Under voltage a CPU

[npoe1]

I want to know if there is a risk if I under voltage my CPU? A long time ago, somebody here told that there was a thread here in anandtech that was with some Intel engineers and they told them that if you over voltage your CPU you will damage it, no matter the temperature, so what effect have under voltage, I live in a very hot place so I don?t want my computer producing a lot of heat and my computer?s room sadly gets direct sun light it?s already isolate but there is a really big window. So what could happen beside of some instability?

My processor is a A64 3000+ Venice.

 

[dguy6789]

Quite simply, the lower your cpu voltage, the better. Lower voltage means that your cpu will use less power, generate less heat, and live longer. If you are not overclocking, run at the lowest possible voltage that your processor can remain stable in. Prime 95 is a good test for stability.

 

[Zap]

One thing to beware of is that if you use A64 and you have your CPU undervolted and RAM overvolted, you can kill your CPU.

I have three systems that are undervolted. One of my notebooks with a Dothan CPU, my server with a Pentium 4 M in a desktop board and a socket 754 Sempron in my HTPC. For the notebook I wanted longer battery life. For the others, just less power draw, less heat, less noise.

 

[orangat]

Originally posted by: Zap
One thing to beware of is that if you use A64 and you have your CPU undervolted and RAM overvolted, you can kill your CPU.
.......

Can you explain why?

 

[Zap]

IIRC...

I think it may have been either Xtreme Systems forums or DFI Street. People were finding that their A64 CPUs were dying. Someone theorized that it was the voltage difference because the high voltage RAM feeds directly into the CPU, and dared people to try (without even overclocking) severely undervolting their CPU and severely overvolting their RAM. Well, some people tried it and the result was the CPU dying in short order, some after a couple of reboots.

 

[npoe1]

So, to be safe it?s better to use voltage in RAM like stock and undervolting the CPU, so there should no be side effect? And is this problem just with Athlons or could it apply to Intel?s side?

 

[TekDemon]

Well I wasn't aware of this development but I went and read up a little at xtreme systems and a poster (high5) said:
"there was a general consensus that safe Vcore limit is Vdimm/2 - 0.325V."
And another poster (creidiki) said:
"So long as your VDIMM is within JDEC specs (i believe up to 2.7) you can go down to lowest C'n'C voltage... is that 0.95v? 0.9v? Im not sure, but that's your safe margin for the voltage differential betwen the mem controller and main core... check the sticky for info."

Which makes sense, since whatever the CPU normally undervolts to would have to be a safe voltage for all JDEC spec'ed memory voltages or stock systems would be dying all the time (I think creidiki meant to type C'n'Q for Cool and Quiet).

Anyways I'm guessing whatever power circuitry there is between the memory and the CPU can't really handle too huge of a voltage difference before the voltage just runs over from the memory, so this might actually vary depending on what kind of motherboard/chipset you're running. Like, maybe the chipset will prevent power leaks so long as the voltage difference is under a certain amount (since voltage is after all a measure of electrical "pressure") but if the voltage difference is too huge then the pressure just kinda makes the electricity go right through. I didn't think this would actually happen but I guess it's somewhat plausible.

I finally found the original thread over at XS:
http://www.xtremesystems.org/forums/showthread.php?t=79509

OOOOH it's because the memory controller on A64's is integrated into the chip itself!!! Haha I totally forgot that, the voltage from the memory doesn't need to jump through any chipsets-the memory is already talking to the CPU (apparently at 1/2 VDimm).

Heh I guess that means Conroe will be immune to this since it doesn't have an on-die memory controller...yay undervolting all the way!

 

[Kakumba]

Yeah, you got it. The mem controller is indeed why its dangerous. however, I dont think anyone undervolting their CPU is likely to be running over 3 volts on their RAM...

Anyways, undervolt as much as you can.

 

[Zap]

Originally posted by: TekDemon
I finally found the original thread over at XS:
http://www.xtremesystems.org/forums/showthread.php?t=79509

Thanks. I knew I wasn't imagining things. I leave that for... things other than computers.