Overclocking, quite simply, is running a piece of computer equipment at a speed above that originally intended by the manufacturer. It can apply to a number of different components, though CPU overclocking is normally the most common. Video cards can also be overclocked, as can motherboard chipsets and memory.
Why Can We Overclock?
All computer equipment has to have certain built-in tolerances so it still works properly in a variety of environmental conditions. CPUs, for instance, have to be able to run without errors whether they're sweltering away in a Cairo office in the middle of summer or in a shed in Reykjavik. As well as external environments, the CPUs also have to be able to accommodate computer manufacturers who skimp on proper cooling, or install them in ultra low-profile cases. For this reason, when you buy a CPU it normally has a fair amount of extra performance potential locked away that you can exploit if you have good cooling equipment.
All electronic circuits have to discharge the heat generated by the movement of electrons. As the clock frequency increases, the amount of heat generated also goes up. This is fundamentally why a chip running at a higher clock speed generates more heat than one running at a slower pace. While you can still overclock using the basic heat sink and fan assembly bundled with the CPU, if you're looking to maximise your overclock, a high performance third-party model is always a better bet.
The speed of a CPU is governed by two factors - the processors' multiplier and the speed of the FSB [or in the case of AMD chips, the HyperTransport bus. The way things work with AMD chips is a little more complicated, as the hyper transport has a core clock and multiplier of its own, so we'll stick to Intel chips for our clock speed examples. Despite this, the principles involved in the overclocking of an AMD processor are much the same. The CPU still runs at a multiple of the HyperTransport core clock; you just have an extra setting to bear in mind when using this hardware. On to the basics.
With current Core 2 Duo CPUs there are three FSB speeds depending on your choice of processor: 200MHz, 266MHz and in the latest models, 333MHz. Intel marketing blurb tells us these speeds are quad pumped by the FSB architecture, so you may also see them labelled as 800MHz, 1066MHz and 1333MHz products respectively. When looking at overclocking, the actual MHz speed is more helpful to us.
Different chips use different multipliers to achieve their designated stock speed. Let us take a 200MHz FSB chip first of all - the Pentium E2160. This chip has a stock speed of 1.8GHz, and therefore uses a multiplier of 9. 200 x 9 = 1800MHz. Finding out your chip's multiplier is extremely easy. Take its stock speed and divide that by its stock FSB. Thus for a 2.4GHz E6600 Core 2 Duo we perform the following calculation: 2400MHz/266MHz FSB = a multiplier of 9.
The above two examples demonstrate how the speed of the FSB affects the performance of the processor. Both chips use a multiplier of 9, but because they have different FSBs, the resulting clock speed is different.
It’s therefore logical and correct to see that you can increase the clock speed of a processor by either changing the FSB, or by increasing the multiplier. Most new motherboards support all three FSB clock speeds right out of the box, so if we could somehow force the motherboard into 266MHz FSB mode while using the Pentium E2160, we would achieve the same clock speed as the much more expensive E6600. As most motherboards grant you manual control of the FSB speed, this is the method by which we can achieve the clock speeds of far more expensive CPUs from budget models.
Naturally, CPU manufacturers are not as keen for you to overclock: after all it would be a lot better for Intel's bottom line for everyone who needs maximum CPU performance to buy its flagship Core 2 Extreme processors for the best part of £700 rather than buying one that costs a quarter as much and obtaining identical or better performance through overclocking. Both Intel and AMD therefore make it more difficult to overclock for us by locking the multiplier on all but their flagship models. Overclocking the FSB also changes the speed of other buses on the motherboard, including the speed at which the PCI-Express, PCI and memory subsystems operate. This makes FSB overclocking more complicated than upping the multiplier as we could in the good old days, but motherboard manufacturers now supply us with a plethora of options to get around or minimise the impact FSB overclocking has on other parts of the PC that respond less well to running outside of the specification. Not all machines can be overclocked. If your PC has an extremely low-end motherboard, or was purchased from one of the big OEM box builders such as Dell, HP, Packard Bell or similar, the manufacturers will have purposely disabled you from being able to delve into the settings and change the FSB and other settings. This is quite simply because they don't want the support headache of dealing with customers who push the machines too far and end up with a 10kg paperweight. This brings us swiftly on to a point that many novice overclockers worry about- what are the dangers of overclocking?
The Risks of Overclocking?
