Sometimes getting the best bang for your buck with PC components means putting a little extra work in, whether that's shopping around for the best prices online, or researching which CPU or GPU is best suited to the task at hand. But, if you're willing to go the extra mile, the best returns often come from overclocking. For the uninitiated, overclocking means taking a piece of hardware--most commonly a CPU or GPU--and running it at a faster speed than the manufacturer intended, giving you the performance of higher-priced models for less cash. While there's an element of risk to the process--you can significantly shorten the life of your components or permanently damage them if something goes awry--if you're sensible, disasters are rare. The process of overclocking isn't as complicated as some would have you believe either, and with a bit of computing know-how, and some patience, it's possible to significantly boost your PC's performance with just a few tweaks.
Before you begin overclocking, it's good to know some of the basic principles behind the process, beginning with how a CPU's speed is calculated. While the overall speed of a CPU is based on a number of factors, one of the most important is its clock speed, which tells you how quickly the CPU switches from one cycle of instructions to the next, and is measured in gigahertz (GHz). For example, Intel's new Core i5-4690K has a standard clock speed of 3.5GHz, while AMD's FX 9590 Black Edition has a standard clock speed of 4.7GHz. Both processors also feature a turbo mode, which dynamically increases the clock speed in small bursts, as well as power-saving features that decrease the clock speed when the CPU is idling.
What we're most interested in when overclocking is the standard clock speed. You calculate it by taking the base clock (BCLK, a signal supplied by the clock generator on the motherboard, or reference clock in AMD systems) and applying a multiplier to it. For example, the Intel Core i5-4690K is designed for motherboards that feature a base clock of 100MHz, while the CPU itself has a default multiplier of 35. All you do is take that multiplier of 35 and multiply it by the 100MHz of the base clock, which equals 3500MHz, or 3.5GHz. Therefore, to make the processor run at a higher speed, we need to increase either the base clock or the multiplier. Increasing the BCLK used to be common practice in the old days of overclocking, but these days, adjustments are limited to just a few MHz, and only with specific motherboards.
The preferred method whether you're using an Intel or an AMD CPU is to increase the multiplier until a stable speed is reached. However, this increase in speed causes the CPU to suck down more power, and if not properly accounted for, this can cause system instability. The solution is to manually adjust the CPU core voltage (VCORE) while still keeping the system stable. Bear in mind, though, that there's a cutoff point where too much VCORE actually introduces instability and can damage or shorten the useful life of your CPU. Plus, with more VCORE comes more heat, which brings us neatly to what exactly you need in your system before you start overclocking.
Get the Right Gear
Thanks to the extra heat put out by overclocking, you need to make sure you've got adequate cooling in place before attempting it. While you can achieve small overclocks using stock cooling solutions supplied by the CPU manufacturer, it's far better to go with a large third-party cooling solution from the likes of Noctua or Corsair. The more efficiently you can move heat away from your CPU, the more stable your overclock will be. It's also worth looking at the overall cooling setup in your PC, and making sure that you have decent fans and good airflow throughout the case. For more on keeping your PC cool (and quiet), be sure to check out our guide.
Aside from decent cooling, you also need to make sure you have the right type of CPU and motherboard. Not all CPUs support multiplier overclocking; the vast majority have their multipliers locked. On the Intel side, look out for CPUs with a "K" in the product name, such as the Intel Core i5-4690K. On the AMD side, you need a Black Edition chip, such as the AMD FX-8350 Black Edition. Older CPUs from older product lines may differ, so do your research before proceeding. You can read more about CPUs in our extensive guide. And if you're planning to overclock your GPU, we've got a guide on what to look out for there too.
To go alongside your overclockable CPU, you need a motherboard that supports overclocking. On the Intel side, that's any motherboard with a "Z" designation, such as the Z77, the Z87, or the more recent Z97, depending on what CPU socket you have. Things are a little easier over on the AMD side in that most motherboards support overclocking of some sort. However, bear in mind that overclocking increases the amount of power flowing through the motherboard to the CPU. That power is delivered by a section of a motherboard called the voltage regulator module (VRM). Cheaper boards don't have particularly hardy VRMs, which makes them bad for overclocking. Essentially, you want a VRM with good-quality leak-resistant capacitors, high-quality chokes (used to improve efficiency, often called super ferrite chokes), and a decent cooling solution in the form of a heatsink or even a fan over the MOSFETS.
