Overclocking
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Overclocking is making a computer component run at a higher clock speed than the manufacturer's specification. Although there are many different reasons for overclocking, the most popular reason is to increase hardware performance. Overclocking can result in system instablity and sometimes even hardware failure if done carelessly.
Overclocking is mostly practiced by PC enthusiasts in order to realize the full potential of their computers. Some hardware enthusiasts purchase a low-end computer and overclock it, thereby attaining performance of a higher-end system, while others will overclock high end components, attaining unprecedented performance. The fastest home computers in the world are overclocked and often a non-overclocked computer is slower than an overclocked one.
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Considerations for overclocking
The main requirement of overclocking is an effective cooling system to remove the excess heat overclocked components emit. Because most coolers are designed for the heat a non-overclocked component produces, overclockers typically purchase high quality cooling systems. Copper heatsinks in combination with powerful fans provide better cooling than OEM coolers. Water cooling is used as well, which when properly implemented provides much more powerful cooling then heatsink/fan combinations.
System stablity is a major concern when overclocking. Without proper cooling, an overclocked component can overheat and crash. Stress tests (also known as burn-in) can be used to test system stablity. A stress test places a high load on the component being overclocked. Programs commonly used for stress testing are Super-Pi, Prime95, SiSoft Sandra.
Commonly overclocked components include: processors, video cards, motherboard chipsets, and RAM. Methods that have been used to cool overclocked components include: forced convection (a fan blowing onto a surface); liquid cooling (liquid carries waste heat to a radiator, similar to how automobile engines are cooled); liquid nitrogen (perhaps the most dangerous method); dry ice; phase change cooling (as used in refrigerators); and submersion (placing the entire computer in an inert fluid). Liquid nitrogen is a temporary cooling measure in most cases, since a sufficient supply of power to maintain the LN2 coolant at liquid state is uneconomical. Because of this, liquid nitrogen (or dry ice, for that matter) is used as an extreme measure to set a record in a one-off experiment rather than to cool a system for a normal period of use. One reason is the cost of these extreme cooling methods, or usually because the hardware exposed to such cooling is ironically destroyed in the process. Of the aforementioned methods, air cooling, liquid cooling, and phase cooling are the most popular, due to their efficiency, availability, and affordability.
Overclocking arises in part due to the economics of the manufacturing processes of CPUs. In most cases, CPUs with different rated clock speeds are manufactured via exactly the same process. A batch of CPUs may be tested and binned--that batch is set to operate at a specific frequency because all of the processors function at that clockspeed. The clock speed that the CPU is marketed under is the speed at which the CPU has been tested to operate consistently well, but often there is a distribution where on one end there are the CPUs which are near their physical limit at the specified clockspeed and on the other end there are CPUs which can operate at frequencies substantially higher than their specifications. With proper power and cooling, slower CPUs can be made to run at the same speed, or faster, than similar CPUs with higher stock clockspeeds. A commonly held view is that overclocking results in system instability. This is rarely the case when the system is properly tested and the temperature and voltages are monitored.
In addition, there have been situations in which a chip manufacturer will deliberately underrate a chip in response to market pressure. This results in an inexpensive component, which (with a little extra voltage) is easily overclocked to match the speed of a more expensive component. One example is the AMD Athlon XP 2500 (codename Barton) processor, which was easily made as fast as the AMD Athlon XP 3200 , which was four times as expensive at the time.
Recently computer experts experimented with a Pentium 4 3.4 GHz HT processor, cooling it using liquid nitrogen, and blowing cold air at high speeds past it. They managed to achieve over 3 GHz above the original frequency, which is a considerable amount. Of course, it is cheaper, more energy efficient and convenient to use a dual processor computer than to overclock a single processor to these speeds. Very few users would tolerate regularly topping off their computer with liquid nitrogen, but even the noise of such a system would make it unsuitable for many practical uses. These tests are interesting, however, as an illustration of what is possible when great amounts of heat can be removed from a system and are an indication of what could be achieved with better (but not as drastic) heat sinking.
