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A beginner's guide to overclocking

How to get your feet wet with Core 2 overclocking

TR Overclocking Guide - Sponsored by Gigabyte

As a PC enthusiast, my desire to overclock is almost compulsive. Pushing clock speeds must be hard-wired into my DNA, because I can't actually remember the last time my personal workstation ran at stock speeds.

Overclocking isn't for everyone, though; it can be time consuming and frustrating, and it will almost certainly void your warranty. But there's a unique sense of satisfaction to be gained from pushing your hardware to its limits and achieving greater performance than you've actually paid for. For enthusiasts, many of whom have a borderline obsession with deriving the best bang for their buck, overclocking's potential is simply too hard to resist.

To help the uninitiated get their feet wet with overclocking, we've whipped up a handy guide covering the basics. This is by no means an attempt to document every technique associated with turning up your system's clock speeds, but it should be a good place to start for newbies looking for their first taste. We've chosen to focus our examples and advice on Intel's Core 2 processors, since they're a particularly popular choice right now, but many of the basic principles we're exploring apply to any chip you might want to overclock, including AMD CPUs.

What is overclocking?
Simply put, overclocking refers to running a system component at higher clock speeds than are specified by the manufacturer. At first blush, the possibility of overclocking seems counter-intuitive—if a given chip were capable of running at higher speeds, wouldn't the manufacturer sell it as a higher speed grade and reap additional revenue? The answer is a simple one, but it depends on a basic understanding of how chips are fabricated and sorted.

Chip fabrication produces large wafers containing hundreds if not thousands of individual chips. These wafers are sliced to separate individual dies, which are then tested to determine which of the manufacturer's offered speed grades they can reach. Some chips are capable of higher speeds than others, and they're sorted accordingly. This process is referred to as binning.

There's considerably less demand for faster chips than for slower ones, though. The Core 2 Extreme QX9650 may be the fastest CPU Intel can produce, but with street prices hovering around $1200, it costs quite a bit more than most folks are willing to spend on a CPU. The Core 2 Quad Q6600, which sells for less than $300, is in much higher demand because it fits within the budget of a greater number of consumers. And demand for low-end chips is even greater still.

Chipmakers often find themselves in a position where the vast majority of the chips they produce are capable of running at higher clock speeds, since all chips of a particular vintage are produced in the same basic way. So chipmakers end up designating faster chips as lower speed grades in order to satisfy market demand. This practice is of particular interest to overclockers because it results in inexpensive chips with "free" overclocking headroom that's easy to exploit. That's the magic of binning: it's often quite generous. A great many of the CPUs sold these days, especially the low-end and mid-range models, come with some built-in headroom.

Overclocking can do much more than exploit a chip's inherent headroom, though. It's also possible to push chips far beyond speeds offered by even the most expensive retail products. Such overclocking endeavors usually require more extreme measures, such as extravagant cooling solutions, so they're a little beyond the scope of what most folks will want to tackle.

What you need
The most important ingredient in any overclocking endeavor is a good chip. If you're looking to exploit the "free" overclocking headroom made possible by binning, you're best off looking at lower speed grades. If you're after the maximum overclock, you'll probably want to pick the number of cores and the amount of cache that you want, and then select the lowest speed grade available with those characteristics. If you have a choice between chips with different front-side bus speeds, it's probably best to pick the chip with the lower default bus speed. A slower front-side bus can make life easier for the motherboard, and you may even be able to overclock the processor without pushing the board beyond its specifications.

Overclocking forums are also rife with discussions of specific CPU steppings and batch numbers that have higher success rates than others. If you're willing to do a little research—and if you can coax retailers into giving you more detailed information on chips they have in stock—you can increase your chances of success. Gathering stepping and batch information is particularly useful if you intend to push clock speeds well beyond any binning freebies.

Of course, success is never guaranteed with overclocking. Your mileage will amost certainly vary, and you might even end up with a complete dud incapable of running more than a few MHz faster than its stock speed.

Just because we're focused on processor overclocking doesn't mean that other system components aren't important. A system's motherboard, cooling system, power supply, and even memory can affect the success of an overclocking attempt. These don't necessarily need to be expensive high-end parts—that would defeat much of the value proposition behind overclocking—but you'll be better off with quality components from reputable manufacturers.

On the motherboard front, you want to ensure that the BIOS has ample overclocking options, including the ability to manipulate bus speeds and system voltages. The more control we have over system variables, the more freedom we'll have to tweak settings carefully in pursuit of higher clock speeds. Motherboard cooling becomes more important when you turn up clock speeds, as well. You don't need a mess of heatpipes snaking every which way on the board, but try to stay away from boards with tiny chipset coolers that don't offer much surface area to dissipate heat.

Ditch the puny stock heatsink (left) for something beefier (right)

Depending on how far you intend to push clock speeds, you may also want to consider beefing up your system's CPU cooling. Overclocked chips tend to run hotter than those at stock speeds, particularly when you start increasing the CPU voltage, and you don't want a stock cooler holding your system back. Aftermarket coolers designed for overclocking feature significantly more surface area than the stock coolers AMD and Intel bundle with their processors. Aftermarket coolers also tend to have much larger fans to generate more airflow, often while making less noise. Decent coolers can be had for as little as $30, so they won't put a big dent in your budget.

We always recommend that users spend a little extra to get a quality power supply for their systems, and this goes double if you want to overclock. Our concern here isn't getting gobs of extra wattage, but ensuring that the PSU delivers clean power to the system.

Fancy memory isn't always necessary if you're looking to overclock a processor, but DIMMs rated for operation at higher frequencies can give you a little more freedom when playing with clock speeds. Memory module manufacturers often guarantee their products to run at higher clock frequencies, even if those speeds aren't officially endorsed by the JEDEC standards body that governs system memory.

Even more important than individual component choices is having a completely stable system before you dive into overclocking. If you're building a new system from scratch, stress test it at stock speeds to ensure that everything is working properly. The last thing you want is to burn an afternoon trying in vain to overclock a system hampered by a faulty component that isn't even stable at stock speeds.

The obligatory warning
Overclocking will probably void your warranty, and it has the potential to damage not only the hardware being overclocked, but other system components, as well. This is where The Tech Report absolves itself of any responsibility for damaged hardware, voided warranties, puffs of magic smoke, core meltdowns, and bruised egos that may result from unsuccessful overclocking attempts. Or, heck, even successful ones.

We should also warn you that this guide covers overclocking through the motherboard BIOS. If you're not comfortable poking around in the BIOS, you probably shouldn't be overclocking in the first place.

Finally, before you begin overclocking your CPU, you should start by making a backup of any important data on your system. You may even want to consider using a disk imaging program like Symantec Ghost to make a complete image of your boot partition. We've seen more than one OS installation rendered unbootable by file corruption caused by an unstable processor in the midst of an overclocking attempt. The trial-and-error process of seeking a stable overclocked configuration necessarily involves some risk on this front, so make provisions ahead of time.