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 Post subject: My experience on undervolting & overclocking Core 2 Duo
PostPosted: Sun Aug 13, 2006 5:54 pm 
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I have been evaluating an Asus P5W DH Deluxe with an E6300 and E6400 for the last 4 or 5 days. The system as tested consisted of the following:

Intel E6400 2.13 GHz
Samsung P120 250GB SATAII
NEC DVD Burner & floppy drive
Corsair XMS2 DDR2 PC2-5400 2 x 1GB
Gigabyte GF6200TC 128 MB RAM (256MB with System memory)
PCI WiFi card (B/G)
Scythe Ninja + with Nexus 120mm
Arctic Silver 5 thermal paste
Antec P180 with Silverstone ST30NF (Fanless)
2 Nexus 120mm fans – one in lower chamber, the other as exhaust on the side of the case opposite the CPU
Windows XP Pro SP2

All three of the fans were set to 45% using Speedfan which reported the speeds at ~ 620 RPM. The hard drive was resting on acoustic isolation foam and located in the bottom chamber of the case; AAM was set to the quietest mode.

The stock VCore for both CPUs is 1.325V at full speed and 1.15V when Speedstep drops the speed to 1.6 GHz.
The BIOS doesn’t allow the VCore to be set lower than 1.225V. I was able to under-volt using CrystalCPUID, but no lower than 1.16V.
You can’t set a voltage manually in the BIOS and still use Speedstep.

I measured the power consumption at three states: idle, running two instances of CPU Burn-in and running two instances of Prime95 (In-place large FFTs (Max heat & power consumption)). The information below is in the format:

GHz, VCore, Watts (Idle, CPU Burn-In x2, Prime95 x2), Ambient Temp, CPU Temp, FSB (if not stock), No of Hours Tested Stable with dual Prime95.
xx is used where no reading was taken.

1.60 GHz / 1.150V / 088 097 105 Watts / 25 xx
2.00 GHz / 1.150V / 088 100 111 Watts / 25 37 / 250 / 2
2.13 GHz / 1.150V / 088 102 112 Watts / xx xx / FAIL

2.13 GHz / 1.325V / 100 115 126 Watts / 25 xx
2.80 GHz / 1.325V / 103 124 135 Watts / 26 48 / 350 / 12
2.90 GHz / 1.325V / 103 124 136 Watts / 22 46 / 362 / 2
3.00 GHz / 1.325V / FAIL
3.00 GHz / 1.400V / 111 137 149 Watts / 26 55 / 375 / 1
3.20 GHz / 1.450V / 119 150 163 Watts / 26 60 / 400 / 1

In the last two tests I had to raise the CPU fan speed in an attempt to keep the CPU temperature below 55C. Even at 100% it couldn’t keep the temperature from rising uncomfortably.
I suspect that the thermal paste may not have been optimally applied due to the fact that I swapped out the CPU whilst the motherboard was still in situ. I found it very difficult to install the Ninja in this scenario and the paste may have been spread slightly away from the optimal contact zone. If I was keeping the motherboard I would certainly have removed it from the case to install the Ninja.

I didn’t have the time to test every permutation of CPU speed and VCore fully, so it may be possible to squeeze a bit more efficiency from this particular CPU.
I did some testing with an E6300 initially and when running that at 2.80 GHz with stock VCore the system consumed 5W more than the E6400 when running dual Prime95. This is due to the FSB needing to be run at 400 versus 350 for the E6400. The E6300 has a multiplier of 7 versus 8 for the E6400.

One thing to consider when over-clocking a C2D is that motherboards using the P965 chipset don’t currently allow the RAM to run slower than the FSB. The Asus board that I used supports running the RAM/FSB with a ratio of 3:4. (It also supports running them synchronously and with the RAM faster than the FSB).
The advantage of this is that you can run an E6300 at 2.8 GHz using inexpensive PC2-5300 RAM. In fact, even at 3.2 GHz you can still use PC2-5300 as it will only be very slightly over-clocked.
In a P965 based board you’d need to use PC2-6400 (800), as 2.8 GHz with an E6300 equates to a FSB of 400.
PC2-5300 typically uses 1.8V, whereas PC2-6400 is typically 2.1V, so you pay a double price for the higher speed RAM, in $ and Watts.

