People often confuse the diff between bios set vcore and what bios loads at as vdroop, but it isnt. The diff is known as voffset and is commonly refered to as vdrop. This is built into every board as a safety feature as specified by Intel. Here is a pic to illustrate:
Vdroop is the voltage drop when the CPU is under load,. You can see this by opening CPU-Z at idle then noting the voltge drop when stressing the CPU by running Prime95.
Here is an article that explains voffset (vdrop), vdroop and the effects of Loadline calibration (LLC) and the pencil vdroop mod (essentially what LLC is):
Anandtech: LLC
Quote:
Originally Posted by t_russell
Voltage will never spike under load it will droop further than the drop point. 1.4v BIOS = 1.38v windows idle (drop) = 1.32 windows load (droop).
It is the transition from loaded to unloaded where the spikes occur this is the reason for the drop and the droop. If you set 1.4v in BIOS your PROC will never see higher than 1.4v but is unlikely ever to see even 1.4 for more than a few milliseconds.
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As t_russell said, here is what is happening with your voltage when the vdroop is eliminated, which illustrates the effects of voltage spikes:
Quote:
No Vdroop means the VRM circuit must work harder at maintaining a constant voltage
In this next case we eliminate Vdroop altogether and examine the chaos that ensues. As illustrated by our model, removing Vdroop does nothing to reduce the magnitude of the idle to full-load transient but does increase the settling time as the VRM must recover to a higher final regulation voltage. As in the case of no Voffset, it is possible to exceed the maximum allowable CPU voltage (VID). Clearly, removing Vdroop gains us nothing and only serves to create problems that are more serious.
So what happens when we remove both Voffset and Vdroop? The answer is simple - bad things. Although the difference between the maximum positive and negative peak overshoot are the same, severe violations to the CPU VID limit occur. If you're asking yourself what's the problem with this, consider the case of a CPU VID of 1.60000V - because the user feels this is the absolute maximum CPU voltage that they will allow. Just how high do you think CPU voltage will go after leaving a heavy load condition? We can't be sure without knowing more of the details, but we can certainly conclude that it will be well in excess of 1.6V. If you've ever run a benchmark only to have your system crash right as it finishes then you have experienced the consequences of this poor setup.
Finally, let's take one last real-world look at the consequences of removing Vdroop. ASUS' implementation of this feature, labeled as Load Line Calibration and included with their latest line of motherboards, is particularly worthy of our attention for a number of reasons. The first is that setting lower voltages with this option enabled actually results in a condition in which the CPU voltage under load is higher than the idle voltage. Imagine our confusion as we desperately struggle to understand why our system is Prime95 stable for days yet continues to crash under absolutely no load. What's more, in spite of the absence of droop and for reasons unknown, enabling this feature artificially raises our CPU's minimum stable core voltage at 4.0GHz from 1.28V to about 1.33V. As a result, our system uses more power under load than is otherwise necessary. Our efforts to reduce our processor's supply voltage backfired - instead of lowering the system's total power consumption we managed to affect a 20W increase.
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While this voltage spike doesnt seem to affect 65nm CPUs which have a higher voltage tolerance, they do affect the 45nm CPUs. I've seen people kill their 45nm CPUs when running max vcore and enabling loadline calibration. The voltage spikes are just too much for the 45nm core to take.
Voltages lower in windows than in BIOS?
01-19-09
