Overclocking is the practice of making a component run at a higher clock speed than the manufacturer's specification. The idea is to increase performance for free or to exceed current performance limits, but this may come at the cost of stability.
Overclocking is mostly practiced by PC enthusiasts in order to squeeze the most performance out of their machines. Some enthusiasts will do this so they can buy a lower-end system, overclock it, and achieve the performance of a higher-end system. However, the cost of an adequate cooling system, and often even the cost of choice overclocking components results in a base of overclockers who mostly overclock as a hobby, or as a 'sport' of sorts - always striving for more speed.
Many enthusiasts will purchase high-end components to begin with, and then overclock them to achieve even more performance. The fastest home computers in the world are overclocked, and a stock (running at manufacturer's specifications) system is often no match for an overclocked one.
Considerations for overclocking
The main aspect of overclocking is the need for more effective cooling than that of air-based cooling systems which come packaged with typical CPUs and graphics cards. High-end, specially-designed, copper heatsinks are often used with powerful fans for better cooling. Liquid (usually water) cooling is another popular method, because by using liquid to move heat to a large radiator, more heat can be removed than by using air alone. Instability is a major danger of overclocking, although most overclockers take some precautions to check their systems for stability. The process of stress-testing a system is often called burn-in, and it is common to run several applications simultaneously or special burn-in application that place a high load on the component being tested.
Commonly overclocked components include: CPUs, 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. There is a commonly held view that overclocking results in system instability. This is not 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 bit of 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 is easily made as fast as the AthlonXP 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 reguarly 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 the RAM, without giving an impression of how faster speeds in this aspect will improve the system as a whole; apart from 'serious tasks' like high-demand databases and scientific computing, memory is not usually much of a bottleneck. 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
Overclocking is sometimes used by commercial system builders or component resellers to sell items at higher profit margins. By buying lower-value components, overclocking them, and selling on as higher value ones, the retailer is able to make a greater profit. 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 there is a risk of shortened component lifespan, the customer should at least be allowed the informed choice to use overclocked components or not.
In some cases the overclocking is seen as a legitimate service, in which the retailer 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.
Of course, manufacturers would rather users seeking high performance pay the premium for their high-end products, but also fear that less reliable components and shortened life span could damage their 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, a claim which often meets a mixed reception.
Advantages with overclocking
- You can, in many cases, purchase a slower processor for a cheaper price and overclock it to the speed of a more expensive processor.
- Faster performance in games and applications for "free".
- Overclocking can be an engaging hobby in itself and supports several dedicated online communities such as those listed below.
Disadvantages with overclocking
- Increasing the clock speed and/or voltage of a component can shorten its lifespan or 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 (but not completely removed) 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 is for many processes, overclocking will bring 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. In video gaming, for example, most people would not 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 little more than computer 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 a problematic amount of heat.
- Powerful fans create a lot of noise, which may make them unsuitable for desktop use. Quiet overclocking can be difficult, although specialised products are avaliable. Generally it is possible to make a component quieter or faster, but both is a considerable challenge. Some people do not mind the noise that extra fans produce, and it is common for overclockers to have computers that are much louder than stock machines. In HTPC situations noise is critical, and as such overclocking is probabaly not advisable.
- Overclocking will not necessarily save money. Often a non-trivial speed increase requires premium cooling equipment, and once the hobby bites it can become an expensive pastime. Most people who consider themselves overclockers spend significently 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 ). 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 already high-end equipment.
- Overclocking usually results in the voiding of hardware manufacturer's warranties.
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 and more advanced and with inexpensive microprocessors being produced with the same core circuitry as faster microprocessors of the same series, a large number of do-it-yourself computer builders overclock to some extent.
Some web sites that provide information on overclocking or serve as a community for overclockers include:
These are online databases that hold detailed information of overclocked systems:
Discuss overclocking, modding and benchmarking at the following forums: