# Undervolted Xeon



## Vario (Aug 2, 2013)

-.165 offset, 20 Loops IBT at near max ram, cpu at 3.5 stock speed, with a load voltage of merely .876!


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## Vario (Aug 2, 2013)

Small fft








Are there any issues running a large undervolt like this, particularly if the card draws more current due to less voltage?


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## McSteel (Aug 2, 2013)

It doesn't draw more current. It draws less power due to lower leakage. If you could simply scale voltage down to any point and the only drawback was increased current, so as to satisfy constant power draw, everyone would run at 0.5V or less...

You just stumbled upon a particularly good, low-leakage chip. I'd hold onto it if I were you.


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## Vario (Aug 2, 2013)

McSteel said:


> It doesn't draw more current. It draws less power due to lower leakage. If you could simply scale voltage down to any point and the only drawback was increased current, so as to satisfy constant power draw, everyone would run at 0.5V or less...
> 
> You just stumbled upon a particularly good, low-leakage chip. I'd hold onto it if I were you.



Okay my thinking was just Power (w) = current (a)* voltage (v), if voltage reduced current might increase if wattage reported is still 50w.  Thanks for the clarification...

With undervolting, load temperatures have been reduced from 70*C to 55*C (average across cores) in intel burn test   this indicates that power consumed MUST be lower  so both voltage and current are down.


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## Mussels (Aug 2, 2013)

amp281 said:


> Okay my thinking was just Power (w) = current (a)* voltage (v), if voltage reduced current might increase if wattage reported is still 50w.  Thanks for the clarification...
> 
> With undervolting, load temperatures have been reduced from 70*C to 55*C (average across cores) in intel burn test   this indicates that power consumed MUST be lower  so both voltage and current are down.



this reported wattage you speak of, was probably incorrect. measure the PC at the wall to see the actual power usage drop.


undervolting is good. one day as the hardware/PSU weakens it may become unstable again and need slightly higher voltages, but i always undervolt my CPU's on day 1 to see how cold they can run at stock (and then i OC them as high as i can at stock volts )


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## Vario (Aug 5, 2013)

So ended up at a -.15 volt offset, and after 3.5 days of testing, I have passed 12 hours of IBT max, 24 hours of small fft, 24 hours of large, and 24 hours of blend p95.  100% max load is 51°c at a max of .888 volts .  P95 didn't like a mere .876 volts after about 12 hours, so I bumped the offset back up from a low of -.180 (that passed IBT no problem) to -.150 (100% stable as far as I can tell).

I wish this thing could be overclocked.  This chip would have made a stellar 3770k.  I am NOT gonna mess with the base clock, don't want to ruin my pci-e...


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## Vario (Aug 6, 2013)

Googled CPU test software to see about some alternatives to P95, OCCT ,and IBT and I found this insightful post by a *Tom's CPU Expert*. Tom's hardware truly is the best tech forum on the web.  This man must be a Computer Engineer for a leading microchip company, as he is a *CPU EXPERT*


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## Frick (Aug 6, 2013)

A stress test that does not ... stress the CPU?


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## EarthDog (Aug 6, 2013)

amp281 said:


> Googled CPU test software to see about some alternatives to P95, OCCT ,and IBT and I found this insightful post by a *Tom's CPU Expert*. Tom's hardware truly is the best tech forum on the web.  This man must be a Computer Engineer for a leading microchip company, as he is a *CPU EXPERT*
> 
> http://i.imgur.com/o2qwhL2.jpg


LOL @ Tom's being the best on the web... wow. Its just too big for me. Too many people that THINK they know what they are talking about and don't. Occasionally you will find a gem here there and everywhere but, best... oof, not IMHO.


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## BiggieShady (Aug 6, 2013)

His cpu is hitting 100 celsius in prime, but he wants a stress test that produces real heat .... yeah


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## CounterZeus (Aug 6, 2013)

amp281 said:


> Okay my thinking was just Power (w) = current (a)* voltage (v), if voltage reduced current might increase if wattage reported is still 50w.  Thanks for the clarification...
> 
> With undervolting, load temperatures have been reduced from 70*C to 55*C (average across cores) in intel burn test   this indicates that power consumed MUST be lower  so both voltage and current are down.



