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Help on E8400 voltages please

T

Technophobe

Limp Gawd
Joined
Feb 25, 2008
Messages
339
I want to overclock but not at all interested in running close to my max voltage for the CPU. Here is where the problem lies, getting the facts clear as to what value constitutes the max CPU voltage (Vcc) for my chip.

The E8400 box showed the following:

Batch: Q745A740
sSpec: SLAPL
Version: E27439-001
Pack Date: 01/21/2008
1.225V Max

The '1.225V max' - Is this the Vid rating for my particular chip? If so, then is CoreTemp ver 0.97.1 displaying the wrong Vid of '1.1125v'. My BIOS default auto settings give a Vcore of 1.225v (coincidence or reading the Vid from the BIOS at boot and adjusting to suit?).

The Intel datasheets have some complicated way of trying to give the max Vcc. First off they say Vcc absolute max is 1.45v but this, quote 'lies outside the functional limits of the processor'. So what is the functional limits... I read on. Vid range set at manufacture time can be between 0.85 and 1.3625v. Vcc min and max are differences from Vid (depending on current draw) as shown in a graph.

Then, if I read the graph right, at 0A Icc, Vcc max = Vid. At max Icc (75A - wow!), Vcc max = Vid - 0.105.

So, if my Vid is 1.225v (as maybe shown on the box), then my Vcc max at max load is 1.12v.
And if I believe CoreTemp's Vid of 1.1125v, then my Vcc max at max load is 1.0075 !! I think I would have some serious stability issues at this voltage !

I've already overclocked to 3.6GHz and have had to manually adjust the Vcore up to 1.26875 in BIOS to get it to run Prime95 reliably. Everest shows Vcore of 1.248v under load, so, if I've got my Vid right as above, I'm already overvolting my CPU by 0.128v !

This can't be right. I think I've gone wrong in my assumptions but I don't know where. I hope someone has been down this track before and can shed some light on the subject.

P.S. Wish I could go back and buy a E8400 with Vid rating of 0.85v - would solve my problems.
 
I didn't know anyone actually put that much thought into. 1.45v is what Intel is calling the max for these but they are also probably assuming you are using the stock cooler. You mention 0.128v like it's a lot of voltage, you do realize that is a tenth of a volt right? I would imagine a motherboard could easily overvolt that much or more even if you weren't overclocking and had settings on auto (like most non H readers). Seriously, keep it under 1.45v and I'm sure it will be fine, make sure the temps are ok too - however this is another issue. Mine never goes below 51 core temp, so I've got one with the stuck sensors... joy!

You won't be able to find one that has vid of less than 1.0 I know they are out there, but good luck finding an E8xxx series in stock anywhere.
 
I looked into this a lot when they first came out due to strange chip failures and followed up a month later.
It seems you are definitely safe if you remain below 1.3625V but above that you need to try and find the reports of failures to be sure.
After the initial failures, things dont seems as bad so either early samples werent as good or people have learned to be sensible with the new lower VCore :)
I cant provide proof of this (unless I go nuts finding it), but I dont delude myself so take that as you will.

http://www.xtremesystems.org/forums/forumdisplay.php?f=56 have a lot of people pushing these to the limit.
Be careful (especially at sites other than extremesystems) that anyone reporting very high VCore and speeds still has a working chip later.
Some people stop responding when they kill a chip.

I'm running at 1.387V @ 4GHz for about a month now with no detrimental effect and will be pushing it a bit harder soon if it remains stable for a few more weeks.
I have had 4.35GHz at 1.5V momentarily but quickly went back to safer voltages once I heard of the early failures.
 
I have an E8400 and my default voltage is also 1.225 like yours. I've been running at 4 GHz for several months now with the CPU voltage set to 1.325. With both cores loaded running Orthos, the CPU voltage drops to 1.280 but it is very stable, passing Orthos and Prime 95 stress tests.

With the CPU voltage set to 1.35, I can run it at 4.3 GHz but the CPU temps are into the mid-60's C running Orthos so I keep it at 4 GHz which is a good compromise between speed and heat.
 
I got my vcore @ 1.216 and its 100 % stable with anything thrown at it. anything below thats its not stable. I am @ 3.6ghz so im guessing with my small overclock it doesnt matter.
no orthos running- vcore= 1.216
orthos running- vcore- 1.192

100 % stable
 
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