Finally, if you're driving extra VCORE to the CPU, your PC is going to use more power. That's particularly true for AMD CPUs, which already have a thermal design power as high as 225W at stock speeds. That means your power supply unit (PSU) has to be up to the task. We're going to be taking a more in-depth look at PSUs at a later date, but the PSU is one thing you don't want to skimp on. Look for 80-plus-rated units and research what sort of power output, rails, and efficiency you need. Also, be sure to pick up a PSU from a reputable manufacturer like Corsair or Silverstone. The last thing you want is to fry all your expensive components because of a cheap PSU!
Preparing Your System for Overclocking
There are three main methods for overclocking your CPU via the multiplier: using the automatic overclocking tools of your motherboard, manually overclocking using software in your operating system, or manually overclocking using your motherboard's BIOS or UEFI BIOS (a page of system settings you access when you boot up your PC). It's the latter two we're going to be focusing on here. Automatic overclocking tools can work brilliantly sometimes, depending on the motherboard manufacturer, but they don't always result in the best performance gains. If you're totally new to the process and don't want to dive in too deep, automatic overclocking tools are a good place to start. Just check out your motherboard's manual and see what it offers.
The process for manually overclocking by using software tools (often provided by the CPU or motherboard manufacturer) or by diving into the BIOS is very similar, but it's generally better to overclock using the BIOS if you can. In software, the settings are loaded only when your OS boots, and you can get better, more stable performance gains using the BIOS. The exception to this is GPU overclocking, which can be achieved only via software. For the purposes of this guide, we're going to focus on BIOS overclocking, but you can apply many of the same principles to software tools.
Before you begin your overclocking journey, make sure that you've backed up any important data and that you're running the latest version of your motherboard's BIOS. You'll also need to install a few bits of software in your OS to test the overclock and system stability, and get some baseline figures for comparison, all of which are free. First, grab a copy of CPU-Z. This tool gives you all sorts of real-time system information, but here you'll be using it to keep an eye on the clock speed of your processor and how much voltage is being applied to it. Next, download Prime95, Cinebench, and PassMark BurnInTest. These tools are used to ramp up your processor usage to test system stability.
Finally, install Real Temp. As its name suggests, Real Temp lets you monitor your CPU temperature, so you can check that it's not straying over 75 degrees centigrade when the CPU is under full load, with 60 being much more comfortable. Once you've got everything installed, run a "blend test" in Prime95 and note down the core voltage figure with your system under load. Also check the CPU temperatures in Real Temp. Do the same again, except this time with the system idle. You'll notice that your CPU speed and voltage drop significantly when the CPU is not in use, which is a handy power-saving feature, and one that we'll show you how to still make use of when overclocking.
How to Overclock
Boot into your motherboard BIOS at startup (how you do this varies, but it's usually accomplished by pressing the delete or F8 key), load up the optimised default settings (again, usually accomplished by a key press), and then reboot and enter the BIOS again. Open up the advanced settings and find the page that contains setting for your CPU and/or memory. You should see things like "BCLK Frequency" or "CPU Voltage" in there. Sometimes these settings are hidden away, so consult your motherboard manual for how to unlock them. In the case of our ASUS motherboard, we had to set "Ai Overclock Tuner" to "Manual" and then "EPU Power Saving Mode" to "Disabled" to see the full gamut of options.
While a significant overclock usually means applying more VCORE to the CPU, for now you need to find out how far you can push your CPU without adding any voltage. Find the setting for your multiplier (called CPU core ratio on ASUS motherboards) and change it from "Auto" to "Sync Across All Cores." Some motherboards feature a "Per Core" option, which allows you to change the speed of each CPU core individually. It's a useful way to get a higher overclock on individual cores, but for simplicity's sake, go ahead and select "Sync Across All Cores" or a "Manual" option. To start with, increase the multiplier number by 1. So, for the Core i5-4690K mentioned earlier, the default multiplier is 35, giving us a speed of 3.5GHz. With an addition of 1 to the multiplier, we hit a speed of 3.6GHz.
Save your BIOS settings, and boot into Windows. We'll be doing much longer stability tests later, but for now, run a few passes in Cinebench to check that things are relatively stable, and keep Real Temp open to make sure things aren't getting too toasty. Repeat this process until your PC no longer boots, or your PC blue screens. If your PC no longer boots, you'll need to reset your BIOS. Many motherboards now have a button on them that lets you do this with little effort, but some older boards may require you to move a jumper on the physical board. Consult your motherboard manual for how to do it.