The correct formula for a CPU is
P = 0.5*a*f*C*V_cc^2 + I_l*V_t + a*f*I_sc*V_t

0.5*a*f*C*V_cc^2  -> active power, with 'a' amount of capacitors/gates active and C the capacity of them

I_l*V_t -> leakage power

a*f*I_sc*V_t -> short circuit power


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## Vario (Aug 6, 2013)

Whats the risk on Ivy if I bump my fsb a tiny bit?


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## EarthDog (Aug 6, 2013)

BCLK, not FSB.

Same as any other... You have a bit of headroom (1-5BCLK)


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## Vario (Aug 6, 2013)

EarthDog said:


> BCLK, not FSB.
> 
> Same as any other... You have a bit of headroom (1-5BCLK)



Yeah BCLCK, I'm used to old AMDs.  Might give it a shot.  With OCCT and my case fans on medium, I am getting only 49*C load temperature!

Would a +5 to BCLK kill my GPU or anything?


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## EarthDog (Aug 6, 2013)

AMD was HTT. Intel was FSB... but yeah.

It shouldnt. Every CPU is different in how much it can take. Try it.


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## Aquinus (Aug 6, 2013)

amp281 said:


> Would a  5 to BCLK kill my GPU or anything?



Bumping the BCLK doesn't tend to kill much of anything, but it will cause anything on the CPU PCI-E root hub to have issues if you push it up too high since skt1155 CPUs (including the Xeons,) have the PCI-E clock tied to the BCLK. PCI-E usually doesn't take too kindly to being overclocked which is one of the reasons why you can't get the BCLK higher.

SB-E will use BCLK Straps to adjust the PCI-E clock domain and the BCLK to keep it stable which is why at any given strap, SB-E still doesn't overclock higher than 5Mhz (for example, 132Mhz is the absolute highest I can get my BCLK to run on the 125Mhz strap and 107Mhz on 100Mhz strap.

I think Haswell has an external clock gen for PCI-E though, but I could be wrong.


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## Vario (Aug 6, 2013)

Aquinus said:


> Bumping the BCLK doesn't tend to kill much of anything, but it will cause anything on the CPU PCI-E root hub to have issues if you push it up too high since skt1155 CPUs (including the Xeons,) have the PCI-E clock tied to the BCLK. PCI-E usually doesn't take too kindly to being overclocked which is one of the reasons why you can't get the BCLK higher.
> 
> SB-E will use BCLK Straps to adjust the PCI-E clock domain and the BCLK to keep it stable which is why at any given strap, SB-E still doesn't overclock higher than 5Mhz (for example, 132Mhz is the absolute highest I can get my BCLK to run on the 125Mhz strap and 107Mhz on 100Mhz strap.
> 
> I think Haswell has an external clock gen for PCI-E though, but I could be wrong.



Cool good info.  I am glad to hear it won't kill the GPU.  This 7970 would be a pain $$$ to replace.  I bumped to 103 and the extra 100mhz is pretty cool.  Now at 3.6 (two free bins are allowed on this chip (33 goes to 35).  Voltage is still just .888 and my IBT very high temp is a mere 52 degrees.  These Xeons are awesome!

edit2: it made this BOOP noise whenever I moved a window around while IBT was running with the 103 bclk, not going to mess any further with it and reduced it back to 100.


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## Mussels (Aug 7, 2013)

amp281 said:


> Cool good info.  I am glad to hear it won't kill the GPU.  This 7970 would be a pain $$$ to replace.  I bumped to 103 and the extra 100mhz is pretty cool.  Now at 3.6 (two free bins are allowed on this chip (33 goes to 35).  Voltage is still just .888 and my IBT very high temp is a mere 52 degrees.  These Xeons are awesome!
> 
> edit2: it made this BOOP noise whenever I moved a window around while IBT was running with the 103 bclk, not going to mess any further with it and reduced it back to 100.



that noise was probably the system lagging. if you lower IBT's priority in task manager, it shouldnt happen.


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## Vario (Aug 7, 2013)

Mussels said:


> that noise was probably the system lagging. if you lower IBT's priority in task manager, it shouldnt happen.



Okay, I've never heard that before with IBT though and I have run IBT for 12 hours before while multitasking other stuff.


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