Trädvy Permalänk
Nov 2008

Övervolta CPU, guideline och risker!

Har läst ganska mycket om detta ämne då jag satte lite höga mål för min överklockning och började smått oroa mig för höga värden och dess effekt. Stötte på en tråd som hade riktigt hjälpsam information. Intressant och informativ läsning, bör också sätta stop på frågor angående folks "safe" Vcore och dylikt. Visserligen gammal tråd men väldigt bra skrivet och kan tycka att det är väldigt relevant när man ska pusha sin hårdvara.


One remarkably common misconception about overvoltage, is that there is a number set in stone for each particular component, a number which dictates the "safe" overvolt that one can use with any specific piece of hardware. This is not true.

It is partially valid however. Specific types of hardware are almost always similar in their limits, granted no manufacturing defects. However, each piece of hardware is still unique to small, varying degrees. Being able to find your individual hardware’s unique "safe" voltage limit is useful, when squeezing every last reliable speed step-up out of our of your hardware.

When we overvolt, we rely on the integrity of our hardware. We assume that it is of high quality, without manufacturing defects, and that it is capable of withstanding a large overvolt without sustaining damage. Most of the time, this is the case. There are always exceptions. It is speculated that hardware which is damaged through overvolting, already contained small defects or weaknesses that were only made apparent, or made worse, when the hardware becomes strained through overclocking, and overvolting. There is no accurate way to tell if your specific piece of hardware has such flaws. Sometimes, we get unlucky. For the most part though, ‘healthy’ hardware is capable of running smoothly for years and years with a considerable overvolt in place.

Overvolting is dangerous, and inherently risky. As soon as you overvolt your computer hardware, you void your hardware’s warranty, and run the risk of sudden hardware death. That risk is small if you are cautious and smart with your overvolting, but it is always present nonetheless. The words overvolt and safe should really never be used in the same sentence. For this guide, I will refrain from saying safe, and will use "safe" instead – there are always risks, make no mistake.

Speaking from a personal perspective, I have overvolted almost every single piece of transistor-based and overclockable hardware that I have ever owned. I have never had a hardware death as a result of overvoltage (although I have killed more than my fair share of computer hardware...), and barring bad luck, you shouldn’t either if you take your time, and are careful.

More voltage has the nasty side effect of creating heat. Our transistor based computer hardware does not do well with high temperatures, and can sustain damage from lengthy exposure to high temperatures. The "safe" temperature to run our hardware at is theoretically directly related to how much voltage you are giving your hardware – the larger the overvolt, the cooler you should be keeping your hardware in theory. There is certainly no number or ratio set in stone for this – common sense is your only reliable ally – "if it’s stable it’s safe" is an excellent guideline. Stability is a reliable and consistant standard to use for the measurement of safety, which is not a "variable" that is measureable directly.

Overvolting also has the effect of increasing the rate of electromigration within our hardware - both high current density and high levels of heat will accellerate the rate of electromigration (and both of these variables are directly increased through overvoltage).

Electromigration increases the resistance of the metal interconnects (miniscule wires and contacts - the conductive signal pathways inside of our transistor-based processors and memory) within our transistor-based hardware, which can mess up processor operation. Remember the transistor tolerances mentioned in the first section (If you didn't read the first section, don't sweat it)? When signal resistances within our transistor-based hardware are increased, our signal strength can fall outside of our hardware's transistor VDD tolerence as a result. Electromigration can also eventually cause interconnects to break entirely - and a broken interconnect pretty much means a dead piece of hardware (you cannot send a voltage high signal down a broken interconnect!). Electromigration is a long-term issue, an increased rate of electromigration means a shorter lifespan for your hardware. Electromigration is not a huge issue with modern hardware due to the high quality of the materials used in the construction of (most) modern hardware - although it apparantly does still occur, albeit at a slower rate.

When overvolting, it is important that one has adequate cooling on their hardware. A good rule of thumb is "voltage doesn’t kill hardware, heat kills hardware" (and likewise, "overclocking doesn't kill hardware, heat kills hardware"). This simple rule, of course, is only applicable if one overvolts their hardware within reason, "reason" being actively paying attention to what your hardware tells you through its responses to overvoltage.

All the doom and gloom done with, lets move on to our last and most interesting section of the guide, Overvolting Technique in Overclocking.

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Teknik för övervoltning:

"1.8V is the maximum safe 24/7 overvolt for your processor."

I see this, or comments like it, quite a lot. It is a common misconception that each specific type of hardware has a set-in-stone overvolt that one cannot safely exceed. This is very much untrue. No two processors are alike. Just as two ‘sibling’ processors coded one digit apart in their batch will overclock to different levels, those two ‘sibling’ processors will react differently to overvoltage.

Our hardware is unique, and needs to be treated uniquely, on a case-by-case basis. Going about this is actually quite easy, and very simple, if somewhat time consuming.

It’s all about two things. Stability, and Diminishing Returns. These two factors are the holy grails of overvolting. By paying attention to both, we can chart out and determine our specific and unique hardware’s unique "safe" 24/7 overvoltage limit.

