Overclocking

The purpose of overclocking

A processor is normally designed to operate at a given frequency, namely the one for which its operation has been certified. It can, however, be advantageous to increase this frequency as it is what governs the processor's speed of computation. In this way, you can increasing your computing power without spending any money.

Furthermore, it is also possible to increase the frequency of the motherboard bus, in other words, the communication speed between the processor and other components.

This process of increasing the processor frequency is generally referred to as overclocking.

However, this process can also be dangerous for your computer. First of all, an increase in frequency is accompanied by an increase in temperature in the components whose frequency was increased. You therefore must make sure that the components affected by this increase in temperature are properly ventilated (the processor is one component that will obviously experience a major increase in temperature, but other components will be affected as well...). The first thing to do, therefore, is to add additional heat sinks / fans to evacuate the extra heat.

Furthermore, add-on cards may not be able to accept too great an increase in frequency (a PCI card, for example, is initially designed to operate at 33 MHz).

In a best-case scenario, the system will operate correctly. It may, however, become unstable or lock up, in which case you need to go back to the previous configuration. Some components may even overheat and burn, in which case you will need to change them and the process of overclocking could potentially become more expensive than changing the processor!

Understanding the concept of frequency

To understand overclocking, you need to understand the concept of frequency and the relationships that exist between the frequencies of the motherboard and the microprocessor.

First of all, you need to know how manufacturers determine the frequency at which the processor will operate:
the processors manufactured by a manufacturer all come from the same base series. However, after manufacturing the processors undergo frequency tests, which means that the processors are subjected to a given frequency and then the processor is checked to see if it operates stably. The processor may, however, be able to operate at a higher frequency, and this, in fact, is almost always the case, as manufacturers use a wide safety margin to guarantee the quality of their processors, and it is into that safety margin that you start encroaching when you push the processor to its limits in order to gain megahertz, the equivalent of computing power!
For example, a Pentium 150 will not be much different than a Pentium 166.

As the processor runs at a higher speed than the motherboard, there exists what is called a multiplier coefficient (or multiplication coefficient) that defines the processor speed in relation to the motherboard speed. A coefficient of 2 therefore means that: "the processor runs at double the frequency of the motherboard".

Overclocking can be achieved in two ways:

• by modifying the multiplier coefficient (the motherboard will not experience any change in frequency, only the processor will run at a higher speed)
• by modifying the base frequency, in other words, the motherboard's frequency (the processor will then also experience an increase in frequency proportional to the multiplier coefficient). The possible frequencies for the motherboard depend on the type of motherboard (a recent motherboard will obviously be capable of higher frequencies), but will be one of the following:
  • 50MHz
  • 60MHz
  • 66MHz
  • 75MHz
  • 83MHz
  • 100MHz
  • and higher...

Overclocking possibilities

Base processor	System bus (motherboard)	PCI bus	Multiplier Coefficient	Result
Pentium 75	60 MHz 66 MHz	30 MHz 33 MHz	1.5 1.5	Pentium 90 Pentium 100
Pentium 90	60 MHz 66 MHz	33 MHz 33 MHz	1.5 2	Pentium 100 Pentium 133
Pentium 100	66 MHz	33 MHz	2	Pentium 133
Pentium 120	66 MHz 66 MHz	33 MHz 33 MHz	2 2.5	Pentium 133 Pentium 166
Pentium 150	66 MHz 66 MHz	33 MHz 33 MHz	2.5 3	Pentium 166 Pentium 200
Pentium 166	66 MHz	33 MHz	3	Pentium 200

Which type of overclocking should you choose?

As mentioned above, there are two main ways of overclocking your system:

• overclocking the processor only
• overclocking the motherboard and all its components

So, which type of overclocking should you choose?

The frequency of a PCI-type bus, for example, is linked to the motherboard frequency by a coefficient of 0.5, which means that with a motherboard operating at 66MHz the PCI bus will have a frequency of 33MHz. So increasing the base frequency of the motherboard will have, as a direct consequence, a proportional increase in the frequency of the PCI bus, in other words on all the components that are attached to it.

It is therefore better to increase the motherboard than the multiplier coefficient. Lets look at an example: a Pentium 166 with a base frequency of 83MHz and a multiplier coefficient of 2 (2x83=166) will have better performance than a Pentium 200 with a base frequency of 66MHz and a multiplier coefficient of 3 (3x66=200). What happens is that certain components play the role of a brake, in that the processor "waits" until they have completed their operations before it continues with its own!

Cooling and aeration

As soon as you start overclocking, the temperature of the overclocked components becomes significantly higher, which could be harmful to them. A processor is normally tested to withstand a temperature on the order of 80°C, beyond which damage may be irreversible. That is why you can never talk about overclocking without also talking about cooling and aeration. A processor is usually cooled by a special-purpose fan. It is not, however, the only element that suffers from the overheating associated with overclocking: chipsets, memory modules, and voltage regulators must also be cooled.

Which cooling systems should you use?

The system most commonly used is a fan mounted on a heat sink (a heat sink is a metal plate with small fins that improves the heat exchange between the processor on which it is mounted and the ambient air). The fan can also be mounted directly on the processor, but the cooling will not be as effective; sometimes a small metal plate inserted between the fan and the processor can help to dissipate the processor heat. The fan must be as large as possible (use, for example, a Cyrix 6x86 M1 special fan, which is known for its heat dissipation) to allow major air movement which will also contribute to the ventilation of the case...

Some overclocking aficionados use a (silicon-type, heat-)conductive paste between the processor and the fan to achieve the best possible heat exchange. There are also fans that are equipped with an alarm (connected to the speaker of your computer) which will sound if the fan breaks down. In fact, a fan failure can directly cause the death of your processor. This type of fan is therefore recommended if you are severely overclocking your processor.
Finally, there are components designed to provide excellent cooling: these are Peltier effect plates, which act like a heat pump, by significantly lowering the temperature on one side (the processor side), but heating the other side, which must be cooled by a fan. This type of system is recommended for overclocking!

Aeration is also very important as it is air movement inside the case that makes it possible to evacuate the heat (transferred to the air from the components). For this reason, a well-arranged case minimises obstacles to ventilation. In particular, hard drive ribbon cables (particularly SCSI ribbon cables, which are very wide), if they are located in front of an element that heats up (the processor, for example), will obstruct air circulation and could cause overheating (even for processors that are not overclocked...).

In addition, the hard drive is also sensitive to excessive heat increases, so you must make sure that you don't locate it in a confined part of the case; instead it should be in an area where it will benefit from fan airflow.