In the Forums...
Posted: July 20, 2000
Written by: Dan "Tweak Monkey" Kennedy
CPU Core Voltage
There are a couple different voltage levels of a CPU, but the important one that I'll be talking about is core voltage. Tweaking the core voltage is by far one of the best techniques to achieving a higher clock speed.
How important is voltage to overclocking? Well, since this varies on every system, I'll use my last CPU as an example. It was a Celeron II 566 (8.5 x 66 MHz bus default) that ran at 1.5 volts. When I first received this CPU, I immediately put it into my Abit BF6 motherboard and proceeded to overclock it. With the default 1.5 volts, the CPU could not make it over 620 MHz without crashing. So I put the voltage up to 1.6. Now it ran all the way up to 706 MHz without crashing. However, at 1.6 volts it would crash if I set it higher. So I put it to 1.7 volts and hoped for the best. Sure enough, I managed to hit 808 MHz without problems. I had heard that many people with Celeron II 566 CPUs could hit 850 no problem. So I tried 1.75 volts. Sure enough, it hit 850 without problems. At 1.75 volts it refused to go farther, though. At 1.8 volts I managed 876 MHz. I dropped it back to 1.75v @ 850, however, because of heat issues.
There are a couple simple rules I abide by when tweaking the voltage of a CPU:
1) Voltage = Heat - Higher voltage obviously means more heat. Higher voltage may allow you to overclock a CPU higher, but without proper cooling, the PC will freeze or have other problems farther down the road.
2) .3 Volts over Default; MAXIMUM! - It's a bit conservative for some users, but I rarely push a CPU higher than .3 volts over the default setting. Not only will it create more heat, but it could possibly damage the CPU. If you want to push your CPU higher, go for it. Just remember, I don't recommend it. Also, make sure you don't accidently jumper a slocket or a motherboard for something like two volts over the default value. This could result in instant death for your CPU.
One of the most publicized issues with overclocking is the heat. Increasing the clock speed of a CPU will just about always result in more heat. And increasing the voltage does the same... so increasing the clock speed and voltage can lead to insane heat levels, far beyond what the CPU is normally used to dealing with. But that shouldn't be too much of an issue for mild overclocking, since generally, CPUs run at far below their maximum stable temperature. In general, a CPU should be relatively stable so long as the temperature is below 115ºF. Anything over that could lead to instability on certain CPUs. Some systems can be fine way up to 140 or even 160ºF, but for the most part, try to keep the CPU below 115ºF.
If your overclocked PC freezes after several minutes or longer, chances are you need better cooling. Before you spend any money consider the free options available to you:
1) Cool room = Cool PC technique - If you live in a house with air conditioning that's constantly being run or your room temperature is far lower than your system's temperature, you can probably rid most of your heat problems by removing the side panels to your case. If your room is 70ºF, the air outside your case is probably much cooler than the air inside your case. So remove the panels and you can probably drop the temperature signficantly. Also, try to keep the PC's area well ventilated.
2) Software cooling - Some people are skeptical of software cooling's effectiveness, but I have seen very good results. CPUIdle has always been my favorite software cooling utility. On my Celeron 566@850 system, the temperature dropped from 110ºF to 95ºF in a 30 minute period.
3) More fans / Cooling - No, this option isn't free, but usually it's cost effective to buy fans to cool your PC if you've got a highly overclocked CPU. Consider something that will cool your whole PC, such as The Card Cooler XT. Make sure to have exhaust and intake (hot air going out and cool air coming in) in effective locations. Usually you'll want exhaust near the top of your PC since the heat will rise in a tower case. The intake should probably be near the bottom of the case, since the coolest air in the room is probably close to the floor, especially if it isn't carpeted. :)
Consider a better CPU cooler as well if you think the price is worth the overclocked speed you've achieved. Golden Orbs, Alphas, and typical "big ass fan/heatsink" combos work very well to remove heat from CPUs.