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Overclocking

One of the ways that people try to get more bang for the buck out of their computer systems is a technique called overclocking. This involves 'tricking' the motherboard to push the CPU, memory or video processor at a higher speed than the manufacturer's official rating. The obvious benefit is higher performance. The disadvantages can include decreased reliability, voiding the warranty, and even burning out the processor or other components altogether. As is usually the case, the more you know about it the better your chances of getting the benefits while minimizing the hazards.

The clock signal applied to the processor is a combination of two factors. One of these is the basic internal clock speed of the system bus that connects the CPU and memory, sometimes called the Front-Side Bus or FSB. The second factor is the multiplier setting. In the old days the CPU and FSB always ran at the same speed, but as processors became faster the FSB speed was multiplied to provide a higher CPU clock. This multiplier is typically 2X or 3X and can be as high as 20X. You will also see fractional multipliers like 2.5X.

It's not rocket science. If the bus clock is 100 MHz and the multiplier is 2X, the effective CPU clock speed is 200 MHz (by the way, this is not necessarily the same as the CPU's rated speed, but that's the subject of another tech tip). To overclock your CPU, use either a higher bus speed or a higher multiplier. In this example, using a multiplier of 3X would increase the CPU clock to 300 MHz (and a 50% increase in CPU throughput, at least in theory). If you change the bus speed rather than the multiplier, smaller increments of change are possible. However, this also overclocks the memory and adapter cards, which are often less tolerant of these changes than the CPU.

The bus speed and multiplier settings are changed either in the CMOS or by a jumper on the motherboard, but some manufacturers do not provide any way to overclock. If you buy a brand-name system from Dell, IBM, HP, Gateway or others using an Intel CPU you will probably find that the bus speed and multiplier are 'clock-locked', although there are hardware modifications to get around this. On the other hand, systems with the AMD Athlon or Duron processors are favoured by overclockers for the ease of changing these values. This is also true of most after-market motherboards. Some motherboard manufacturers even provide a Windows-based program that lets you try different clock/multiplier combinations to see how far you can push it.

The big hazard with overclocking is heat. The faster a chip works, the more heat it generates. The hotter the chip, the more errors it will make, and the faster it will burn out. The CPU chip makers try to leave a Comfortable margin, so you can often get away with about a 25% increase in the CPU speed with no additional modifications.

Any more than that and you need to find a way to remove more heat from the system. A well-ventilated case and a powerful heat-sink fan for the CPU make a good start, and you might want to get a temperature probe so you can monitor the results. If you raise the bus speed very far, instead of just changing the multiplier, heat-sinked memory modules are a must. In that case you'd also better pay attention to the temperature on the NIC and video cards.

For about £100 you can even water-cool your system, and you don't have to replace too many burned-out CPU chips before that starts looking like a really good investment. By the way, our Micro-Scope diagnostic software will allow you to easily monitor the fan speed as well as CPU temperature and voltages on properly quipped motherboards.

So, now that you can walk the walk, you need to talk the talk. Here are some common terms used by the overclocking crowd:

Like, my next mobo mods will need a bigger HSF so I can O/C the FSB without a total crash and burn. Word, man!