The downside to the 975X chipset is that it’s built on an older process than the P965, so should consume more power. Hopefully, one of the forthcoming non Intel chipsets will also allow a RAM/FSB ratio of 3:4 and be manufactured at 90nm. That would seem like the best option. Although, it’s possible that the P965 based boards may get BIOS updates that allow the RAM to run slower than the FSB, unless this is a limitation of the chipset!

To use Speedstep and over-clock with this setup you have to use the stock voltages, which limits you to the range 2.0 to 2.9 GHz; 2 GHz being the highest stable speed at 1.15V and 2.9 GHz being the highest stable speed at 1.325V.
For the E6400 used this implies a FSB of 1333, which gives a Speedstep range of 2.0 – 2.67 GHz and an optimal RAM speed of 667.
For an E6600 (2.4 GHz, multiplier = 9) at the same FSB you will have a Speedstep range of 2.0 – 3.0 GHz. It’ll be hit and miss whether it will be stable at that speed on stock Vcore, so you may need to back off the FSB to make it stable. I’m not sure if the extra cache of the E6600 and higher will make a difference to over-clocking stability!

It might also be possible to over-clock more aggressively using CrystalCPUID. By this, I mean that you use custom Speedstep voltages set with CrystalCPUID and then over-clock the FSB to a higher level than is stable using stock Speedstep voltages. You obviously choose a higher FSB value that is stable with the CrystalCPUID voltages that you set.
The danger in doing this is that the system will be running at an unstable setting for the 30 – 60 seconds or so it takes for Windows to load and CrystalCPUID to take over the voltage settings. If the settings chosen aren’t that aggressive and are unstable at the lower Speedstep frequency rather then the higher one, then I don’t think it will be such an issue. I suggest that stability at the higher Speedstep frequency with stock Vcore is more important, as whilst Windows is loading the system is more likely to be running at the maximum clock speed as it is under load.
In fact, even though the E6400 that I tested failed at 2.13 GHz at 1.15V, this test was conducted with both cores running at 100%. In everyday usage, if this system was over-clocked, it would never run at 2.13 GHz at 100% load, since Speedstep would bump it up to the max clock speed before that happened. This makes it more likely that the system would be stable in the period before CrystalCPUID took charge of voltages.

As an example for the E6400:
It was stable at stock Vcore at 2.9 GHz (FSB = 362).
This gives a lower Speedstep clock speed of 362 * 6 = 2.17 GHz.
It was not Prime95 stable at 2.13 GHz with stock Vcore, but was at 2.0 GHz
Well, there’s only one way to find out :)

Conclusions:

Cooling a C2D silently with this setup is easy provided you keep the VCore at stock.
Using Speedstep will reduce your idle power consumption by up to 15W using stock VCore values.
If you disable Speedstep and over-clock by increasing the VCore, your idle power consumption will climb very quickly for little performance gain.
E.g. 2.9 GHz with Speedstep = 2.17 GHz @ 1.15V = 88W
3.2 GHz @ 1.45V = 119W.
That’s a 31W increase at idle for a < 10% clock speed increases. The wattage difference at full load is slightly less at 27W.
Note. The difference would be slightly less, as in this scenario you would need to increase the Vcore with CrystalCPUID to gain stability. (See above).
If you are using Speedstep then you don’t need a motherboard that supports memory dividers, as a FSB of 1333 is about as far as you can push it at stock VCore values. This is synchronous with PC2-5300.
Higher FSB and RAM speeds consume more power for the same CPU clock speed, for typically little performance gains.
If you want to go for a large over-clock with an E6300 and a P965 chipset motherboard, you will need very fast and expensive RAM. It would probably end up costing you more than using a 975X based motherboard with slower RAM and very likely consume more power.
A power consumption comparison of the different chipsets for C2D would be useful. ASRock have a very cheap VIA based C2D board that might well consume little power. But, I assume it doesn’t support Speedstep, so it will be at a 12 – 15 W disadvantage at idle.

The system at almost all times during testing was quiet to the point of being ‘almost’ totally inaudible, even after midnight when the ambient noise floor is very low. The only time the noise level rose was when I increased the CPU fan speed due to over-volting the CPU in the last two tests.

Notes.
The power consumption of Prime95 at its most aggressive settings is I suggest atypical for most systems. The dual CPU Burn-in power values may well be more typical. This will lead to lower CPU temps than reported also.