Measuring effects of overclocking
For some overclockers, the increased clock statistics are a reward in themselves, while others take the more pragmatic view that perceptible improvements are necessary to justify the effort. Human judgment on the speed of a computer is inherently subjective and open to the placebo effect, therefore there are many de facto benchmarks used to evaluate performance. The benchmarks can themselves become a kind of 'sport', in which users compete for the highest scores.
Given only benchmark scores it may be difficult to judge the difference overclocking made to the computing experience. Some benchmarks test only one aspect of the system, such as Random Access Memory bandwidth, without taking into consideration how faster speeds in this aspect will improve the system as a whole; memory bandwidth is typically not a bottleneck, apart from 'serious tasks' like video encoding, high-demand databases and scientific computing. Other benchmarks, such as 3D Mark attempt to replicate game conditions, but because some tests involve non-deterministic physics, such as ragdoll motion, the scene is slightly different each time and small differences in test score are overcome by the noise floor. Most overclocking sites use recorded demos of recent games for benchmarks, which give a good indication of the performance in that game, but are still not completely realistic because the system does not have to perform physics calculations.
Overclocking by resellers
Commercial system builders or component resellers sometimes overclock to sell items at higher profit margins. By buying lower-value components, overclocking them, and selling on as higher value ones, the retailer makes more money. In some cases an overclocked component is functionally identical to a factory-clocked one, especially if it was deliberately underrated by the manufacturer; however, it is generally considered dishonest if the customer is not told they are buying overclocked equipment. It is felt that because of a risk of shortened component lifespan, the customer be allowed the informed choice to use overclocked components or not.
Overclocking is sometimes seen as a legitimate service, in which a company tests the 'overclockability' of individual items rather than the customer just buying and hoping theirs will overclock well. One example is the retailer who checks which GeForce 6800 cards work correctly with extra pixel shaders unlocked (effectively making it a 6800 ultra), and charges slightly above the retail price for the cards known to work. Many specific 'tricks of the trade' such as this are highly dangerous and can render hardware non-functional, though they are attractive since as with all overclocking, the user is getting a 'free lunch'. Simple feature unlocking such as this can often be done by simply joining two points on a circuit with a graphite pencil (known as the pencil tick)
Of course, manufacturers would like high performance seekers to pay extra for high-end products, but also fear that less reliable components and shortened life span would damage brand image. It is mainly fear of this kind of practice that motivates major manufacturers to design overclocking prevention mechanisms such as CPU locking. These measures are claimed to be customer protection, which often meets a mixed reception.
Advantages of overclocking
- You can, in many cases, purchase a slower component for a cheaper price and overclock it to the speed of a more expensive component.
- Faster performance in games and applications for free. This can lead to higher scores in some games, especially the very popular multiplayer modes in first person shooters.
- General computing tasks can be made faster, eg. booting up, moving files, and installing an operating system.
- Overclocking can go a step beyond making games and applications perform better, making it possible for them to run at all. For example, the difference between 20 frames per second and 25 frames per second can make a game seem much more smooth and playable, and would only require a 25% overclock, often only on the component that is the bottleneck.
- 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 speed of four units of RAM to 333 MHz. However, the memory speed is computed by dividing the processor speed (which is a base number times a multiplier, for instance 1.8 GHz is most likely 9x200 MHz) by a fixed integer such that, at stock speeds, the RAM would run at a clock rate near 333 MHz. Manipulating elements of how the processor speed is set (usually lowering the multliplier), one can often overclock the processor a small amount, around 100-200 MHz (less than 10), and gain a RAM clock rate of 400 MHz (20% increase), realizing the full potential of the RAM.
- Overclocking can be an engaging hobby in itself and supports several dedicated online communities such as those listed below.
- Overclocking is often seen as a rite of passage, a mark of prestige, and/or a way to indentify oneself in the gaming culture.
Disadvantages of overclocking
- Increasing the clock speed and/or voltage of a component can shorten its lifespan and possibly damage its circuitry.
- Increasing the clock speed of a component increases its power consumption or electrical "workload", which causes a rise in temperature. If the temperature rises too high the component can fail. In some situations, laptop computers running on battery power for example, the rise in power consumption may also be a problem.