In order to understand the potential risks, we need to look at how CPUs actually work. A processor conducts electricity within it through a series of transistors to perform various functions. Electrical activity generates heat, and heat assists the breakdown of metal. Since transistors use metal gates, too much heat can be dangerous to them. If you increase the speed at which the chip works, you generate more heat, which will break down the chip more quickly. Processors are subject to a phenomenon called electromigration, which is the process of energised electrons breaking down Lines between the transistors. Eventually, the metal lines will be eroded to a degree that they no longer serve as an effective barrier and current 'leaks' into an adjoining line, causing an error [a binary 0 being read as a 1 or vice versa. When we increase the speed or voltage of a given component. The electrons are more energetic and therefore break down the component more quickly.
While this sounds rather scary, electromigration is happening in your PC right now even while it runs at stock speed. The phenomenon guarantees that all CPUs will eventually fait, ifs just a question of how Long that will take. A modern well-cooled CPU might last in excess of twenty years before electromigration takes enough of a toll on the chip to render it unusable, or it might pack in after just ten or fifteen.
A moderately overclocked chip might hasten this demise by five years or so, but in the grand scheme of things the PC will still be obsolete long before any reduction in lifespan accomplished through overclocking becomes relevant. If you push your chip to the absolute bleeding edge, then of course you could hasten its demise rather more quickly. But so long as you use some common sense while overclocking, you shouldn't really have to worry about such an extreme situation arising.
Sometimes you may hear people who don't advocate overclocking, talking about ‘burning out’ CPUs or 'blowing them up'. In reality, this is pure fantasy, and while setting a motherboard to a ludicrously high speed could render it inert, you would have to be fabulously unlucky to toast a modern CPU in this manner. Graphics cards are rather easier to damage while overclocking, as they usually don't have the same temperature-based cut-off that prevents damage, but so long as you take things easy and back down the speed at the first sign of visible artefacting, once again you would have to be tremendously unlucky to cause any permanent damage.
The bottom line is that there is little to dissuade you from overclocking so long as you use common sense. Don't push for too much without the proper knowledge and fully inform yourself as to the intricacies of your particular hardware combination before proceeding.
Beginners Overclocking: CPU’s
If you really don't want to get involved with the nitty gritty of 'proper' overclocking, there are a number of motherboard manufacturers that now offer simplified overclocking profiles designed with beginners in mind. What these do is overclock the FSB by a certain degree, changing other settings such as memory and PCI frequencies as required to keep things stable. The gains you receive with such a method are normally modest at best, but it does allow you bragging rights that you have an 'overclocked machine'.
Some manufacturers take this even further and bundle it up in a convenient Windows-based interface meaning you do not even have to leave to comfort of your desktop to boost performance. Many of these programs allow you to make some reasonably hefty clock speed increases, but don't provide access to other options that would enable these clock speed increases to actually work as intended such as memory ratios and latency timings. Therefore, activating the highest setting on such a program will normally hang the machine, requiring you to reboot. The bottom line is that you will have to delve into the scary world of BIOS tweaking and terminologies to get the best performance out of your equipment, regardless of how incredible motherboard manufacturers' marketing departments claim the bundled software is.
Nevertheless, we took a look at the options available in Asus AI Booster - one of the more common programs you're likely to encounter if using an enthusiast PC. Similar programs exist from other manufacturers in the form of uGuru from Abit and DOT (Dynamic Overclocking Technology] from MSI, which are also great options for overclockers.
The Booster applications shows useful information such as the fan speed, CPU temperature and the current CPU Core voltage, Other options appear when you click the settings spanner icon, including options to bump up the CPU external frequency [within limits] and make simple adjustments to voltages.
Regardless of how you overclock, the first thing you need to do is check for stability. It's extremely unwise to test stability of any overclocked machine with your main OS install, because if things go pear-shaped and you generate enough errors, you can permanently corrupt important things like the boot.ini files and registry, some of which require a repair installation or even a format to fix. The period of time after you've backed everything up and are prepping for a complete format and reinstall which Windows typically seems to need once a year or so) is the perfect time for overclocking fun, because if you corrupt anything, it isn't a huge deal.
The prerequisites for testing the stability of an overclocked machine is something that not only stresses the components, but also reports back on any instability !calculation errors) found. Heating the system up and waiting for a crash is not a good way to test!
One of the best programs for testing overclocking stability is Prime 95, which calculates prime numbers to many decimal places and compares them to a base record known to be correct. CPU calculation errors manifest themselves as rounding errors, which halts the test and tells you the CPU has failed. Prime 95 has been bundled up as a second program optimised for multi-core processors called Orthos and can be down loaded free of charge from sp2004.fre3.com/beta/beta2.htm. This program allows you to select the test type and run the torture test for as long as you choose. Major errors usually manifest themselves within the first twenty minutes or so, so if you're overclocking incrementally and want to see how stable it is at each stage, after twenty minutes of stability, it is reasonable to tick the speed off as stable and try for the next incremental increase. When you finally hit the speed you're shooting for, you should soak test the machine overnight to guarantee it will not flake and let you down when doing critical work.
