For those more advanced users that already know how to overclock and don't want to listen to me explain this process then you might want to skip ahead to the next page.
Ok for those that are new to the overclocking scene, the basic theory behind it is that CPU's are over engineered and often can run at speeds higher than what the manufacturer says they can.
So what is the appeal of overclocking? Well one, to saving money. Why pay some of the ridiculously high prices for gigahertz processors when you can pay 1/2 to 1/4 less and overclock your chip to a gigahertz? Another reason why people overclock is simply to have the fastest computer available. They want to crank that extra FPS in games, or that want to get that extra ray trace out of their equipment. Or simply just to say I'm faster :p.
So what is the goal of most overclockers? To go as fast as you can with hindering everyday usage or effecting the systems stability. Basically we want our computers to go as fast as possible but we don't want them crashing all of the time.
How exactly does overclocking work? Overclocking for all practical purposes relies on the manipulation of the system bus or front side bus (FSB) to produce higher CPU frequencies. Your CPU gets its speed by taking the system bus and multiplying it by a multiplier that is locked in the CPU. So a PIII 550 has a FSB of 100 Mhz and a multiplier of 5.5. Multipliers only come in half or whole numbers (2, 2.5, 3, 3.5, 4, 4.5, ect.) and are locked in the CPU by the manufacturer.
So if you want to overclock a PIII 550 you would set your system bus to something higher than 100 Mhz, so lets we want to overclock this P3 550 to 632, we would raise the system bus to 115 Mhz (5.5 * 115 = 632). Thus increasing the speed of the CPU by 15%. What is the draw back to this method of overclocking? Well you PCI bus, and your AGP bus also derive their speeds from the system bus. The stock speeds for the AGP and PCI bus are 66, and 33 Mhz respectively. Now these speeds are achieved by bus dividers, which are set in the bios or dipswitches. Depending on which motherboard you have, you will have more or less dividers. For my example I'm going to be using a good ole Abit BE6-2 motherboard, which has two dividers for the AGP 1/1, and 2/3; and has 3 dividers for the PCI bus 1/2, 1/3,and 1/4. Which means when I overclock the P3 550 to 632, I increase the PCI bus from 33 to 38. Now PCI devices don't like to be overclocked they like the standard 33 Mhz and unlike overclocking your CPU, you don't get any extra performance overclocking your PCI bus. So it's generally a good idea to try and stay with a normal PCI bus or as close to it as possible. This also means that the AGP bus speed will be increased from 66 to 76 Mhz. Now AGP devices are a little more lenient on the bus speed and seem to still function normally at higher than standard bus speeds, but there are no visible performance benefits of overclocking you AGP bus at all, so the closer you can run it at the default bus the better. Another problem with overclocking by raising the FSB especially with the newer 133 Mhz chips is that your ram will quickly crap out on you… This is because on most motherboards the speed of the ram is the same as the system bus. So you quickly run out of speeds that you can overclock to due to the limitations of your ram.
Stability should be the goal of all overclockers if it isn't stable your speed isn't valid. How do we go about establishing if your CPU is stable are not? Well there are a bunch of tests that we run to establish if your CPU is stable or not. The first test that we need to run is the Prime95 self-test. This test stresses you CPU and level 2 cache by calculating prime numbers then checking the results. This test will last for 16 hours and if your CPU passes with out generating an error then your CPU can be considered about 95% stable. So why does this test determine so much of your stability? Well the hardest thing for your CPU to do is to calculate and store prime numbers. So by running this test on your system you put it on the most stress full load that your CPU will probably ever experience. Now just because your CPU passed the Prime95 self test, doesn't mean that your system is stable. You now need to stress your entire system to see if it cracks. And what better way to do that then games! But not just any games, you won't test system stability by playing 99 games of solitaire. I'm talking about intensive 3d games like Quake3, Unreal Tournament, or Half-Life. So what if you don't own these types of games? Well lucky for you there are demo's that you can download and run. Now you can play with your new toy as long as you like but I would recommend that you at least run them for 3 or more continuous hours to thoroughly test your system. If you make it past the 3+ hours with out crashing congratulations you have successfully overclocked your CPU, and can either stay with your current speed or you can try for a higher speed.
But what if your computer failed the stability test, failed to post, or booted into a black screen when your windows desktop should of popped up? Well there are a couple things that you should do. First, check to see that your not trying to overclock to some ridiculous level like trying to make a Celeron run at 133+ Mhz a peltier helps but it doesn't work miracles. Usually a 20-30% bus increase is a respectable level for overclocking and a realistic goal for most coppermine processors. Next, check that you PCI and AGP dividers are set so that you get close to default speed as possible, if need be its better to have your buses run faster than slower. Next, check your core voltage, if you increased your bus speed let say 10+% and it wasn't stable increase your core voltage .05v, until your chip is stable, please note not to go past the specified max voltage. Also if you overclock more than 20% your going have to change you voltage more than the .05 volts over default, a good voltage to try when you overclock 20-30% is around 1.7v to 1.75v for coppermine CPU's. Next if your overclocking towards the extreme side 25-30% and you can't get your chip to be stable at all and your running at the max specified core voltage, then you have to live with the reality that you chip simply just isn't stable at that speed and must settle for a lower one. You have to realize that part of overclocking is simply luck. And you must also realize that all chips are not created equal some will overclock really high, some don't overclock at all, it all depends on your chip. So just because you saw someone hit a really high speed doesn't mean that your chip can, but you never know.
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