What is Overclocking? Should You Ever Overclock Your Computer?

Why you might want to overclock your computer for better performance

Many people probably don't know what overclocking is but have possibly heard the term used before. Learn what it is and whether or not it's something you should try on your computer.

What is Overclocking?

To put it in its simplest terms, overclocking is taking a computer component such as a processor and running at a specification higher than rated by the manufacturer. In other words, you can run your computer harder and faster than it was designed to run if you overclock it.

Companies such as Intel and AMD rate every part they produce for specific speeds. They test the capabilities of each one and certify it for that given speed. The companies underrate most parts to allow for increased reliability. Overclocking a part takes advantage of its remaining potential.

A computer processor balancing on a finger.
 

Why Overclock a Computer?

The primary benefit of overclocking is additional computer performance without the increased cost. Most individuals who overclock their system either want to try and produce the fastest desktop system possible or to extend their computer power on a limited budget. In some cases, users can boost their system performance by 25 percent or more. For example, a person may buy something like an AMD 2500+ and, through careful overclocking, end up with a processor that runs at the equivalent processing power as an AMD 3000+, but at a significantly reduced cost.

Gamers often like to overclock their computers. If that interests you, read How to Overclock a GPU for Epic Gaming.

There are drawbacks to overclocking a computer system. The biggest drawback to overclocking a computer part is that you are voiding any warranty provided by the manufacturer because it is not running within its rated specification. Pushing overclocked components to their limits tends to result in reduced functional lifespan or even worse if improperly done, catastrophic damage. For that reason, all overclocking guides on the internet will have a disclaimer warning individuals of these facts before telling you the steps to overclocking.

Bus Speeds and Multipliers

All CPU processor speeds are based on two distinct factors: bus speed and multiplier.

The bus speed is the core clock cycle rate that the processor communicates with items such as the memory and the chipset. It is commonly rated in the MHz rating scale, referring to the number of cycles per second at which it runs. The problem is the bus term is used frequently for different aspects of the computer and will likely be lower than the user expects.

For example, an AMD XP 3200+ processor uses a 400 MHz DDR memory, but the processor uses a 200MHz frontside bus that is clock doubled to use 400 MHz DDR memory. Similarly, a Pentium 4 C processor has an 800 MHz frontside bus, but it's actually a quad pumped 200 MHz bus.

The multiplier is the actual number of processing cycles a CPU will run in a single clock cycle of the bus speed. So, a Pentium 4 2.4GHz "B" processor is based on the following:

133 MHz x 18 multiplier = 2394MHz or 2.4 GHz

When overclocking a processor, these are the two factors that can influence the performance. Increasing the bus speed will have the greatest impact as it increases factors such as memory speed (if the memory runs synchronously) as well as the processor speed. The multiplier has a lower impact than the bus speed, but can be more difficult to adjust.

Here's an example of three AMD processors:

CPU Model Multiplier Bus Speed CPU Clock Speed
Athlon XP 2500+ 11x 166 MHz 1.83 GHz
Athlon XP 2800+ 12.5x 166 MHz 2.08 GHz
Athlon XP 3000+ 13x 166 MHz 2.17 GHz
Athlon XP 3200+ 11x 200 MHz 2.20 GHz

Here are two examples of overclocking the XP2500+ processor to see what the rated clock speed would be by changing either the bus speed or the multiplier:

CPU Model Overclock Factor Multiplier Bus Speed CPU Clock
Athlon XP 2500+ Bus Increase 11x (166 + 34) MHz 2.20 GHz
Athlon XP 2500 + Multiplier Increase (11+2)x 166 MHz 2.17 GHz

Because overclocking was becoming a problem from some unscrupulous dealers who were overclocking lower-rated processors and selling them as higher-priced processors, the manufacturers started to implement hardware locks to make overclocking more difficult. The most common method is through clock locking. The manufacturers modify traces on the chips to run only at a specific multiplier. A user can defeat this protection by modifying the processor, but it is much more difficult.

Managing the Voltage

Every computer part has a specific voltage for its operation. During the overclocking process, the electrical signal might degrade as it traverses the circuitry. If the degradation is enough, it can cause the system to become unstable. When overclocking the bus or multiplier speeds, the signals are more likely to get interference. To combat this, you can increase the voltage to the CPU core, memory, or AGP bus.

There are limits to how much more a user can apply to the processor. If you apply too much, you could destroy the circuits. Typically this is not a problem because most motherboards restrict the setting. The more common issue is overheating. The more you supply, the higher the thermal output of the processor.

Dealing With Heat

The biggest obstacle to overclocking the computer system is overheating. Today's high-speed computer systems already produce a large amount of heat. Overclocking a computer system compounds these problems. As a result, anyone planning to overclock their computer system should understand the requirements for high-performance cooling solutions.

The most common form of cooling a computer system is through standard air cooling: CPU heatsinks and fans, heat spreaders on memory, fans on video cards, and case fans. Proper airflow and suitable conducting metals are vital to the performance of air cooling. Large copper heatsinks tend to perform better, and extra case fans to pull air into the system also help to improve cooling.

Beyond air cooling, there is liquid cooling and phase change cooling. These systems are far more complex and expensive than standard PC cooling solutions, but they offer higher performance at heat dissipation and generally lower noise. Well-built systems can allow the overclocker to push the performance of their hardware to its limits, but the cost can end up being more expensive than the processor cost. The other drawback is liquids running through the system that can risk electrical shorts damaging or destroying the equipment.

Component Considerations

There are a lot of factors that will affect whether you can overclock a computer system. The first and foremost is a motherboard and chipset that has a BIOS that allows the user to modify the settings. Without this capability, it's not possible to alter the bus speeds or multipliers to push the performance. Most commercially available computer systems from the major manufacturers do not have this capability. Those interested in overclocking tend to buy parts and build computers.

Beyond the motherboard's ability to adjust CPU settings, other components must also be able to handle the increased speeds. Buy memory that is rating or tested for higher speeds to preserve the best memory performance. For example, overclocking an Athlon XP 2500+ frontside bus from 166 MHz to 200 MHz requires that the system have PC3200- or DDR400-rated memory.

The frontside bus speed also regulates the other interfaces in the computer system. The chipset uses a ratio to reduce the frontside bus speed to match the interfaces. The three primary desktop interfaces are AGP (66 MHz), PCI (33 MHz), and ISA (16 MHz). When the frontside bus is adjusted, these buses will also be running out of specification unless the chipset BIOS allows for the ratio to be adjusted down. Keep in mind that changing the bus speed can impact stability through the other components. Of course, increasing these bus systems can also improve the performance of them, but only if the parts can handle the speeds. Most expansion cards are very limited in their tolerances, though.

If you're new to overclocking, don't push things too far right away. Overclocking is a tricky process involving a lot of trial and error. It is best to thoroughly test the system in a taxing application for an extended period to ensure the system is stable at that speed. At that point, step things back a bit to give some headroom to allow for a stable system that has less chance of damage to the components.