Please keep in mind that the following is to be used as a guideline; those who are adventurous or suicidal, and those who are cautious, may respectively choose to adjust the following technique to suit their personal comfort levels. The following technique is independant of temperature and cooling – temperature is a variable which directly leads to both Diminishing returns and Instability, and as such it is taken into account, although indirectly. I am in no position to tell anyone specifically what is a "safe" temperature to run their hardware at. However, thorough use of the following guidelines will invariably leave you at a "safe" temperature by default.

First off, lets see how high we can overclock our piece of hardware, with some degree of overclock stability, using stock voltage – no overvolts just yet. Thorough stability testing is not really necessary at this point, as we are only doing some preliminary probing into our hardware’s capabilities. A quarter hour run of Prime95 or a similar stress testing program for a processor, a quarter hour run of 3DMark for a GPU/GDDR, or a quarter hour run of memtest86 test #5 for memory, is sufficient at this stage.

~ Scale your clock frequency higher in small steps. For modern processors, ~100 MHz steps are appropriate. For modern RAM, ~10 MHz steps are appropriate. For modern GPUs/GDDR, ~15 MHz steps are appropriate. The step size is not particularly important.
~ After each speed ‘step’, run a quick stability test to make sure that your overclock has some integrity.
~ When you get to the point where stability is compromised, begin to ‘fine-tune’ the overclock. Drop your speed step size, and find a rough stable overclock limit.
~ Write down the ‘final’ overclock, and the stock voltage used.

Now that we’ve done some initial probing, we can heat things up a little bit, and add some voltage. Overvolt the hardware in question by the minimum voltage increment available in the BIOS, likely 0.025V for processors, and 0.025V-0.1V for memory. If you are overvolting through use of a physical voltage modification, keep to tiny 0.025V overvolt steps. The smaller the voltage step, the more accurate our findings will be, the more time consuming the process.

~ Starting from the clockspeed we left off at after testing at stock voltages, ‘fine tune’ the frequency upwards in small steps, as before.
~ After each step, run a quick stability test to check for overclock integrity.
~ Continue untill you lose stability.
~ Once stability has been compromised, fine-tune the overclock to the absolute limit point where it can run with stability for 15 minutes.
~ Write down this rough ‘final’ overclock, and the voltage used.

We now continue with the above steps, incrementally increasing our overvoltage, and charting out the clockspeed gains which we see at each overvoltage step – go until you have completed four steps, including stock voltage. This will take some time, but it’s worth it.

After four voltage and clockspeed steps, it is time to start a graph. A piece of graph paper and a pencil, or graphing software, are all you need to do this. A chart with "VOLTAGE" for the horizontal X axis, and "CLOCKSPEED" for the vertical Y axis is appropriate. Use stock voltage as the voltage starting point, and the maximum rough stable overclock at stock voltage as your clockspeed starting point.

Chart out your results thus far. Can you see a curve yet? After four small incremental voltage and clockspeed ‘steps’, we start to get an idea of how our hardware is reacting to overvolts. Some hardware will already start to peak after four steps. Other hardware is just getting started, hungry for more. Every piece of hardware is different, which is why this graph is so important – on a piece of paper your hardware’s unique reactions to overvoltage are fully outlined.

Right now is where we need to start paying attention to our gains, looking for diminishing returns. This isn’t too difficult with a graph right in front of us! When your curve begins to taper off, and flatten out, diminishing stable MHz returns per mV overvolt have kicked in. This is a good point to stop overvolting, when looking for a "safe" 24/7 overvolt and overclock.

Keeping an eye on your graph as you go, continue upwards in small overvoltage and clockspeed steps, until such a plateau becomes apparent on your graph. At this point of diminishing return, we can 'fine tune' our overclock for stability, for 24/7 use. Below, I have attached a sample graph, outlining this peak with a fictional (and conveniently clear) example.

Going slightly past the point of diminishing returns is certainly not "wrong", although the risks of both long term and short term hardware damage increase significantly when once does so. For hardcore benchmarking, suicide screenshots, and crazy fun, the graph is somewhat irrelevant. The graph guideline is an excellent tool for finding a "safe" 24/7 overclock/overvolt for your unique hardware, it is not so useful for the benchmarker or record breaker.

If your hardware sees stable MHz gains from seemingly large overvolts without peaking, do not be afraid to continue. Your hardware will tell you when it has hit its limits – it will peak or become unstable. High temperatures will directly cause both of these situations.

Overvolting far past dimishing returns will take one to the point where the negative impact of increased temperature as a result of voltage, will outweigh any gains from overvoltage in the first place. The curve will start to head downwards. When one gets to this point, they have entered the ‘death zone’.

I hope that this guide will prove useful to some of you. Please remember that all of this is merely guideline, not law - not even approaching it. It is one possible method of finding "safe" overvoltage limits, one which I have found to be extremely effective, safe, and efficient through personal experience.

Keep in mind however, that this technique is thorough and "safe", in the sense that it is based off of your unique hardware’s reactions to overvoltage. I strongly believe that this technique for finding your hardware's overvolt limit is as good as any other out there.

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