Overclockers attention! Running high VDIMM & low VCORE you risk to killing your CPU
 

Tony from OCZ has received some interesting inside information for the overclockers out there; he posted this at XtremeSystems forums

”What I will tell you is if AMD say this to me iI listen...and you should listen also:

If you run a high vdimm and a low vcore with E die (revE, aka venice, san diego, manchester, toledo, newark, lancaster, denmark, venus, ..) you are running the risk of killing the cpu's. So if you have OCZ VX (or others) and you are not raising the vcore on your cpu you stand a chance of pumping a lot of current into the memory controller and causing permenant damage.

Im seeing people running $1k cpu's at default vcore and BH5 at 3.4V, this is a sure way to kill the cpu and is NOTHING to do with an issue on the board. If you are going to run high vdimm run a higher vcore also, and keep your CPU's ok.

The newer CPUs run a much lower vcore, IE 1.4 or 1.35V. what you are looking at is the difference between the vcore and the VDD supplied to the memory controller from vdimm in bios. Now if the gap between the vcore and the VDD is huge you stand a chance of breaking down the diodes that protect the core from the high VDD.

All you have to do is strengthen the cpu's defences, you do this with a bump of vcore...thats all.”

Micutzu adds :

“The CPU doesn't have to do directly with the VDD, but with Vtt/Vref, wich should vary from 1.25 to 2V when you adjust the RAM from 2.5 to 4V. Maximum JEDEC Vdd voltage is 2.85V, and lowest voltage for A64 CPU's (CnQ activated) is 1.1V, so we know for sure that a difference of 0.325V between Vcore and Vtt is safe. This means that for a 1.35V Vcore voltage, we can have a safe Vdd of at least 3.35V, and for 1.5V Vcore -> 3.65V Vdd.

Probably the real danger is when those diodes go near the opening (conduction) voltage, wich should be ~0.6V for Si-based junction; if this is true, 1.35V Vcore and above 3.9V Vdd should kill the CPU instantly”

uOpt makes a nice reference table using the info provided by Micutzu :

“ETA: this is at default drive strength. Higher drive strength will require less differential for safety

Vdimm - Vcpu(min)
----------------------------
2.9 V --- 1.12 V (min)
3.0 V --- 1.17 V (min)
3.1 V --- 1.22 V (min)
3.2 V --- 1.28 V (min)
3.3 V --- 1.33 V (min)
3.4 V --- 1.37 V (min)
3.5 V --- 1.42 V (min)
3.6 V --- 1.47 V (min)
3.7 V --- 1.53 V (min)
3.8 V --- 1.58 V (min)
3.9 V --- 1.62 V (min)
4.0 V --- 1.67 V (min)

Absolutely NO WARRANTY for this.

And again, it is minimum safe CPU voltage based purely on the problem of voltage differential between CPU and RAM. The above table does not take any other voltage considerations into account. Or in other words: the voltage that is the minimum with regards to the Vdimm differential might already be over the upper limit of your CPU - and blow it up.”

You can read all about it here

good to know, but I started to panic for a sec when I first saw "vx", so I reread it :D

very, very important info


I guess another reason against cool and quiet.

Using CnQ and Overclocking is not done btw;)

You kill your VX instead of your cpu ;p

I can't believe the number of scary people at that forum;
and, the questions they raise from a simple table. Use with Extreme caution; if you are a pro (extreme), you know everything you do is taking a high risk :D

still waiting for my new set, don't know what ppl who don't got some spare ram must do when they have to RMA there ram



BTW: that table is quite ridiculous. Look at the Vdimm vs Vcore and you'll notice that it's quite normale you gonna need a certain Vcore when you reached your max mem speed at a certain Vdimm

Not much processors will go 9x310 (for a 3000+) with 1.4Vcore and the only thing you'll have to do is raise the Vdimm to 3.9V.
Offcourse you can go memory only overclock :)

Read this again and have no worry -

http://www.madshrimps.be/?action=getarticle&articID=325