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[ The PC Guide | System Optimization and Enhancement Guide | Overclocking: The Dissenting Opinion | Introduction to Overclocking ]

Overclocking Types

There are three primary ways that you can overclock a modern PC: you can overclock the processor, you can overclock the system bus, or you can overclock both. Overclocking the system bus is more complicated than overclocking the processor, because it requires special support from the motherboard, and because doing it causes several other components in the system to also be overclocked.

Modern processor speeds are determined by the system (memory) bus speed, and the clock multiplier used to determine the clock rate of the processor relative to that bus speed. For example, a standard Pentium 150 is designed to run on a 60 MHz system bus, with a multiplier of 2.5. Overclocking is accomplished by changing these settings. Here is a table that shows how the three different types of overclocking work:

Overclocking Type

System Bus Speed

Processor Multiplier

Processor Speed

Normal Setup

60 MHz


150 MHz

Processor Overclocking

66 MHz


166 MHz

60 MHz


180 MHz

System Bus Overclocking

75 MHz


150 MHz

Processor and System Bus Overclocking

75 MHz


187 MHz

As you can see, there are a lot of options with a 150 MHz chip such as this, but it all depends on the motherboard that the system is placed into. For example, most standard Pentium motherboards don't support a 75 MHz bus speed setting; the standard limit is 66 MHz. In addition, some motherboards are limited in the clock multiplier settings they will support. You can't overclock a Pentium 200 to 233 if your motherboard only supports a maximum clock multiplier of 3x.

I've given two examples for processor overclocking here; in both cases I consider these overclocking only the processor, because the system bus speed is kept to 66 MHz or less, the traditional standard for Pentium motherboards. The 75x2 situation means that you are overclocking only the system bus (and associated components) while leaving the processor at its nominal 150 MHz. In the last case, both are being overclocked. Of course with a newer 100 MHz motherboard, system bus speeds of up to 100 MHz are officially supported.

Note: Overclocking the system bus means overclocking many different components in your PC, which some people do not realize.

Next: Overclocking Risks and Rewards

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