Overclock your PC

Increase the performance of your CPU—for free! We tell you everything you need to know to do it safely and effectively

If you’re running your CPU at stock speeds, you’re missing out on your PC’s true potential, because processors often harbor power beyond their official specs. Your proc, for example, might be rated to run at 3GHz but is actually capable of operating reliably at 3.3GHz. There are myriad reasons for the hidden headroom, ranging from natural variance among parts (even those made from the same batch), to the manufacturers’ practice of underclocking parts to meet market needs, to the improved capabilities of a part over the lifetime of its production.

The point is, you’re not a true power user if you leave a CPU’s hidden performance potential untapped. And the only way to release your proc’s inner speed demon is to overclock it. This story will tell you how. Even if you’ve dabbled in the practice in the past, you’ll want to read on. Because just as CPUs have changed over the years, so has the art of pushing them to their limits. Over the following pages we’ll tell you everything you need to know about overclocking today’s CPUs, be they AMD- or Intel-branded. We’ll explain what’s involved, how to determine what your hardware is capable of, and how to achieve optimal results. Most importantly, we’ll tell you how to overclock safely. Indeed, overclocking is serious business and should never be taken lightly.

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!

The Basics of CPU overclocking

Pushing your processor to new heights can be extremely rewarding—if all goes right. Take the time to understand the concepts of overclocking and the factors that can affect succes

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 front-side 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 fixes 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! 

Have the Right Hardware

Your CPU isn’t the only part that matters in your quest for more speed. Here are the other components to care about

Motherboard

You get what you pay for and, generally, a cheap-ass motherboard will yield marginal overclocking results. The more expensive the motherboard, the more likely it is to have better components and better overclocking capabilities. That doesn’t mean all sub-$100 mobos are overclocking duds, but you’ll have to troll the forums and customer reviews on enthusiast sites to determine if a cheapo mobo can OC.

One additional tip: If you’re buying a motherboard for overclocking, you’ll likely have the best success with the latest “spin.” Mobo vendors update their boards with fixes and more recently built boards will usually overclock better.

Power Supply

We’ve long said that the PSU doesn’t get the attention it’s due, and that’s especially true when it comes to overclocking. The fact is, the need for clean, reliable power is of utmost importance if you’re pushing a CPU, RAM, and motherboard to the edge.
If you have a high-compression engine in your street racer, are you going to fill it with 85 octane fuel? A cheap power supply is the equivalent of questionable Kwik-E-Mart gasoline. For overclocking, you don’t need a 1,200-watt PSU, but you do need a name-brand unit. Generally, it’s safer to have a PSU that delivers a bit more power than you need. While it may not be the most power-efficient scenario, a 750-watt PSU running at 450 watts will probably live longer than a 500-watt PSU running at 450 watts.

Cooling

Excessive heat can cause system instability, so it’s essential to keep your overclocked CPU cool. To achieve extremely high overclocks, some hobbyists bathe their CPUs in liquid nitrogen. Others use phase-change units (essentially tiny freezers) to push 3GHz chips past the 5GHz mark. The point is, you can’t expect to push your 1.86GHz proc to a reliable 4GHz using a $12 heatsink. Know your overclocking goals and then choose your cooling accordingly. Air cooling is the most modest solution, followed by water cooling, peltier/liquid combinations, phase change, and exotic liquids, such as liquid nitrogen. Also remember that the extra heat produced by overclocking will warm up the rest of your machine, so you may have to upgrade your case’s cooling or the case itself if you experience overheating issues. For our CPU cooling recommendations, see page 34.

Memory

In the old days the front-side bus’s speed was tied to the speed of the system RAM, so you had to overclock both. That’s no longer the case, but some folks still prefer to give their RAM some extra juice. This is the purpose of pricey, high-performance RAM. It’s been certified by the RAM manufacturer to operate at a given “overclocked” speed. We say overclocked because RAM speeds and timings are actually spec’d by an organization called JEDEC. The top standard speed of DDR2 today is 800MHz. Overclockable DDR2 RAM generally runs in the 1,066MHz range, with some pricier modules pushing 1,250MHz. While it’s not necessary to overclock your RAM to overclock your CPU, there are some instances when you will get improved performance if the FSB and RAM run at similar speeds that are closely synced. Some applications will also favor the increased bandwidth of overclocked RAM. Your research will help you determine if this applies to your parts.