How To Assemble A Desktop PC/Overclocking

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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.

Extensive overclocking will result in the destruction of hardware so ensure proper cooling before overclocking.

Overclocking is like souping up a car: if you just want to get where you're going, there's no need for it. But it is fun and educational and can get you a machine that provides performance all out of proportion to its cost.

Think of the 3GHz on your new 3GHz Pentium 4 as a speed limit asking to be broken. Some other components in your computer can also be overclocked, including RAM and your video card in many cases. Over clocking is possible because of the way electronic parts, especially VLSI (Very Large Scale Integration) chips are made and sold. All processors in a given line, the Pentium 4 for example, are made the same way, on a large die that is cut up into individual processors, those processors are then tested and graded as to speed, the best chips will be marked as 3.0 GHz the second best 2.8 etc. As time goes by and production processes and masks improve, even the lower rated chips may be capable of faster speeds, especially if vigorous cooling is implemented. Also many manufacturers will mark chips that test faster at slower speeds if there is higher demand for the lower end component.

It’s important to note that not every chip will be overclockable; it’s really the luck of the draw. Some companies that sell ‘factory overclocked’ systems engage in a practice called “binning” where they buy a number of processors, test them for overclocking potential and throw the ones that don’t overclock in a bin to be resold at their rated speed. Even with processors that have a reputation for overclocking well, some parts simply will not exceed their rating.

That said, effective cooling can give a boost to a chip's overclockability. With luck you will be able to get extra performance out of your components for free. With luck and skill you can get performance that is not possible even when using the top of the line components. Sometimes you can buy cheaper parts, and then OC them to the clock speed of the higher end component, though the cost of extra cooling can compromise any money you may be saving on the part, not to mention warranty and part life issues.


Things that can't be overclocked[edit]

Although it is possible to overclock many of the components of a computer (such as the CPU, FSB frequency and video card), it is not possible to overclock all components. For example, it is not possible to overclock a hard disk drive nor an optical drive such as a CD-ROM drive. For such devices other solutions exist, i.a. use a quicker file system and/or faster components in the first place; also in some special cases of hard disks drives, update the driver (which contains optimized code); remap blocks with high latencies to low latency blocks (using a tool such as mhdd), and in event a RAID is present, change the configuration, driver and/or software and/or settings. However such techniques and procedures are beyond the scope of this document.



Choosing the CPU[edit]

While the CPU is usually the best component to overclock , most CPU's these days are locked , which means that the multiplier cannot be changed from its default clocks. While previously(until Sandy Bridge) , users used to work around this limitation by adjusting the base clock of the CPU , on Sandy Bridge till Broadwell(2nd to 5th) , attempting to do so over a few megahertz would usually cause the system to crash , even if the CPU itself is stable. This is because increasing the base clock would also affect other system components.

This means that , at a best case scenario of a 5 MHz increase over the usual 100 MHz base clock , an i3-4370(3.8 GHz) can only be overclocked by 38*5 = 190 MHz , which would increase the clock speed to only 3.99 GHz.

This limits your CPU choice to the following , if you want to overclock.

  1. CPU's labelled with a K at the end of their model number(eg:- i5-4690K)
  2. Extreme Edition processors (X series). An example would be the octa-core i7-5960X.
  3. Pentium G3258(more on that later)
  4. C(high end graphics) line.

This also means that you would usually have to pay not only to the tune of an i5(since you can't overclock an i3) , these overclockable chips usually come at a 5-15% premium over the non overclockable but otherwise identical CPU.(There are some exceptions though).

Now about the Pentium G3258. This chip caused a lot of hype when it was first released. This is because it was the cheapest and lowest-end Pentium chip released by Intel in honour of its 20th year anniversary. However , the main steal in this is the fact that this CPU is highly overclockable , which made all the difference. Still though , it won't reach the level of a stock i5 with overclocking , and its dual-core no hyperthreading design can hurt it badly. If you really need to build an ultra-budget PC , then this would most likely be your best choice.