The Asus P5W DH Deluxe uses the Intel 975X chipset and is fully featured; Crossfire support, eSATA, WiFi, Firewire, 2 Gigabit NICs, 2 PATA connectors. It uses heatpipes for cooling and comes with a fan that can be optionally used to improve cooling. It has 5 fan headers (one 4 Pin), at least 3 of which adjustable with Speedfan; there’s a fourth Speed control in Speedfan but I didn’t test to see whether it controlled the 2 fan headers that weren’t utilised.


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PostPosted: Sun Aug 13, 2006 7:02 pm 
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So the conroe is only 15W cooler at 1.15V than at stock voltage. That is probably not enough for me to run it totally passive. I'm gonna have to keep waiting for a better undervoltable motherboard.

Thanks for posting all that. It is a major help to all of us.


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PostPosted: Sun Aug 13, 2006 7:28 pm 
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autoboy wrote:
So the conroe is only 15W cooler at 1.15V than at stock voltage.
1.15V is stock voltage for the lower Speedstep frequency. When I say that Speedstep saves you up to 15W, this is comparing 1.6 GHz at 1.15V versus 2.9 GHz at 1.325V – 88W v 103W. I choose 2.9 GHz for the comparison as it’s the highest stable speed that I could achieve with Speedstep enabled.

It may well be that 1.15V is the limit for C2D in the way that 1.1V is for AMD. Unless you reduce the idle Speedstep frequency of 1.6 GHz by lowering the FSB, there isn’t going to be much headroom to reduce the voltage anyway. Since 2 GHz was the maximum stable speed at 1.15V, I can’t see that you will be able to under-volt that much at 1.6 GHz.

My Core Duo laptop also seems to have hard wired limits when using CrystalCPUID. I can’t set it to lower than 1.004V or higher than 1.404V. The later is the stock voltage for the maximum clock speed and means that it is not possible to over-volt in software, which is also true for C2D, I forgot to mention this.


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PostPosted: Sun Aug 13, 2006 7:40 pm 
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Quote:
2.13 GHz / 1.150V / 088 102 112 Watts / xx xx / FAIL

2.13 GHz / 1.325V / 100 115 126 Watts / 25 xx


Actually, you state here a 14W difference. I am most interested in the 6300 so i imagine it would be able to hit 1.15V stable at stock clock.

I have been wanting to build another htpc for my bedroom and I was wondering if this chip could be cooled passive with a pico psu. I need something with some serious speed to be able to do h.264 on my Westinghouse 37" 1080p LCD display. I think a X2 3600+ would handle this at 1.1V with Nvidia 6150 graphics or the new ATI R600 graphics (upgrade to discrete if needed) but the conroe is an interesting, faster alternative.


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PostPosted: Sun Aug 13, 2006 7:49 pm 
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autoboy wrote:
Actually, you state here a 14W difference. I am most interested in the 6300 so i imagine it would be able to hit 1.15V stable at stock clock.
We were talking at cross purposes but I’m with you now.
The E6400 was stable at 2 GHz @ 1.15 so an E6300 at its stock speed of 1.86 should be fine. I’ll go back and look at my notes later and see if I recorded the E6300 power consumption at 1.15V.


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PostPosted: Mon Aug 14, 2006 12:53 am 
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Thanks for doing all that testing SC, it's real nice to finally get some SPCR-relevant facts about Conroe. I especially was interested to see the lowest stock voltage in Speedstep, I couldn't find that in the Intel documentation. Good job! :wink:


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PostPosted: Mon Aug 14, 2006 3:57 am 
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jaganath wrote:
Thanks for doing all that testing SC.
No doubt there were loads of things I could have added and the one I’m kicking myself for is not seeing how fast I could run the CPU passively with the Ninja. It’s not particularly of interest to me which is why I forgot to run the test. Considering that the CPU temp under full load for 2 hours was only 12C over ambient at 2 GHz 1.15V with the Ninja running a Nexus at 600 RPM, it looks promising.

With regard to low power consuming motherboards, I was surprised to see that ASRock and Asus have boards with VIA (PT880 & P4M890) and older Intel chipsets (945G) that support Speedstep. They look promising for low power consumption and some support onboard VGA and even with DVI in one case.
The ASRock Conroe945G-DVI, apart from having a very descriptive name has an interesting spec: 945G chipset with GMA950 IGP and DVI, SATAII, DDRII, PCIe x16, PCI x2.

