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What Is CPU Overclocking?

Vangie Beal
Last Updated May 24, 2021 8:01 am

While the words CPU and microprocessor are used interchangeably, in the world of personal computers (PC), a microprocessor is actually a silicon chip that contains a CPU. At the heart of all personal computers sits a microprocessor that controls the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles. The three basic characteristics that differentiate microprocessors are the following:

  • Instruction set: The set of instructions that the microprocessor can execute.
  • Bandwidth: The number of bits processed in a single instruction.
  • Clock speed: Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

The higher the value, the more powerful the CPU. For example, a 32-bit microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz.

If you think overclocking sounds like an ominous term, you have the right idea. Basically overclocking means to run a microprocessor faster than the clock speed for which it has been tested and approved. Overclocking is a popular technique for getting a little performance boost from your system, without purchasing any additional hardware. Because of the performance boost overclocking, is very popular among hardcore 3D gamers.

Most times overclocking will result in a performance boost of 10 percent or less. For example, a computer with an Intel Pentium III processor running at 933MHz could be configured to run at speeds equivalent to a Pentium III 1050MHz processor by increasing the bus speed on the motherboard. Overclocking will not always have the exact same results. Two identical systems being overclocked most likely will not produce the same results. One will usually always overclock better than the other.

To overclock your CPU you must be quite familiar with hardware, and it is always a procedure conducted at your own risk. When overclocking there are some problems and issues you’ll have to deal with, such as heat. An overclocked CPU will have an increased heat output, which means you have to look at additional cooling methods to ensure proper cooling of an overclocked CPU. Standard heat sinks and fans will generally not support an overclocked system. Additionally, you also have to have some understanding of the different types of system memory. Even though your CPU can be overclocked, it doesn’t mean your RAM modules will support the higher speeds.

Common CPU Overclocking Methods

The most common methods of overclocking your CPU is to either raise the multiplier or raise the FSB (frontside bus) while not the only options they are the most common. To understand overclocking, you have to understand the basics of CPU speeds. The speed of a CPU is measured in Megahertz (MHz) or Gigahertz (GHz). This represents the number of clock cycles that can be performed per second. The more clock cycles your CPU can do, the faster it processes information.

The formula for processor speed is: frontside bus x multiplier = processor speed.

(1) Pentium III 450MHz
The CPU runs at 450 million clock cycles per second. The CPU runs at at a speed of 450 megahertz. Using our processor speed equation we have: 100MHz (frontside bus) x 4.5 (multiplier) = 450MHz (processor speed)

The frontside bus connects the CPU to the main memory on the motherboard basically, it’s the conduit used by your entire system to communicate with your CPU. One caution with raising the FBS is that is can affect other system components. When you change the multiplier on a CPU, it will change only the CPU speed. If you change the FSB you are changing the speed at which all components of your system communicate with the CPU.

Using our example above, the multiplier is 4.5. Since valid multipliers end in .0 or .5, you could try increasing the multiplier to 5.0 to obtain a performance boost (which would result in 100MHz x 5.0 = 500MHz). By far the easiest way to overclock a CPU is to raise the multiplier, but this cannot be done all all systems. The multiplier on newer Intel CPUs cannot be adjusted, leaving Intel overclockers with the FSB overclocking method (because of this AMD is becoming more of a popular choice for overclockers). The equation formula doesn’t change for the method of raise the FSB. In the example above the FSB was 100MHz. Raising it to 133Mhz would change the equation (133Mhz x 4.5 = 598.5 MHz).

Sometimes overclocking can be that simple — other times it’s not.

Depending on your motherboard, overclocking is done one of three ways: by changing jumper or dip-switch settings (from .on. and .off. or .close. and .open.), by changing some of the Chipset Features settings in your BIOS, or by using a combination of both. In overclocking you will need to know your hardware, plan your overclocking method, and, of course perform many tests once changes have been made. You may need to adjust your CPU voltage, and you will most likely have to try several settings before obtaining a successful and stable overclock result.

Overclocking Risks (and There Are Many)

Overclocking comes with many risks, such as overheating, so you should become familiar with all the pros and cons before you attempt it. Additionally, overclocking isn’t supported by the major chip manufacturers which means overclocking your CPU will void your warranty. Overclocking can also decrease the lifespan of the CPU, cause failure in critical components and may even result in some data corruption. You may also notice an increase in unexplainable crashes and freezes.

You can find many complete step-by-step guides available online that detail the actual process of overclocking. If you’ve decided to take the plunge and overclock your CPU, we recommend you don’t start with your only usable system (try using outdated and cheap hardware to practice with) and be sure to find a knowledgeable source and read some of the overclocking information and Web pages listed below in the links section to get you started in the right direction.

Did You Know…
“Multiplier locking forces the CPU to use a multiplier that is preset by the manufacturer. Intel has been quoted as saying they use multiplier locking to prevent unscrupulous retailers from overclocking processors to higher speeds, and selling overclocked systems to consumers for the same, higher price as the faster retail model.”

Key Terms To Understanding Overclocking

Abbreviation of central processing unit. The CPU is the brains of the computer.

To run a microprocessor faster than the speed for which it has been tested and approved.

frontside bus
The bus that connects the CPU to main memory on the motherboard.

More Overclocking Related Terms

clock speed
clock cycle

Based in Nova Scotia, Vangie Beal is has been writing about technology for more than a decade. She is a frequent contributor to EcommerceGuide and managing editor at Webopedia. You can tweet her online @AuroraGG.

This article was originally published on September 16, 2005