The integrated graphics on the chip can usually be overclocked even on otherwise non-overclockable CPU's.

How to overclock[edit]

For older computers , one changes the clock speed of the CPU in the BIOS. This holds true for newer computers , but you can usually use Intel's Extreme Tuning Utility(XTU) if you want to do it in Windows itself. This method , while probably safer , is not the best method to overclock.

Assuming that you have a multiplier-unlocked CPU , head on to the BIOS , look for a CPU-modifying option within the BIOS(it depends between manufacturers) , and raise the All-Core multiplier by a notch(For example , if you have a 3.5 GHz chip with a multiplier of 35x , raise it to 36x).

Then boot back into Windows and then run a stress tool like Prime95. It is a good idea to run it for some time(like an hour) but not for too long as you may end up damaging your CPU instead. Keep a watchful eye at the CPU temperatures , you should not go over 85C. If you do , you may need a better CPU cooler. Do NOT use the stock cooler if you are overclocking!

If it passes , go back into the BIOS and increase the multiplier again by a notch. If it fails , return back to the BIOS and then raise the CPU voltage slightly. Then repeat the stress test.

Continue this process till

  1. The stress test has failed and you've applied enough voltage , or
  2. The CPU is running too hot.
  3. The CPU is throttling(reducing speeds)

It is important that you do not apply too lunch CPU voltage as you may end up increasing the voltage too far and damage it. Also remember to keep any adaptive voltage settings on , as they reduce the voltage and prolong the life of your CPU when it is in idle.

For older PC's[edit]

Assuming that you have selected a quality motherboard, high-quality RAM , thermal solution and power supply; you may wonder why your processor won't exceed a certain speed limit. Lets assume that you have a memory chip that is capable of taking the maximum frequency the motherboard can throw at it and yet, when you exceed a certain speed limit you realize that your system becomes unstable.

A PCI bus generally runs at 33 Mhz. When you exceed 35-36 Mhz, the hard disk and other IDE devices become unstable, because the IDE controller is controlled through the PCI bus. Oftentimes, you may encounter texture corruption, when your AGP bus exceeds a certain speed limit. This was often observed on older motherboards that wouldn't allow you to lock the AGP and the PCI bus at stock speeds.

The good news: regardless of the FSB speed, most motherboards nowadays automatically ensure that the frequency of the PCI, AGP and other buses always remain constant (in other words; their speeds are locked unless you deliberately change them). This implies that the other components connected to the motherboard don't undergo stress when the FSB speed is raised. You have the fastest RAM you could find and the obscenely fast speed ratings on your ensure that you can extract the most performance by bumping up your FSB speed to the limits.

The main culprit that plays the spoilsport is your CPU. Even if you have an exceptionally good thermal solution, your CPU won't exceed a certain limit.

Example: I had experimented with a Pentium III 700E Mhz processor and a Pentium III 800E MHz processor on an Asus CUBX-E motherboard using Kingston PC-133 SD-RAM. The reason I chose these 2 processors for experimentation was because they both used a FSB speed of 100MHz. This motherboard was really flexible, I was able to increment the FSB to 150Mhz. I was able to extract 1050 MHz from the stock 700Mhz. This is because the multiplier is 7, which unfortunately cannot be changed. So I bumped up the FSB from 100Mhz to 150 Mhz; which gave me the resultant speed of:

× 150
(Front Side Bus)
= 1050 MHz
(resultant frequency)

Simple arithmetic? Yes. Now, logically speaking, if I can extract 1050Mhz from a 700Mhz processor; I should be able to extract 1200Mhz from an 800 MHz processor. This is not true. I tried doing exactly the same with the 800 MHz processor and the Computer crashed. However, it was stable when I set the FSB speed to 133 MHz. When I set the FSB at 133 MHz ; this was the result:

× 133
(Front Side Bus)
= 1064 MHz
(resultant frequency)

This simple experiment shows that a CPU gets saturated after a certain clock speed. Typical symptoms of an erratic CPU include instability and at times, you may not be able to boot up at all.