- More common than hardware damage is crashing, although it often possible to reboot the system after leaving it to cool for a short time. Although the hardware is not permanently damaged, this is inconvenient and could cause data loss. In rare, extreme cases entire filesystem failure may occur, causing the loss of all data. The risk of losing data can be lessened (though not eliminated) by using a journaling filesystem or redundant storage.
- Not every component of a computer is overclockable; for example, hard drive platters cannot be made to spin any faster. Where hard drive read/write rate is the bottleneck, as it often is, overclocking brings little or no speed advantage.
- Personal computers are mostly used for tasks which do not push the hardware, or where the speed of a task is restricted by bottlenecks outside of the local machine. For example, web browsing does not require a very fast computer, and the limiting factor will almost certainly be the speed of the internet connection. Other general office tasks such as word processing and sending email are more dependent on the efficiency of the operator than on the speed of the hardware. In these situations any speed increases through overclocking are unlikely to be noticeable.
- It is generally accepted that, even for computationally-heavy tasks, speed increases of less than ten percent are difficult to discern. For example, when playing video games, most people would fail to notice an increase from 60 to 66 frame/s without the aid of an on-screen frame counter. Generally, gains of a few percent are sought for prestige rather than real-world computational benefit.
- Products sold specifically for overclocking are sometimes just decoration. Although this is not a bad thing in itself, buyers should be aware of the marketing hype surrounding some products. Examples include heat spreaders and sinks designed for chips which do not generate problematic amounts of heat.
- Powerful fans create much noise, which may make them unsuitable for desktop use. Quiet overclocking can be difficult, although specialised products are available. Generally it is possible to make a component quieter or faster, but both is a considerable challenge. Some people do not mind the extra noise, and it is common for overclockers to have computers much louder than stock machines. In HTPC situations noise is critical, so overclocking is not advisable. Quieter options for overclockers include liquid and phase-change cooling.
- Overclocking will not necessarily save money. Non-trivial speed increases often require premium cooling equipment, and once the hobby bites it can become an expensive pastime. Most people who consider themselves overclockers spend significantly more on computer equipment than the average person.
- If computing power doubles roughly every 18 months (see Moore's Law) then it increases by around 4% per month (because <math>1.04^{18}\approx2<math>). Therefore, given a 10% overclock, stock machines will have caught up in less than three months. A more ambitious overclock will keep the overclocker ahead for longer, but may be very difficult to do. To be six months ahead, the overclocker would need to make their hardware run more than 25% faster. Overclocking by 25% is possible with mid-range hardware, but almost unheard of with high-end equipment.
- Overclocking usually results in the voiding of hardware manufacturer's warranties.
Overclockers
An overclocker is generally defined as someone who overclocks his or her computer. The term overclocker has grown to include a wider group of people. Overclocking is still a very prolific hobby. With cooling methods becoming more advanced and with inexpensive microprocessors being produced with the same core circuitry as faster microprocessors of the same series, many do-it-yourself computer builders overclock to some extent.
External links
Some web sites that provide information on overclocking or serve as a community for overclockers include:
- Anandtech (http://www.anandtech.com)
- Tom's Hardware Guide (http://www.tomshardware.com)
Overclocking forums:
- Overclockers.com.au (http://forums.overclockers.com.au/forums)
- OCForums.com (http://www.ocforums.com/)
- ExtremeOverclocking (http://forums.extremeoverclocking.com/)
- HardOCP (http://www.hardforum.com/)
- VR-Zone (http://www.vrforums.com/)
- XtremeSystems.org (http://www.xtremesystems.org/forums)
- Overclock.net (http://www.overclock.net/)
Online databases with detailed information of overclocked systems:
- Overclockers.com CPU Database (http://www.cpudatabase.com)
- VR-Zone Overclocking Database (http://www.vr-zone.com/ocdb/)
See also
- CPU locking
- Front side bus
- Underclocking
- OverDrive
- CPU cooling
- PC motherboard
- Overvolting
- Computer coolingid:Overclock
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