# The 2008 PC Builder's Bible

When you tamper with the internal workings of your computer’s parts, you do so at your own risk. Overclocking can damage, or even destroy, your CPU, motherboard, RAM, or other system components, and it can void the warranty on those parts. So consider yourself warned about the potential hazards! That said, you’re unlikely to harm your hardware if you overclock with extreme caution and care. And following the advice and instructions we lay out here will help you. So let’s get started!

Determining a CPU’s Speed

There’s simple math that determines the clock speed of any CPU. Each CPU has a fixed internal number called the clock multiplier. That number multiplied by the reference clock of the frontside bus determines the stated clock speed of the processor. For example, an Intel 2.66GHz

Core 2 Quad Q6700 has a clock multiplier of 10. The stock system bus speed for this processor is 1,066MHz. But wait, 1,066MHz multiplied by 10 equals 10GHz. What gives? Intel’s front-side bus is quad-pumped, so its actual reference clock is 266MHz (1,066MHz divided by four). That makes the clock speed of a Core 2 Quad Q6700 10 times 266MHz for 2,660MHz, or 2.66GHz.

This same math applies to AMD’s Athlon 64 CPUs, although, technically, they have no front-side bus; instead, a HyperTransport link connects the CPU to the chipset. A 2.6GHz Athlon 64 X2 5000+, for example, operates on a 13x multiplier using a 200MHz link—the actual HyperTransport link connection runs at 1GHz, as it operates on a 5x multiplier.

You can overclock both Intel and AMD CPUs by increasing the multiplier setting, increasing the “front-side bus,” or both. By using a combination of a multiplier and FSB overclock, you may achieve higher speeds with more stability. Depending on your situation, a combination of both may give you the best overclock, as your motherboard may simply not be up to running at excessively high speeds.

Multiplier Locking

CPU manufacturers will take measures to ensure that a processor runs at its intended speed by locking the multiplier. This fi xes the multiplier setting, so it cannot be changed in the BIOS. This is done primarily to keep CPU “re-markers” from selling cheaper parts as more expensive ones, but it also serves to thwart overclockers.

But not every chip is locked. Intel’s Extreme series of CPUs does not feature multiplier locking nor does AMD’s FX series or some of its new Black Edition CPUs. This gives overclockers who pay the extra price of admission more flexibility in their adventures. A 2.66GHz Core 2 Extreme QX6600 CPU, for example, can be overclocked to 2.93GHz simply by increasing the multiplier from 10 to 11 without having to resort to front-side bus overclocking.
The Role of Core Voltage

When you overclock, you essentially run the CPU out of spec. Upping a CPU’s core voltage allows you to run a CPU way out of spec by further increasing your overclocking headroom. For example, a stock Intel Core 2 Duo E6600 running at 2.4GHz eats about 1.2 volts. To get the same CPU up past 5.6GHz, one overclocker increased the core voltage to 1.9 volts. As you can imagine, if AMD and Intel designed a CPU to operate at a certain voltage, running it higher will greatly decrease the life expectancy of the CPU. This is the most dangerous element of overclocking. The worst we’ve personally seen from overclocking a CPU via its multiplier or front-side bus is instability or a corrupted OS. But by adding a ton of voltage to a processor, you risk nuking it. Proceed with caution!

How Do I Know if My CPU Is Overclockable?

As a rule of thumb, a very mature CPU production line will yield parts that are capable of running at much higher than rated speeds. So, while it’s not a guarantee, overclockers are generally better off with later-stepped CPUs.

An even better way to determine your processor’s overclocking credentials is to download CPU-Z (www.cpuid.com). This freeware utility will identify your Intel or AMD CPU and tell you such nitty-gritty details as the stepping and revision of the proc. Steppings and revisions are internal labels that Intel and AMD use to denote versions. A step denotes larger changes while a revision indicates fairly minor tweaks.

Once you find out that your retail 2.4GHz Core 2 Quad Q6600 is a revision G0 you can rejoice in knowing that it runs cooler and can withstand more heat than the previous B3 step version. You learn those particular CPU qualities only by doing research, and the best resources are online overclocking databases. Almost every enthusiast PC site has a section devoted to overclocking, where users post details of their own experiences with various CPUs. MaximumPC.com, ExtremeSystems.org, and FiringSquad.com all include areas for users to discuss overclocking exploits.