The ultimate guide to overclocking

When it's up to 372MHz, we need a mobo that's happy at nearly 1,500MHz. That simply isn't a given, especially on cheaper boards, so shop carefully. As well as that, if you've got a board with a stingy BIOS, you may not be able to alter RAM and PCI timings independently of the FSB, which can lead to those falling over.

Ours does, and for our mighty near-Gigahertz Q6600 overclock, we have to lower the RAM's clock speed a little to compensate for the strain put on it by the raised FSB - we have it sitting pretty at 893MHz. It could comfortably go higher, but the real-world benefits (as opposed to the willy-waving benefits, which are a different matter entirely) would be so miniscule that it's simply not worth placing the extra pressure on the RAM.

Similarly, while faster and, most likely, more expensive RAM will cope better at their stock speeds with a massive FSB, the pay-off is often so minor that value RAM, running at a lower clock-speed may well be enough to make your overclocking masterplan hugely successful. Even the best memory will net you something in the region of just a five per cent performance boost - worth having if every little helps, but it's the FSB that makes the big difference. And for that, the motherboard is critical.

Thirdly, there's the matter of voltage. The faster your chip runs, the more power it needs to feed it. As the FSB goes up, you'll find your motherboard's North Bridge and your RAM also get hungrier. Unfortunately, your hardware will automatically report its revised power requirements, so trial and miserable error are required to find the sweet spot. Volt tweaking is a fiddly and danger-fraught business.

Some overclocking-friendly motherboards can automatically adjust voltages for you, but are understandably conservative about it, so for the really big overclocks you'll need to set 'em yourself. This needs to be done by the tiniest increments possible, establishing reboot-by-reboot how many volts your embiggened CPU needs; as low as possible, essentially, as firing too many into it can fry it.

Establish in advance what your chip's out-of-the-box volts are and, through a mix of common sense and googling, decide on a number you're not going to risk going higher than. We pushed our Q6600 from 1.3 to 1.4V, which is a fairly big increase as volt modding goes. It's not just a matter of the so-called vCore either - as you go for the big overclocks, you'll find you're having to play with the arcane likes of CPU PLL and FSB termination voltage. Again, so long as you raise stuff in tiny increments the risk of slagging your chip, RAM or mobo is fairly minimal.

Overclocking AMD processors

It's a different matter with AMD processors, which for a while now have had an onboard memory controller, which allows the chip to communicate more directly with the RAM, which in turn means there isn't an FSB as such.

Instead, you're overclocking something known as the HyperTransport bus, which is achieved in more or less the same way, but can require lowering the HT's own multiplier to retain stability when you bump the speed. If you've gone for one of the recent AMD Phenom Black Editions, you'll find it comes with the multiplier unlocked, which makes overclocking an easier affair.

Overclocking graphics cards

By contrast, overclocking a graphics card is dead simple. As a more self- contained piece of hardware, there's none of this confusing multiplier or FSB business; just overclocking the card itself, finding the right speeds for both the GPU and the card's onboard memory.