If you take the overclock too far; Orthos will manifest this as an error and will halt the test. Occasionally, the system may hang instead of erroring, either way, as a beginner overclocker, the only option is to back the system down to a more stable speed. There are various ways of increasing the stability of the machine to get higher clock speeds stable, and these are covered in our advanced section.
Beginners’ VGA Overclocking
Video cards, like motherboards, occasionally come with manufacturer-supported overclocking applications that allow you to squeeze out some extra performance without pushing the envelope too far beyond what is sensible. An example is the DOT Express application from MSI. This allows you to increase the core and memory clocks on its video cards, though not far enough to cause any permanent damage. Overclocking software also comes as an optional extra in NVidia's driver control panel application in the form of nTune, which also enables core and memory clock alterations, plus the option to overclock your motherboard from within Windows without too much effort if it features NVidia chipset. AMD also allows you to overclock your Radeon cards from within Windows with a tweaker built into the Catalyst Control Centre, though this is far more restrictive than the NVidia alternative. While clock speed increases are always nice, you will get a lot more flexibility if you move away from manufacturer supported applications and load up a third-party application such as RivaTuner or ATITrayTools, both of which are freely downloadable, but are not really suitable for beginners.
Overclocking video cards is as simple as increasing the values on the sliders for the core and memory frequency and hitting apply, the settings will then normally be tested in 2D mode for a short period (which is almost worthless) and you then have the option of confirming the speed changes. If you're choosing to manually overclock rather than using pre-defined overclocking profiles as found in many manufacturer-provided software applications, we would suggest increasing your core clocks and memory clocks separately
First of all, increase your core clock speed by 10MHz, and then run loops of an intensive benchmark such as 3DMark 2006, If all is well, increase it by another 10MHz and repeat the stability test. After increasing by 20MHz, it's not wise to continue increasing by such a large increment, though this varies from card to card. 5MHz increments are more sensible, testing once again after each increase. As soon as you start to see distortions, which are usually manifested as either errors in the polygons or as a speckling effect over the screen, immediately exit the benchmark and reduce the core back down to its previous stable setting.
Once you've determined the maximum core clock, reset it to standard and repeat the process, this time increasing only the memory clock speed. Once you have your optimal speeds for both core and memory, combine the two to get your maximum theoretical overclock. You may find that your maximum speeds on both sliders will have to be reduced slightly for 100% stability, as more power is required to overclock both the memory and GPU at the same time. When you think you've found the sweet spot, continue to bench test for several hours to rule out any errors that may only creep in after extended periods of play.
If you push your graphics card too far, as with any kind of overclocking, you can run into problems. Push too far and you'll typically see errors in the geometry, or annoying speckling effects on the screen. Push the memory too far, and you usually see flashing polygons or textures where the graphics are not being outputted correctly. Just as a CPU overclocked too far will make mistakes when executing programs (often causing a crash!. a graphics card also makes calculation mistakes which are manifested as visible distortions. Sometimes distortions will appear even after you take the speeds back down to settings they were previously okay at. If this is the case, power down the system for a few minutes to reduce temperatures, and then load it back up and retest at the previous settings.
Intermediate/Advanced Overclocking: CPU
The learning curve when moving from the Windows-based tweaking applications to hardcore BIOS overclocking is quite a steep one, but the gains in performance more than justify the effort you will need to initially put in. Press Delete to enter the BIOS when you switch your PC on (assuming your PC requires Del to do this) and proceed to the relevant area where the tweaking options are stored. This differs depending on the model you have, but will normally be found either in a specific overclocking area (as found in Abit and DFI boards) or in a more general 'Advanced Settings' area as found with many others including MSI, Gigabyte and Asus. We've used the latter in our examples, as Asus is the most popular enthusiast brand.
AI Tuning in the Asus BIOS can be set to auto, predefined defaults which are similar to the overclock profiles you found in the software overclocking utilities discussed earlier, or manual which will reveal all of the juicy tweaking options you need to unlock to maximise your performance.
