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Posted: January 25, 2000
Written by: Keith "Farrel" McClellan
There are a couple of very important things to keep in mind when you are attempting to overclock a computer, so that you don't damage your equipment. The first of these things is to make sure you have adequate cooling to take on the project you are planning. As will be discussed later, cooling can make or break an overclock - but that isn't its only benefit. It also helps prevent damage being done to the chips due to excessive heat.
Ok, now that I have taken care of explaining the importance of cooling to you, on to the (second) most important safety precaution - which has to do with progressive overclocking. I know, I know, that isn't a term most people have ever heard of - and that's because I just coined the term. Progressive overclocking has to do with the process of slowly clocking your system faster and faster until it reaches its peak stable speed. This is frequently done with video card overclocks, because it is very easy to over do it and fry the card. The process with video cards is very easy - you simply overclock in 5 MHz increments until you reach an unstable speed, and then downclock the card in 1 MHz increments until you reach a stable speed. Then of course comes the obligatory testing to determine whether or not the card is stable even during system strain - and if it passes, you're gold.
However, the process with a CPU is more difficult - mainly because it is hastlesome to go back into the BIOS for every clock change. With bus clocks, bus multipliers, and chip voltages to contend with, things aren't always hunky-dory.
Bus Clock Speeds
The system bus clock is a very important concept when dealing with system overclocking, particularly when you are dealing with an Intel-based system. This is because Intel's processors are multiplier locked. More on that subject later, however. Right now I want to explain to you about the system bus and how it can effect your system.
The bus clock I am referring to is the system bus on which the processor communicates with the rest of the computer. It is derived directly from the computer's internal quartz crystal which runs at ~12 MHz (and subsequently also runs the computer's internal clock). This bus speed, when taken into account with the processor's bus multiplier, determines what speed the CPU runs at, as well as some other things. You see, the PCI and AGP slots derive their bus speeds from the system clock (33 and 66 MHz respectively) using a bus divider. These dividers have been set up specifically for the standard system bus speeds (66/100/133), but don't work quite as well for the non-standard bus speeds. That means that, unless you are jumping from 66 to 100 MHz, or from 100 to 133 MHz, you will also have to over or under clock your system buses - and sometimes they don't take kindly to the extra stress.