Overclocking basics

Back in ancient times (1990), a computer's CPU frequency was essentially the entire computer's frequency. A computer running at 5MHz, or 30MHz, meant that just about every single component in the computer ran at that speed too. As processor technology improved, engineers realized that running the CPU at the same speed as the system might not be the best way to go about things. At that point, starting with Intel's 486 class of CPUs, multipliers were born. The Intel 486DX2 66MHz CPU ran at twice the speed of the front-side bus (33Mhz) and therefore had a multiplier setting of two. The CPU now ran twice as fast as everything else in the computer. Fast forward to modern day and it's common to see both AMD and Intel use multiplier settings of 15 and above.

The other component to the CPU's final speed is the front-side bus (FSB). The FSB refers to how fast the communication link between the CPU and chipset operates. Modern computers typically operate on a 133MHz, 200MHz, or 266MHz FSB. Although, you've probably seen numbers like 533MHz, 800MHz, 1000MHz, and 1066MHz thrown around, those figures are based off the original FSB. In Intel's case, the company uses a quad-pumped bus that allows the chipset to communicate four times per cycle (or Hz), which means that a quad-pumped 200MHz FSB effectively communicates like it's at 800MHz (4x200MHz). In AMD's case, the company actually stepped away from traditional FSB architecture, and adopted the HyperTransport bus, which has a default value of 200MHz. Using that figure, you then multiply the HyperTransport bus speed and the multiplier to arrive at the final CPU speed.

If you know how to multiply, then you can overclock. Most overclocking follows the following formula:

(Multiplier) x (FSB) = Final CPU speed

Depending on what kind of CPU you own, there are essentially two different methods to overclocking--multiplier overclocking and bus-speed overclocking.

How to overclock using the multiplier

Most people don't fall into this category because the powers that be (AMD and Intel) lock the multiplier on their processors. The only way you can get a factory-unlocked processor these days is to pay exorbitant amounts for AMD's FX and Intel's Extreme Edition line of CPUs.

Multiplier-unlocked CPUs allow you to change the multiplier at will. You can easily switch the 2.6GHz Athlon FX-60's default multiplier from 13 to 14, and have the CPU running at 2.8GHz in no time at all. The great benefit of a CPU with an unlocked multiplier means that you don't have to push the rest of your computer beyond its limits if you don't want to. You can put all the stress only on the CPU and leave the FSB untouched to keep the rest of the system operating within normal parameters.

Most overclocker-friendly motherboards will offer the option to change multiplier settings in the CPU section of the BIOS. However, most of us won't have the luxury of using the multiplier to overclock.

How to overclock using the FSB

If you can't adjust the CPU multiplier, the only way to increase the speed will be to jack up the FSB. When you overclock using the FSB, you're going to stress the CPU as well as just about every other component in the system, which mainly means that you'll need a quality motherboard. If you also want to overclock the memory subsystem, make sure to get premium RAM.

The trick to overclocking the FSB is to move up in small increments until you experience minor instabilities. Motherboards built for overclocking will allow you to edge up the speed in very small increments, and they'll also offer several voltage options to help maintain system stability.

Both types of overclocking can benefit from increased power levels. However, don't push the CPU voltage levels too high. More power inevitably leads to more heat, which directly translates to a reduced electronic life span. If you're trying to squeak out an extra 100MHz with a disproportionate amount of power, you're better off going with the slower speed and a lower voltage setting. You're not likely to notice the difference between 2.8GHz and 2.9GHz, but you will notice when your computer becomes a premature doorstop.

Testing and maintenance

Be sure to thoroughly test your system out before you call it a day. Run tests like 3DMark06 and Prime95 to ensure that your system runs properly. Don't be satisfied with minor, one-off testing either. Run your tests in continuous loops for at least a few hours, if not an entire day. A little testing upfront can uncover major system instabilities early on.

Forcing computer components to operate outside of normal specifications comes with risks. Be well aware that overclocking will void any warranty you have. If you play it safe and only increase the CPU voltage by a few percentage points, the overclock shouldn't affect the longevity of your equipment by very much. As long as you keep the temperatures low, everything should be fine.

An overclocked system using a normal fan and heat-sink cooling unit doesn't require much more care than a non-overclocked system. Get a can of compressed air and clean dust out of the case regularly. Go in for a deeper cleaning if the system starts to lock up while running games or other processor-intensive applications. Clear out the case air filters, and make sure to wipe down the CPU heatsink as well as the motherboard northbridge heatsink to get rid of dust that can trap heat.

Are you an experienced veteran with several processors under your belt? What CPU do you have and how high have you overclocked it?