Before we proceed we should take a look at some of the terms you are going to need to be familiar with before you can tackle this kind of overclock:
FSB/Internal CPU Frequency/CPU Clock
The motherboard's internal CPU frequency or FSB is called many different things by the various manufacturers. So you'll have to refer to your manual to find out what your chosen brand calls it. Regardless, this is the value you change in order to increase the FSB speed and therefore the speed of the CPU. Higher FSB speeds also open up bottlenecks in bandwidth and memory performance, so the gains of a faster FSB go beyond the resulting CPU speed increase alone. For this reason, sensible overclockers will occasionally sacrifice absolute CPU speed in favour of a faster FSB speed. The default option for this value will be dependent on your CPU, but for a modern Intel chip will be 200, 266 or 333MHz. All good tweaking boards offer incremental increases rather than large sweeping changes that allow you to really fine-tune the speed of the system.
Memory Divider/Ratio/Speed
Once again, this setting varies hugely in how ifs displayed on various boards. It can either be shown as a ratio, or more helpfully as memory speed itself on most of the better overclocking boards. The memory speed increases linearly with the FSB, so if you increase an FSB of 200 to 220, the memory will also increase in speed by 10%. Fortunately, motherboard manufacturers recognise that not all of us can afford PC-100000000 memory which allows for limitless ceilings, and allows you to change the ratio that the memory operates at in relation to the FSB.
CPU Voltage
CPU voltage is another option you need to become familiar with tweaking if you want to get the best out of your chip. Before you start to change the voltage, you should be aware of the stock voltage of your processor and not increase it too far beyond that value. For Core 2-based processors, the voltage is dynamically adjusted depending on load. but sits around the 1.3-1.35V range. If using the stock cooler, we would not recommend going beyond 1.45V, and even if using something more exotic, not beyond 1.5V for long term use. Athlon 64 voltages depend on the core revision used, but this information is easily found online or using CPU-Z (www. cpuid.com).
Memory Voltage
When overclocking the FSB, memory speeds increase regardless of what ratio setting you select. Memory often needs more voltage when running at the highest speeds, and you should check the maximum supported voltage supported by your manufacturer. Corsair, OCZ, Mushkin and other big players all publish their recommended voltage range for all of the memory products they sell. Do not always assume that more voltage is always more stable when adjusting these settings.
PCI-Express Frequency
The PCI-Express bus also increases linearly with the FSB. It is, however, much better to lock this setting to 100MHz - the recommended bus speed. Pretty much all modern overclocking friendly motherboards allow this to be a fixed frequency. Some minor performance boosts can be had from a faster PCI-E bus, but the ends usually do not justify the means when it comes to stability.
PCI Clock Frequency
As exactly with the PCI-Express bus, the PCI bus is a function of the FSB and increases linearly. Likewise, it can be locked to a fixed frequency of 33MHz - which is the speed you should always lock it to when overclocking. Out-of-spec PCI frequency can cause havoc with add-on cards such as storage controllers and sound cards, and can even cause hard drive data corruption, so be careful to lock this setting.
Memory Timings
Memory timings can either be selected manually, or can be set to 'by SPO'. The SPO is a small chip on all memory modules that tells the motherboard the correct timings as recommended by the manufacturer. The trouble is, these SPO timings are often either not ideal for maximum performance, or may be too aggressive once you increase the memory speed close to or beyond its rated speed. Manual mode is therefore better, which gives you control over the most commonly adjusted timings. If you're unsure about what the timings refer to (for example, options other than the setting of the most commonly adjusted timings) leave the option set to auto.
Now you're equipped with what settings we'll be looking at, enter the BIOS, fix the PCI-Express and PCI frequencies on the board and set the memory timings and speed to their least aggressive settings. For memory, 5-5-5-15 timings are usually sensible, because if you drop them to even slacker timings you can cause a failure to POST due to incompatibility with these rather obscure timings. When first starting out, you should leave the memory-voltage at the settings recommended by the manufacturer, and leave the CPU voltage at 'auto'. Whereas overclocking video cards is always a fairly incremental affair, with certain processors - especially lower-end Core 2 Duos you can afford to be a little more liberal.
If using, for example an E6320 which has a stock speed of 1.86Hz and a multiplier of 7, you can be pretty much assured that it will do 2.33 by setting the FSB to 333MHz at stock voltage; likewise for something higher-end like an E6700 which starts at 2.66GHz and has a multiplier of 10. We have yet to see an E6700-based machine that didn't overclock to 3.0GHz at least. This simply involves an increase of the FSB to 300MHz. Once you've got to what you consider to be the 'safe' increase for your chip (which you should be sensible with rather than overconfident) you can start increasing by increments of initially around 100MHz. At each increment run Orthos for around twenty minutes, and if no errors creep in, try the next increment. After a while you'll undoubtedly encounter errors from your chip.
