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Overclocking is configuration of computer hardware components to operate faster than certified by the original manufacturer, with "faster" specified as clock frequency in megahertz (MHz) or gigahertz (GHz). Commonly operating voltage is also increased to maintain a component's operational stability at accelerated speeds. However semiconductor devices operated at a higher frequencies and voltages generate additional heat, so most overclocking attempts increase power consumption and heat. An overclocked device may be unreliable or fail completely if the additional heat load is not removed or power delivery components cannot meet increased power demands. Many device warranties state that overclocking and/or over-specification voids any warranty.
The purpose of overclocking is to gain additional performance from a given component by increasing its operating speed. Normally, on modern systems, overclocking is targeted at increasing the performance of a major chip or subsystem, such as the main processor or graphics controller, but other components, such as system memory (RAM) or system buses (generally on the motherboard), are commonly involved. The trade-offs are an increase in power consumption (heat) and fan noise (cooling) for the targeted components. Most components are designed with a margin of safety to deal with operating conditions outside of a manufacturer's control; examples are ambient temperature and fluctuations in operating voltage. Overclocking techniques in general aim to "trade" this safety margin by setting the device to run in the "higher end" of the margin, with the understanding that temperature and voltage must be more strictly monitored and controlled by the user as the remaining "safety cushion" is reduced. Examples are that operating temperature would need to be more strictly controlled with increased cooling, as the part will be less tolerant of increased temperatures at the higher speeds; also base operating voltage may be increased to compensate for unexpected voltage drops and to strengthen signalling and timing signals, as low-voltage excursions are more likely to cause malfunctions at higher operating speeds.
While most modern devices are fairly tolerant of overclocking, all devices have finite limits, generally for any given voltage most parts will have a maximum "stable" speed where they still operate correctly. Past this speed the device starts giving incorrect results, which can cause malfunctions and sporadic behavior in any system depending on it. While in a PC context the usual result is a system crash, more subtle errors can go undetected, which over a long enough time can give unpleasant surprises such as data corruption (incorrectly calculated results, or worse writing to storage incorrectly) or the system failing only during certain specific tasks (general usage such as internet browsing and word processing appear fine, but any application wanting advanced graphics crashes the system).
- Not to be confused with overclocking(mileometer/odometer)
- The user can, in many cases, purchase a lower performance, cheaper component and overclock it to the clock rate of a more expensive component.
- Higher performance in games, encoding, video editing applications, and system tasks at no additional expense, but with increased electrical power consumption and thermal output.. Overclocking can extend the useful life of older equipment.
- Some systems have "bottlenecks," where small overclocking of a component can help realize the full potential of another component to a greater percentage than the limiting hardware is overclocked. For instance, many motherboards with AMD Athlon 64 processors limit the clock rate of four units of RAM to 333 MHz. However, the memory performance is computed by dividing the processor clock rate (which is a base number times a CPU multiplier, for instance 1.8 GHz is most likely 9×200 MHz) by a fixed integer such that, at a stock clock rate, the RAM would run at a clock rate near 333 MHz. Manipulating elements of how the processor clock rate is set (usually lowering the multiplier), it is often possible to overclock the processor a small amount, around 100–200 MHz (less than 10%), and gain a RAM clock rate of 400 MHz (20% increase in RAM speed, though not in overall system performance).
- Some people overclock for its own sake, for pleasure. The PCMark website and others host online communities dedicated to overclocking.
- The lifespan of semiconductor components may be reduced by increased voltages and heat. Warranties may be voided by overclocking.
- Increased clock rates and voltages increase power consumption, increasing electricity cost and heat production. The excess heat increases the ambient air temperature within the system case, which may affect other components. The hot air blown out of the case will heat the room it is in.
- An overclocked computer which works correctly may misbehave at future configuration changes. For example, Windows may appear to work with no problems, but when it is re-installed or upgraded, error messages may be received such as a “file copy error" during Windows Setup. Microsoft says this of errors in upgrading to Windows XP: "Your computer [may be] over-clocked." Because installing Windows is very memory-intensive, decoding errors may occur when files are extracted from the Windows XP CD-ROM.
- High-performance fans running at maximum speed used for the required degree of cooling of an overclocked machine can be noisy, some producing 50 dB or more of noise. When maximum cooling is not required, in any equipment fan speeds can be reduced below the maximum: fan noise has been found to be roughly proportional to the fifth power of fan speed; halving speed reduces noise by about 15 dB. Fan noise can be reduced by design improvements, e.g. by designing fans with aerodynamically optimized blades for smoother airflow, reducing noise to around 20 dB at approximately 1 metre. Larger fans rotating more slowly, which produce less noise than smaller, faster fans with the same airflow, can be used. Acoustical insulation inside the case, e.g. acoustic foam, can reduce noise. Additional cooling methods which do not use noisy fans can be used, such as liquid and phase-change cooling.
- Increasing the operation frequency of a component will usually increase its thermal output in a linear fashion, while an increase in voltage usually causes heat to increase quadratically. Excessive voltages or improper cooling may cause chip temperatures to rise almost instantaneously, causing the chip to be damaged or destroyed.
- Exotic cooling methods used to facilitate overclocking such as water cooling are more likely to cause damage if they malfunction. Sub-ambient cooling methods such as phase-change cooling or liquid nitrogen will cause water condensation, which will cause damage unless controlled.
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