Once you've encountered an error, back the multiplier down to the last stable point. Now it's time to start fiddling with the VCORE. Find the setting for "CPU Voltage" or similar in your BIOS, and set this to "Manual" for now. This is the setting for a fixed voltage, meaning that regardless of whether your CPU is under load or idle, it will receive the same amount of voltage from the motherboard. You'll notice that you're also given the option of "Offset" or, if you're using an Intel Haswell CPU, "Adaptive." What these do is work in conjunction with the power-saving features of your processor to step the voltage down when the CPU is under a light load or is idle. We'll look at enabling these later in the article.
There are two options from here. The more involved method is to begin to increase your VCORE in gradual steps. Remember that VCORE figure you noted down when the CPU was under load at stock speed? Take that figure (you might also find the figure listed in your BIOS) and add 0.5v to it. Save and reboot and then begin to increase your CPU multiplier again. Increase the multiplier--testing it out each time with Cinebench and monitoring your temperatures with Real Temp--until you hit another blue screen or failed boot. Make sure you're noting down the figures each time in case you need to do a BIOS reset to boot your system. Add another 0.5v to the VCORE and start increasing the multiplier again. Repeat the process until you reach your desired overclock, your temperature gets too high under load, or you're putting more than 1.4v into the CPU.
Higher voltages are possible, but you risk shortening the life of your CPU, and they certainly aren't recommended if you're running an air-cooling setup. Most recent Intel Haswell CPUs will hit 4.5GHz at around 1.2v, although AMD systems will need a little more juice. The alternative method, which is especially useful for more modern CPUs, is to jump straight in at 1.2v and go about increasing the multiplier from there, which speeds up the process a little. Either way, once you find a point where the system is mostly stable, you need to run some more substantial tests to make sure it's not going to crash under extended loads.
There are various opinions around the best method for stress-testing your PC. One of the most popular is running Prime95's blend test over a 24-hour period. If your PC manages it without any error messages in Prime95 or without crashing, your overclock is stable. However, Prime95 is what's known as a synthetic benchmark, in that it doesn't entirely reflect real work usage. For that, things like Cinebench and PassMark BurnInTest provide a much more realistic type of CPU load. Either way, if your PC crashes or fails a test at any point, either increase your voltage again in smaller 0.01 steps or decrease your CPU multiplier, keeping an eye on temperatures the whole time. Eventually, you'll find the sweet spot for your CPU.
Success: you've overclocked your CPU! From there you can go ahead and enable X.M.P. profiles for your RAM, or manually input its speed (in MHz) and timings (listed on the RAM itself in a 9-9-9-24 format) to make sure everything is running at its correct speed. You can also enable "Adaptive" mode on your motherboard, so your CPU's voltage is stepped down when it's under less load. You'll find two extra settings to fill in with Adaptive mode: Idle VCORE and Turbo VCORE. Essentially, all you do is input a +value into Turbo VCORE that adds up to your desired overclocked voltage. So, for example, if your stock VCORE is 1.10v and your stable overclock is at 1.25v, input +0.15. You may find that under Adaptive mode, your CPU becomes unstable at idle speeds, because it's not getting enough voltage. In that case, input a +value into Idle VCORE to account for it.
Be aware that when using Adaptive mode, synthetic benchmarks like Prime95 that use certain advanced vector extensions (AVX) can cause the motherboard to deliver a higher voltage than necessary. This shouldn't affect you unless you're doing a lot of scientific floating-point calculations, but if that's your bag, a fixed voltage is best. If your motherboard doesn't offer Adaptive mode, you can use Offset mode. There's a lot more trial and error involved in setting up Offset mode, but the principal is the same. Essentially, the CPU has a voltage it thinks it needs in order to run at a given speed, called the VID. That may or may not be the actual voltage it needs, so all offset does is to add (or subtract) a set amount from the VID to get the correct voltage.
The good news is that all the principles of CPU overclocking also apply to GPU overclocking. Both AMD and Nvidia actually include overclocking support as part of their drivers. AMD's are in the Performance section of Catalyst Control Center, while Nvidia's are unlocked by installing its System Tools utility. The process is as simple as adjusting the sliders for memory speed, clock speed, and fan speed and testing the results in your favourite game. The beauty of the built-in overclocking tools is that they don't adjust voltage, so you can pretty much go crazy with the sliders and find an overclock that works well for your GPU. If you want to go further, tools like MSI's Afterburner let you tweak voltages, but aren't recommended unless you've got a hefty cooling solution in place.
Tempted to overclock your PC? Already an advanced overclocker? Let us know your overclocking stories in the comments below.