7AUM-DS2H (the GF9400 one)

CPU-Z shows 0.896V (sometimes alternates to 0.912V). Peak temps are 39 on both cores under Prime95 blend after ~45mins so far* and stable.

Hi, what are your default VIDs? the VID at full load (maxVID) and the VID in idle when EIST drop Vcore and multiplier (minVID)?
you can see those values with CoreTemp...


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Post by hybrid2d4x4 » Wed Dec 02, 2009 12:45 pm

With just a few mins under P95 load, my maxVID seems to be 1.2875V and minVID was 1.1000V, though I did see it momentarily switch to a different value (probably one step higher or lower). The voltage in CPU-z consistently showed 0.912V though (both idle and load) as I had it side-by-side with RealTemp, if that means anything...

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Phenom II 925 rev. C3

Post by Thomas » Mon Jan 18, 2010 1:15 pm

Phenom II 925 rev. C3

Idle: 0,74 volt / 800 MHz / 54-55 watts
Load: 1,18 volt / 2800 MHz / 125 watts

Measured @ 230volt AC without screen, speakers etc - undervolting with K10stat - voltages read through SpeedFan - system has been stabil for about 3 weeks.

Undervolting helped a lot on load wattage, it went from 180 watt to 125.

Other specs:

Gigabyte GA-MA78G-DS3H (integrated graphics)
2 x 2 GB RAM DDR2
Seasonic S12 380
1 x Samsung F2 EcoGreen
2 x Hitachi 5K160 2,5"
1 x optical disc 7240s
1 x card reader

With a 4850e in the same system, idle wattage was 42-43 watts, and around 80 watt @ load.

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Post by SleepyBum » Wed Jan 20, 2010 1:05 am

Athlon II X2 250

in a Shuttle SA76G2 barebone
AMD 760G + SB710

There is no FSB or voltage control in BIOS so all undervolting was done in K10stat

Stock: 3000Mhz 1.440V

Speed __ K10stat CPU-Z
3000Mhz 1.1500V 1.168V
2800Mhz 1.0875V 1.104V
2200Mhz 0.9500V 0.976V
1500Mhz 0.8125V 0.832V
0800Mhz 0.6750V 0.688V

Last edited by SleepyBum on Wed Sep 14, 2011 10:55 pm, edited 2 times in total.

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Post by George7 » Sun Jan 31, 2010 4:40 pm

The lowest I've gotten my i5 on stock speeds is 1.150v. Is this allright? I know it's not great but it seems a quite a bit for a 45nm chip. I can run 3.8ghz stable on 1.275 but for 4ghz I need about 1.4 which also seems a bit unusual.

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Post by WARDOZER9 » Mon Feb 01, 2010 4:09 pm

SG31G2 running an E7600 with 1.2875v vid.

Stock speed is untested

334.5 x 9 for 3010 mhz with 1.125v in RMClock ( 1.09v actual as far as programs read )

334.5 x 10 for 3345 mhz with 1.225v in RMClock ( programs read about 1.19v )

This is all the testing I've done on the CPU with undervolting atm.

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Post by mab » Mon Feb 08, 2010 11:49 pm

Aopen QF50J-400W / GA-MA78GM-S2H (rev 1.0) / Athlon X2 4050e / 2Gb Kingston ValueRAM KVR800D2N5K2/1G / WD5000AKS 500GB / GH20NS15.

Stock : 2100MHz @ 1.25V
Now : 2100MHz @ .95V Load

Aopen QF50C-350W / MSI K9A2GM Athlon X2 4850e / 2GB Kingston ValueRAM KVR800D2N5K2/1G / WD5000AKS 500GB / Mitsumi CR-480ATE.

Stock : 2500MHz @ 1.25V
Now : 2750MHz @ 1.25V Load / increased FSB only to 220

Tried to lower the CPU voltage with RMclock, CrystalCPUID and Overdrive. Only the last lowered the voltage but the CPU-fan ran faster so not OK. Still trying.

Both running BOINC 24/7

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Re: Undervolting: how low can you go?

Post by Heaven » Sat Jul 23, 2011 5:08 am

Hi all,
I tried and succeeded to undervolt a little my CPU, here are my settings and results:

My PC:
CPU: AMD Athlon 64 X2 5600+ Windsor @2800MHz
MB, GPU, RAM: http://valid.canardpc.com/show_oc.php?id=1920584

I`m using CrystalCPUID because with rmclock i got bluescreens even at stock voltages.

CrystalCPUID settings:

Undervolting results:

At minimum speed of 1004.6MHz if I select less than 0.825V (0.800V) firefox crash continuous and sistem is less stable.
At 2812.8MHz with less than 1.175V (1.150V) I get errors from Orthos in first 2-3 minutes of test.
I dont know why at 2800MHz even if the voltage in cristalcpuid is set for 1.175 CPU-Z shows me a value of 1.216V

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