Overclocking your processor can give your PC a significant speed boost - but you have to be careful. Here's how to overclock your system's processor without frying it.
We'll be looking at three different CPUs, each on a different motherboard. The first combination is AMD's latest high-end CPU, the Phenom II X6 1090T running on an Asus Crosshair IV motherboard (the high end of the Asus line for AMD processors, typically priced at around £150 to £200).
The second pairing is Intel's new Core i7 875K clock-unlocked CPU - the high end of Intel's socket 1156 processors - running on an Asus P7P55D-E Pro, which costs about £125. The Core i7 875K is easy to overclock and can push to extreme clock frequencies quite easily.
The last processor/motherboard combo is Intel's Core i5 750 - a modestly priced, clock-locked processor that nevertheless has substantial overclocking possibilities - running on a Gigabyte GA-P55M-UD4 micro ATX board, which is available for around £110.
Automatic, semiautomatic or manual?
Many motherboards today offer automatic (or semiautomatic) overclocking. We tend to avoid the fully automatic overclocking. When it is enabled, the BIOS setup program runs a few tests and then sets the various clock speeds (CPU and memory) to the highest clock speeds it considers stable. We've found, however, that these high speeds often become unstable when you boot into Windows and try to run applications for a significant length of time.
The semiautomatic approach lets you pick from several overclocking presets and specify limited overclocking. Asus' 'CPU Level Up' feature is one example of this approach.
Let's walk through a semiautomatic scenario using Intel's unlocked Core i7 875K processor. First, press the Delete key during the boot process to get into the BIOS setup program. One of the tabs in the Asus setup is Ai Tweaker, which is a one-stop shop for tweaking system settings. Navigate through the screen with the arrow keys, and press Enter to select a particular setting to change.
The first setting you can change is 'CPU Level UP'. The setting options are Auto (which doesn't do much) and three presets, each prefaced by the word 'Crazy'. As it turns out, the first two settings aren't all that crazy; they simply let you boost the clock rate by one or two speed grades.
For the CPU Level Up feature to work with this particular CPU, open the Advanced tab, select Intel SpeedStep Technology (you'll have to scroll down the screen to reach it) and disable it. Note that disabling SpeedStep also disables power management. You didn't think that overclocking would be free, did you?
After you select one of the first two 'Crazy' options in CPU Level Up, the system will boot up and run at the higher clock speed.
Using CPU Level Up carries some risks. For example, though we're using an unlocked CPU, the BIOS setup assumes that the multiplier is locked. So instead of increasing the clock multiplier, the CPU level up boosts BCLK to 160MHz at the 'Crazy-3.52G' setting - and that alters memory timings.
Though our particular CPU was stable at 3.52GHz under stress testing, we recommend sticking with the 3.2GHz setting. That's almost certain to yield a successful overclock with this CPU, and it pushes BCLK to a less aggressive 146MHz. The memory speed isn't much greater than the default 1066MHz, but it is a little faster, at 1170MHz.
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