At this point, you can have a fair idea of how good your chip is. If, for example, you have managed to get your E6320 up to around 2.8GHz without a voltage bump, you're doing extremely well. With a small amount of extra CPU voltage, however, you can do even better. Go back to the BIOS and increase the CPU voltage by around 5%. In a. Core 2 Duo, this would be to around the 1.4V mark. Retest at the speed you were previously unstable at and nine times out of ten, you should be stable without any problems. You can now go back to incrementally increasing the FSB, though we would recommend you drop the increments to around 25-50MHz at a time depending on your chip. Once again, after a while you will hit a wall of instability, at which point you can go back to the BIOS and try a touch more voltage. The limits you can safely go up to with a stock cooler or similar is around 1.45V with a Core 2. Beefier third-party coolers or water cooling may well allow you to take it up higher still, but bear in mind temperatures start exponentially, increasing as you raise the voltage. At 1.5V, an E6320 might operate at twice the temperature it was running at while at stock speed, so you should certainly keep an eye on temperatures. Once you've hit your limit, we recommend you back it off an increment or two to take into account any upward shifts in ambient temperature and soak test it over night with Orthos.
Orthos Stress Prime tests both CPU and memory integrity simultaneously, which occasionally makes determining what is causing the problem tricky. Fortunately, there are some tips which make this easier. If it's always the same core that fails, it's more likely to be CPU. If it fails on either CPU 0 or CPU 1, then it's more likely to be caused by memory. Bear in mind that as you reach the upper limit, other factors such as the FSB ceiling of the motherboard and chipset temperature may come into play. At this point, sometimes it's better to admit defeat and back it off to the last most stable speed and accept that you have reached the highest sensible speed.
Intermediate/Advanced Overclocking: Video Card
The next step beyond using the driver-based or manufacturer provided tweaking programs when overclocking the video card is to move on to more advanced packages that afford greater degrees of flexibility with clock speeds and offer other useful features such as automatic artefact scanning and the ability to tinker with advanced rendering options usually only accessible from the registry.
Riva Tuner affords you most of these options for pretty much every contemporary card on the market, and best of all you can create custom fan profiles to suit your level of cooling. While the standard rpm control profile of the NVidia drivers does pretty well for most people, others find the constant changing of fan pitch while playing games distracting and annoying. The RivaTuner profile system allows you to define your own temperature steps at which the fan spins up and slows down, and also has a comprehensive temperature monitoring display pulled directly from sensors on the video card.
Different options will be available on different cards, but if you have something high end or reasonably new, most of these options should be available to you. The latest version of Riva Tuner adds new advanced features such as independent shader clock adjustments in Vista, though these are still quite tricky to get your head around as they behave strangely when interacting with the ROP clock speed. In order to use this feature you also need an 8xxx series card and the very latest NVidia drivers. We may revisit this in more detail in a future video card-specific article, but at the end of the day, the best way of getting the most out of advanced tweakers such as this is to read the relevant support forum (forums.guru3d.com), or just try tweaking various options yourself. You will rarely break anything permanently, or at least nothing that a driver reinstall will not cure.
Extremely Advanced Overclocking
Once you've exhausted the maximum clock speed your CPU or video card is capable of using normal air cooling, you can often increase the performance yet further by installing something more exotic. These options include custom-built Vadim-equipped water coolers, phase change units such as the Vapochill from Asetek and good-old-fashioned liquid nitrogen. While the latter is fun for going for overdocking records, it certainly can't be considered as a usable long-term solution. The Vadim and a properly designed water cooling loop, however, certainly can.
Once you've your exotic cooling set up, you need to find ways of enhancing the capabilities of your motherboard to provide extra CPU or memory voltage, or other modifications that reduce the tendency of modern motherboards to reduce the core voltage under load (commonly called a vDroop mod). As these all differ depending on the technology you're using, it would be pointless to reproduce them in print. Instead post your questions here.
Last edited by Rob on Sun Oct 21, 2007 6:47 pm; edited 3 times in total
Thanks guys for the comments. I can't take the credit for writing this piece, I wish I could but I came across it in one of my computer mags and with a little OCR and proof reading - it's here for all to enjoy.
My hope is that I/we can add to it to give us some good basic pointers in overclocking. Overclocking is such a black art to those who don't understand it I'm sure we could all pick up a point or two from it.
no rush, wait untill our coder finishes what he started and it wont be lonelly anymore in there as The Editor mentioned, in the next few weeks you would see a few changes
So here is one from me 
