Overclocking involves changing your computer system hardware settings to work at a faster speed than the manufacturer's rating. This can refer to the motherboard bus speed, the CPU speed, or both. Also called pushing or speed margining, the practice has become highly popularized, especially among gamers and modders.
Overclocking the CPU - In general CPU chips are tested by the manufacturer to see at what speed they fail.. They are then rated at a speed one step lower than this. Since the tests are quite stringent the idea is that it may be possible to push the CPU somewhat faster than its rating while maintaining stability in the system. Sometimes, when manufacturers are short on stock, they package faster GHz chips as slower ones; overclockers perceive this as a windfall.
Results from overclocking the CPU alone must be balanced against the rest of the system's specifications, namely the bus speed of the motherboard, memory, et cetera. For example, a 20% increase in processor speed does not usually translate to a 20% overall improvement. The CPU might be running faster than the rest of the system, operating in a "hurry up and wait" environment. Therefore the increase might deliver a nice benchmark improvement but little real-world difference.
Unsuccessful overclocking can result in an unstable system at best, and in the worst case scenario can damage the CPU. Though the latter is less common, it happens. Pushing also reduces the lifetime of the processor an indeterminable amount, as it forces the chip to work harder and hotter. Cooling fans and a good heatsink become even more important in this case.
Overclocking the System Bus - Changing the motherboard bus speed successfully can create a noticeable improvement on the entire system because all components will run faster. Since the processor's effectiveness is helped by the bus speed, an improvement here can also utilize the full benefit of the CPU. However, overclocking the system bus is risky because it means pushing every component on the motherboard.
Some people mistakenly believe that if a motherboard offers varying bus speed options they must be supported and therefore safe to use. The problem is that the components you install may not be tested at, or rated for the higher bus speed. Changing this setting affects the CPU (unless you adjust the clock multiplier), the chipset, memory bus, system cache, system memory, built-in IDE hard disk controllers, PCI I/O bus slots, and all peripherals. All components must be able to handle the change for the system to successfully perform without hardware failures. Manufacturer warranties do not cover problems created by overclocking.
While pushing a system might start out problem-free, several months down the road when components have aged due to use and temperature changes, instability can crop up. This is more likely to occur when the overclocking was already at the brink of what the system could withstand. When problems do arise — even a program crash — it can no longer be taken for granted that the crash is due to a software glitch. Troubleshooting a system that is overclocked can be an exercise in frustration. The variables increase exponentially and the ability to rule out potentials is made more difficult as hardware might be acting in unpredictable ways.
While overclocking is a hobby to some, and in many if not most cases proves to be nothing more than a benign self-upgrade, it may be worth considering whether you want to risk potential fallout for what is usually a relatively marginal improvement. If your system is running fine and you don't require the tweak it's probably safer to forgo it, all things considered. On the other hand if you'd like to learn more, there are various sites dedicated to overclocking.