I’m not clear on the difference between Speedstep support and Enhanced Intel Speedstep Technology (EIST) support. Most of the boards I’ve seen only mention the former, although the Asus P5VD2-MX which uses the VIA P4M890 does indicate EIST support. My fear is that without EIST support you won’t be able to benefit from changing VCore using CrystalCPUID! Maybe one of the people who’ve bought the 775Dual-VSTA can report back on this issue.
These boards are going to have limited over-clocking potential I imagine, but if you aren’t interested in that anyway, they are very good value and the only current C2D boards with onboard VGA.

This report at Anandtech shows how little the performance difference is between PC3200 and PC2-6400 when using an E6300 at stock speed. The difference may well be larger when using a faster CPU or when overclocking the FSB. If you aren’t doing that then PC2-4300 (DDR2-533) is probably the lowest power consuming memory, provided that its voltage is set to 1.8V in the BIOS. If you use DDR-667 RAM, with some motherboards the voltage may be stuck at a higher voltage even if you run it with a setting of DDR-533.


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PostPosted: Mon Aug 14, 2006 5:05 am 
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What was the lowest voltage E6400 (and E6300) run stable with stock speed? What was the power consumption then?


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PostPosted: Mon Aug 14, 2006 8:53 am 
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Yeah, the 775Dual-VSTA is an interesting board. I would be able to reuse my DDR memory, saving money, with the option of upgrading to DDR2 if I wanted more memory. I could also use my 9600xt for now until someone releases a 7300GS with HDCP support. I don't think the boards' x4 pci-e graphics will slow down HTPC related stuff like it might for gaming. It is a very versitile board. It would really keep the upgrade costs down. If speedstep can get the voltage low enough so the processor is running less than 30W i will probably get one. I wish it could undervolt though.


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PostPosted: Mon Aug 14, 2006 9:21 am 
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paapaa wrote:
What was the lowest voltage E6400 (and E6300) run stable with stock speed? What was the power consumption then?
I did very little testing with the E6300 but if you extrapolate from the data posted above you’ll be able to estimate the power consumption to within 1W I think. Base your calculations on it being stable at 1.15V.
As for the lowest Vcore that the E6400 would run with at stock Speed, again you will have to extrapolate from the above data. It was stable at 2 GHz at 1.15V but not at 2.13 GHz, so it should only need a small increase to be stable at 2.13 GHz.

When I get access to more C2D motherboards I’ll focus more on the lowest stable voltage at stock speed. I was looking more at the over-clocking potential in my initial testing as I was trying to deduce the sweet spot for multiplier, FSB, VCore & RAM speeds values, as well determining the nature of Speedstep on these chips.

It’s dawned on me is that there is a way to get around the limitation with regard to booting with a FSB speed that is unstable until CrystalCPUID takes over the VCore setting. (See first post for details). Boot with a lower FSB value that is stable, wait until Windows has loaded and CrystalCPUID has raised the VCore at the lower Speedstep setting; then raise the FSB to the maximum that is stable at stock Vcore, with Clockgen or a similar utility. This way if you get a sweet C2D chip that is stable above 3 GHz at stock VCore, you can still use Speedstep. Your idle VCore will need to be raised above 1.15V, but it will still be a lot less than the 1.325V it would be using if Speedstep was disabled.


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PostPosted: Tue Aug 15, 2006 8:41 am 
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thanks a lot.

It's really a nice data/analysis that hardly found in other web.


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PostPosted: Tue Aug 15, 2006 12:05 pm 
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Great read.

Any idear how many W the Gigabyte GF6200TC is eating compared to a 845/965G (onboard gfx) ?


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PostPosted: Tue Aug 15, 2006 12:26 pm 
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dvdmonster wrote:
Any idear how many W the Gigabyte GF6200TC is eating compared to a 845/965G (onboard gfx) ?
I'm testing a couple of C2D boards with on-board graphics later in the week and will post results once I have them.


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PostPosted: Wed Aug 16, 2006 2:32 am 
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Also check out: http://www.xtremesystems.org/forums/sho ... p?t=111695

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PostPosted: Wed Aug 16, 2006 10:38 am 
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Poodle wrote:


Looks like the hunt for undervoltable boards is on again ...


