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What Is CPU Overclocking?

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.

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


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."

Vangie 'Aurora' Beal
Last updated: September 16, 2005

Related Links

(1)  Source: Overclockers New Zealand Forums

Overclockers New Zealand Forums
An excellent FAQ with instructions, descriptions, and background information on overclocking a CPU. Provides example changes and an excellent plan and test section. This FAQ was referenced in our article.

SysOpt Overclocking Database
Search through the data to find out the "overclockability" of various hardware configurations.

Tom's Blurb: Overclocking AMD's Socket A Processors
I've got even two things to report for the ones of you who don't just fancy AMD's new Duron and Athlon/Thunderbird processors because they are good performers for a fair price, but who like to tweak some more speed out of them with overclocking.

The FiringSquad - Home of the Hardcore Gamer
The first big steps towards overclocking were made in the Pentium era. During this time, typical neighborhood techies discovered that a Pentium 75 was nothing more than an underclocked Pentium 90. Soon, people were taking Pentium 133s and turning them into 166s, and in turn 166s soon became 200s. When the 233MMX made an entrance, it soon became obvious that the chip had little trouble reaching 250MHz or 266MHz.

Value Overclocking: Celeron D 335 vs. Sempron 3100+
It has been a long time since both Intel and AMD released value processor lines with so much promise. Both the Celeron D and Sempron (Socket 754) models are variants of popular high-end core designs, and not only provide a nice performance increase over last-generation designs, but look to have serious overclocking potential.

Hardware Central - CPU Overclocking
Overclocking is going mainstream, it seems, among end users. Almost all hardware Web sites discuss the subject, and most make it seem like it's easy, and that everyone does it. Of course, manufacturers don't want you to do it to their processors, so you probably won't find it mentioned in magazines. But, on the Internet, it runs rampant. In many cases, though, you don't get the real story behind it.

Pentium 4 Northwood Overclocking Guide
The Pentium 4 Northwood core provides the required "new core" ingredient, while many highly overclockable and 533 MHz-compatible platforms give users a great overclocking base to work with.

CyberCPU How-to
This article reviews the essential notions and basic steps on How To overclock your computer.

Gamer God - Keeping it Cool
An excellent overview of Cooling. - JUMPERS
The two values that determine the speed of the processor (frequency of the bus or clock and multiplier) are found on the motherboard. The method used to change them depends on the model of motherboard itself.

Athlon XP Overclocking Guide
This Athlon XP Overclocking Guide will take you through the two main overclocking methodologies, and give you the basic steps you'll need to either start your overclocking journey or just refine your current system setup.

Intel Processors Frequency ID Utility
The Intel Processor Frequency ID Utility was developed by Intel Corporation to identify characteristics of the processor inside a system assuring the processor is operating at the tested and rated frequency intended by Intel Corporation. This ensures your processor is exactly what you ordered and not an overclocked model.