Modified from http://www6.tomshardware.com/guides/overclocking/index.html by Wattana Rattanaprom

What Is Overclocking?

The term 'overclocking' describes the process of running your CPU at a clock and/or bus speed that the CPU hasn't been specified for - logically, that speed is usually higher.

The tempting idea behind overclocking is to increase system performance at very little cost. In many cases you only need to change a few settings on your motherboard to make your system run faster. In other cases you only have to add a few components (usually for cooling) to achieve the performance increase.

In the past, overclocking was usually nothing more than increasing a CPU's clock speed to that of the next higher model, e.g. a Pentium 120 to a Pentium 133. Now, with new bus speeds available on several motherboards, you can change the clock and bus speed of a CPU to values that don't officially exist. This new way of overclocking is yielding an even higher performance increase than the classic one. It even gives you the ability to increase the performance of the fastest model of a particular CPU production line (e.g. P200 to 250 MHz, PPro 200 to 233 Mhz).

Although there are millions of tales of damaged CPUs and other system components, in most cases overclocking is completely harmless. There are, however, a few things to take into consideration.

• Your CPU could be damaged by so-called 'electromigration'. Electromigration takes place on the actual silicon chip of your CPU in areas which operate at a very high temperature, and can cause permanent damage to the chip. Before you start to panic, you should first realize a few things. CPUs are designed to run at temperatures between -25 and 80 degrees Celsius. To give you an idea, 80 degrees Celsius is a temperature that nobody is able to touch for longer than 1/10 second. I have never come across a CPU at this temperature. There are plenty of ways to keep the CPU case at less than 50 degrees Celsius which increases the probability of keeping the chip inside at less than 80 degrees. Also, electromigration does not immediately damage your chip. It is a slow process, which more or less shortens the life span of a CPU running at a very high temperature. A normal CPU is meant to live for about 10 years. However, in ten years nobody is going to be using a CPU with today's technology. I won't even use my CPU anymore in 2 months. If you want to be kept free from this electromigration scare, you have to do as much as possible to cool the CPU. Cooling is the Numero Uno Oncho in overclocking!!! Never ever forget that!

These terms don't necessarily apply for Cyrix, IBM, and AMD CPUs. Because of the already high rate of heat production at their original clock rate, you must work extra hard to keep them cool in overclocked conditions. I've come across several dead Cyrix 6x86 CPUs so far, so be careful or just let it be!
• Nobody likes system crashes or hangs, but in a professional business environment, avoiding a system crash or hang can be most crucial. It certainly is a fact that you are increasing the probability of system faults by overclocking your CPU. But this is only the probability !! If you have just overclocked your system and the first thing you do is use it to start writing your dissertation, don't be surprised if a system crash occurs which causes you to lose all your data. After finishing the overclocking process you have to put your system through a tough and thorough testing procedure. If the system passes all the testing, only then can you talk of successful overclocking and feel confident everything is working well. I'm using Winstone and the BAPCo Suite for reliability testing. You may not have the BAPCo, but it certainly is worth getting the new Winstone 97.
• The third debate against overclocking is that your father, brother, best friend, neighbour, or boss thinks it's immoral. Well, I always enjoyed living in sin, but if you've got problems with that, read the next chapter.

My dear visitors, I can tell you that I have come across a lot of animosities from the really straight-up type of law book fellows who have told me how irresponsible and immoral my website is. There are quite a few different ways to respond to this topic:

• If you are unwilling or afraid to overclock your CPU, there is no reason to annoy other people with your opinion. Just because the CPU manufacturers have an opinion on overclocking does not make it the right one. People who are overclocking their CPUs appreciate and respect this point of view, but choose to see it differently and are benefiting from their opinion. As long as there is no sentence against overclocking, we are not doing anything against the law and hence there is no pleasure in denunciation. Period!
• It is also fairly questionable if there actually is a difference between Pentium chips with different official clock speeds. The best example of this is the P150 and the P166. Isn't it strange, that all P150s are standard voltage chips and almost all P166s are VRE voltage chips? Doesn't it sound like Intel is using the same chip in both of them, but it only runs stable enough at 166 MHz with VRE voltage. Intel is selling the P150 only to satisfy the market and probably gets a good chuckle at the stupidity of the general public who don't realize this.
• In Europe there are a lot remarked Pentium chips around, as recently discovered when all over Europe there were several concurrent razzias against criminal organizations that re-marked thousands of P133s to P166. The proud owners of these CPUs are convinced they have a real P166, just because it's written on the chip. Do you think such things do not occur in the US? Hahaha!! I'm wondering how many people own faked P166s, who would NEVER overclock their CPU! Isn't that a funny thought? Did you know that Intel isn't interested in marking their chips reliably via a software readout at all? As long as they sell enough chips, they don't mind the re-marking of Pentiums. They even tried to avoid the publication of the recent events in Europe and I bet hardly anybody in the US ever heard about that.
• The main idea behind sensible overclocking is simply to use your brain, which brings me back to my 'car driving' introduction. If you want to successfully overclock your system without any loss in reliability, you will have to take care of proper cooling, do decent testing, and stay within the bounds of common sense. Don't try to overclock a P100 to 200 Mhz or anything crazy like that. Just use your brain!
• Is smoking immoral?

Well, so far I've only talked about Intel CPUs. These CPUs are in the majority, but there are also CPUs from Cyrix, IBM and AMD. What about overclocking these?
Because Cyrix, IBM, and AMD have always lagged behind Intel and its Pentium CPUs in terms of performance, they have had to release their CPUs at the highest possible specifications. When Intel produces a Pentium silicon chip, they are not as concerned if it can run at 166 or 200 Mhz. Because of its design and the high production rate, there will be enough chips which run at both 166 and 200 MHz. Also Intel was the first mainstream CPU manufacturer for PCs that released a CPU with the performance of the P200. There was no rush for Intel to release the P200 any earlier, since there weren't any competitors.
Cyrix, IBM and AMD have always been one step behind Intel's latest CPU release and therefore they all have reasons to produce chips which run at the highest possible performance level. They also have to be competitive, resulting in a lower price, which is yet another reason to produce high performance CPUs rather than even cheaper slow ones.
This is, in my eyes, the reason why the official clock speeds of Cyrix, IBM and AMD CPUs are fairly close to their maximum clock speed. All these CPUs run very hot, much hotter than Pentiums. It is tough enough to cool the CPU properly at its original clock speed, much less than at overclocked speed.

Although there are now new and 'cooler' 6x86 and K5 chips on the horizon, I claim the following:

Cyrix, IBM and AMD CPUs are already 'overclocked' at their original clock speeds. The CPU reliability demands of Intel for specifying the original clock speed are much much higher than those of Cyrix, IBM or AMD. Hence, we should even thank Intel for its tough CPU testing procedure because it makes Intel CPUs the easiest chips to overclock available. You already paid a lower price for your AMD, Cyrix, or IBM CPU than you would have for a comparable Pentium, so you shouldn't expect even more performance out of a less expensive chip. This is also the reason why Intel can live quite well with my website - they would still prefer you buy an Intel CPU and overclock it, instead of buying a Cyrix, IBM, or AMD CPU.

It's just like tuning engines, there is still a lot of performance to get out of a big Mercedes or BMW engine, but you can't gain performance by tuning the already maxed out engine of a 750er Ninja (Kawasaki ZX-7R)?