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PostPosted: Sun Aug 20, 2006 6:22 am 
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Very good analysis, smilingcrow!

What exactly are the lowest and highest voltages you can set with CrystalCPUID? And what is the lowest multiplier? Could you also check these values using RMClock?

Considering the high default FSB of 266 MHz it is really sad that Intel chose 6 as the lowest multiplier one can use because that limits the overclocking potential for those who want to keep the lowest power consumption (read voltage) at idle.

Let's say you've got an E6300 and you want to overclock it but still keep the lowest power consumption at idle. Using 1.15V at the lowest multiplier of 6 would allow one to reach only 333 MHz on the FSB (= 2 GHz), which means only 2.33 GHz at the highest multiplier, which is sadly far from it's overclocking potential!

If that's true, then maybe it's better to buy the cheapest mobo that allows you to reach 333 MHz FSB and the cheapest memory that is able to cope with the resulting speed and invest the saved money in a CPU that allows for a higher multiplier, eg a E6400 or E6600...

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PostPosted: Sun Aug 20, 2006 2:03 pm 
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ZORAX wrote:
What exactly are the lowest and highest voltages you can set with CrystalCPUID? And what is the lowest multiplier? Could you also check these values using RMClock?
The lowest & highest VCore values selectable with RMClock & CrystalCPUID varied depending on the motherboard used, and this was when using the same CPU. I’m not sure, but this may be a difference between chipsets that support Speedstep and EIST (Enhanced Intel Speedstep Technology). The boards with the older chipsets support Speedstep and allowed a VCore no higher than 1.29V. The boards supporting the newer chipsets (975X & P965) went up to 1.325V. This obviously affects their ability to over-clock, irrespective of other variables. The lower VCore range was closer and they were all in the range 1.1xV
This idea is purely conjecture and I have no idea if it’s the real reason between the differences.

The multiplier could be manually set using RMClock with all boards and the limitation was that of the CPU being used. The E6400 could be set in the range 6, 7 or 8.

If you want both the absolute minimum idle power consumption and the maximum over-clock at stock VCore, then unfortunately you need the unlocked X6800. I think the E6400 & E6600 will offer a good trade off at a much lower price with the right motherboard. I’m just not sure that the right motherboard has been released yet. ATI may fill this gap.

After testing a number of C2D systems and a Core Duo desktop and laptop, I think the optimum system for low idle power consumption and efficient high end performance would be this:

A C2D mobile chip (Merom) in conjunction with a 945G (or other 945x chipset.).
The mobile chips run at a lower FSB than the desktop chips, but in the benchmarks that I’ve seen aren’t typically penalised by this in the performance stakes. The advantages are this:

The lower FSB consumes less power.
The 945G chipset is rated at 1066, which means that even a 50% over-clock leaves a Merom at 667 * 1.5 = 1000; less than a Conroe at stock.
The mobile CPUs idle at a lower frequency and allow a lower minimum VCore using RMClock. 0.095V on my laptop.
A Merom 2GHz even over-clocked to 3 GHz would still idle at only 1.5GHz with Speedstep. This is still less than a desktop chip that isn’t over-clocked; 1.6 GHz

I’m not aware of any S479 motherboard that uses this chipset; the Aopen S479 board that seems to be the only good over-clocking S479 board uses the power hungry 975X chipset. In power consumption terms, you lose more from the motherboard than you gain from the CPU.


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PostPosted: Sun Aug 20, 2006 9:57 pm 
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My results might not be typical, but my E6400 is rock solid stable at 1.1v overclocked to 2.712 Ghz. This is on a P5B Deluxe.


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PostPosted: Mon Aug 21, 2006 1:21 am 
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smilingcrow wrote:
I’m not aware of any S479 motherboard that uses this chipset; the Aopen S479 board that seems to be the only good over-clocking S479 board uses the power hungry 975X chipset. In power consumption terms, you lose more from the motherboard than you gain from the CPU.


Does this one have the chipset you mention?

http://www.abit.com.tw/page/uk/motherbo ... DEFTITLE=Y


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PostPosted: Mon Aug 21, 2006 2:15 am 
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Backslash wrote:
My results might not be typical, but my E6400 is rock solid stable at 1.1v overclocked to 2.712 Ghz. This is on a P5B Deluxe.

