CPU Buying Guide


Overclocking

Overclocking is a popular pastime for PC enthusiasts, and involves squeezing additional performance out of a CPU by altering the frequency at which it is run. Clock speed is a combination of the Front Side Bus speed of the motherboard and the clock multiplier of the CPU. By altering either the FSB or clock multiplier, you can, in theory, up the overall frequency of a given processor. To do this, you need overclocking to be supported on both the processor and the motherboard.

The most common way to stop users overclocking is to lock the clock multiplier of a given CPU. Manufacturers have played around with how difficult it is to alter clock multipliers on their CPUs, and don't officially condone the idea, although it's worth noting that the current high-end CPUs, such as the Intel Core 2 Extreme, come with no lock on the clock multiplier.

In CPU manufacturing, manufacturers first test each CPU at the theoretical maximum speed it's capable of. If it passes, it's sold as a premium-priced, high speed chip. If it fails, it'll be tested at lower speed, and sometimes with specific functional operations disabled, until it's either running in a stable form -- and sold as a lower speed chip -- or junked altogether. From the manufacturer's point of view, the fewer chips they have to junk, the more profitable a given run of CPUs will be.

Because of this manufacturing economy, there is scope for overclocking chips, but be careful. No CPU manufacturer offers warranty support for overclocked chips, as there's a distinct danger of overheating a chip by running it faster than it's been safely clocked at. After all, if it ran well at that higher speed, it would be sold to market as a higher speed chip. Overclocking enthusiasts try to get around the increased heat output by changing the cooling arrangements within a PC to dissipate the extra heat. This can range from simply putting on a slightly larger heat sink and fan than the vendor supplied CPU fan all the way up to water-cooled semi-frozen PCs running at much higher speeds than would seem sensible.

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