That’s impressive. How low does the P5B Deluxe go in the BIOS for VCore? When you say it is 1.1V, I assume that was set in the BIOS. Did you check the actual VCore in Windows, as it can differ quite a lot from what you set in the BIOS with some boards? Speedfan and CPU-Z are two commonly used tools that will show that.

I seem to have a below average E6400, as it can’t come anywhere near your settings and someone else posted running an E6400 at 2.13GHz @ 1.0V, which again I can’t match.
If this is the case, then it looks even more promising for over-clocking a C2D to a high level using RMClock and the stock VCore range.


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PostPosted: Mon Aug 21, 2006 8:54 am 
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Actually, my actual vcore is quite a bit lower than what I'm setting in BIOS. BIOS setting: 1.15v. Actual voltage according to CPU-Z, PC Probe, etc.: 1.1v.


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PostPosted: Fri Aug 25, 2006 7:35 am 
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Check out the Gigabyte 965P-DS3 if you are interested in undervolting. I am currently using one of these with BIOS F4, and it allows you to set the voltage all the way down to 0.51250! This is in 0.00625 steps too, so it's about as flexible as you can get.


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PostPosted: Fri Aug 25, 2006 7:54 am 
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Lloyd84 wrote:
Check out the Gigabyte 965P-DS3 if you are interested in undervolting. I am currently using one of these with BIOS F4, and it allows you to set the voltage all the way down to 0.51250! This is in 0.00625 steps too, so it's about as flexible as you can get.


C2D won't POST at 0.5125V though right? Anyone know what the lowest voltage is for it to POST?


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PostPosted: Fri Aug 25, 2006 4:03 pm 
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jaganath wrote:
C2D won't POST at 0.5125V though right? Anyone know what the lowest voltage is for it to POST?

The VID for C2D s 1.00000 (yes, five zeros). Some chips apparently still work quite a bit below that. YMWV.

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PostPosted: Tue Aug 29, 2006 10:52 am 
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I’ve posted these two reviews relating to C2D in the User Review forum:

Cooling a C2D with a Ninja (inc Fanless) & Katana.

Power Consumption of 5 C2D mobos with IGP & discrete VGA.


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PostPosted: Fri Sep 01, 2006 10:13 am 
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This guy managed to raise the VCore in the BIOS of a P5W DH Deluxe and still be able to use CrystalCPUID to change VCore settings. It only worked in a very rudimentary way in that he either had 1.05V or the voltage set in the BIOS, but that’s better than nothing. I’m speculating that he got it to work either because of using a different BIOS version or a different version of CrystalCPUID.


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PostPosted: Sun Jan 06, 2008 9:55 am 
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Joined: Sat Jan 05, 2008 8:52 pm
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new guy bumps an old thread...i stumbled across this site looking for undervolting options and love this site already..fyi, played around with undervolting and at 6400 stock fsb of 266 and memory at 400 (4 gigs of ram) no problem running the 6400 at 1.000 volts even. reads on 5 different monitor programs at between .99 or .992 on my gigabyte p35 ds4 and very stable. just for giggles, i went way lower, .75 volts and had to reset my cmos..may try .9 setting for fun, but i've already dropped my cpu temps from the stock at 1.3 from 41/42 idle-50-51C full load to 32/33 idle-40-41C full load going from 1.3 to 1 volts on the cpu. my case temp has dropped from about 34 at idle to 27@ idle. i'm thrilled..this is in an htpc system running 24/7 so while it's fun to have an overclock setting or 2 just for kicks saved in my bios, i'm quite happy to run stock for quiet/cool/reliable.


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PostPosted: Sun Jan 06, 2008 2:20 pm 
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Joined: Sun Oct 09, 2005 8:35 am
Posts: 1253
Location: Pleasanton, CA
A 6300 at stock is rated to run at 1.05V (the EIST low setting), so a 6400 at 1.0 is good, although not unexpected. You got a good chip.

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PostPosted: Sun Jan 06, 2008 2:28 pm 
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Joined: Sat Jan 05, 2008 8:52 pm
Posts: 26
ahhh, i didn't realize that with the EIST..must do some reading:) thanks...yeah, the sense i had otherwise is if you good undervolt decently and run stable that was one of the signs of a good one.


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