This particular CPU die was manufactured using a 0.18u process. When Intel launched a similar CPU using a 0.13u process; they shipped those CPUs with the stock speed of up to 1.4Ghz. This CPU core was based on the P6 Architecture and it used a 10 stage pipeline. Presently, Intel manufactures the Pentium-M CPU which is based on the P-6 architecture; the difference being that they manufacture it using a 0.09u process and they have increased the depth of the pipeline.

These terms may seem cryptic and this concept may be difficult for some to grasp. It's really very simple: To be a successful overclocker; you need to purchase the best CPU possible; not necessarily the fastest. Always go for a processor that uses the latest manufacturing process. A CPU rated at 3Ghz which is manufactured by using a 0.13u process won't overclock as well as a CPU that is rated at 2.6Ghz using a 0.09u process.

Deeper pipelines ensure that the CPU has the capability to scale higher in terms of speed. The disadvantage is that a CPU with a deeper pipeline is slower than a CPU that uses a smaller pipeline assuming that they are running at the same speed. AMD Athlon CPUs are famous for their relatively short pipelines. Thats why they perform better than the Pentium 4 CPUs at the same clock speed. Before purchasing the fastest processor, always keep this in mind. Choosing a processor smartly helps you extract the maximum speed out of your machine. You don't need to know what a pipeline exactly does. Refer to the processor spec sheet, find out these basic details of the CPU core and its architecture and choose accordingly.

To increase the computer's stability, you may also disable the spread spectrum; set the PCI speed to 100MHz; set the voltage to the middle range, not too high; and disable any smart fan settings. and those settings work for all recommended boards.

Video card[edit]

Two different parts of a video card may be overclocked[1], the GPU (Graphics Processing Unit) and the RAM. In addition, disabled pipelines on a video card may also be enabled through third-party drivers, third-party software, or direct hardware modifications depending on your video card type. Overclocking a video card is usually done through third-party or proprietary software.

Recent ATI proprietary Catalyst drivers feature an interface called Overdrive that allows for dynamic GPU frequency scaling based on its temperature and load. Increase the load, the clock rate increases for performance, but it's balanced against the increasing temperature. Sufficient for simple increases in overall performance, this doesn't allow for the best performance increase which requires overclocking the memory. For that you'll need third-party applications or drivers.

An application example is ATITool. This program has many options, including GPU and memory overclocking, temperature monitoring, and fan control, allowing for a much more complete solution to overclocking ATI based video cards. There are many third party drivers,, for example hosts ATI and nVidia drivers as well. Both of which include integrated overclocking and many unlocked features, including enhanced image quality for nVidia-based cards.

nVidia video cards can also be OCed through a hidden feature in the driver called coolbits. Coolbits is a feature that can be unlocked by creating a DWORD in regedit for windows operating system. To use the coolbits feature, for windows just simply open the regedit then open the directory HKEY_LOCAL_MACHINE>Software>NVIDIA Corporation>NVTweak and create a new DWORD value in the NVTweak folder named coolbits then right-click it>modify type 3 for single card or 1A for SLI in the value name .It is a good a overclocking tool as it has a fairly conservative "optimal clock" once you have thus increased the core clock (not the memory clock!!) run a gpu intensive task like 3dmark, repeat until you have a sudden drop in the benchmark score. This is the thermal throttling kicking in; do not push it any harder as it will result in permanent damage to your gpu. Back off the clockspeed by about 20-30mhz

The most important thing to remember about overclocking a video card is cooling. This can't be stressed enough. Just as a CPU can be damaged or have a shortened lifespan by overclocking or excessive and prolonged heat, so can a video card. In the past year many inexpensive and easy to install options have surfaced for cooling a video card, from adhesive ram heatsinks which attach to un-cooled ram chips, to rather expensive water-cooling solutions. A good midpoint (both in cost and effectiveness) solution is to purchase and install a direct exhaust, "sandwich" cooling solution. Direct exhaust means all air from the cooling fan is blown across the video card and directly out of the computer case, usually using the open PCI slot below the AGP (or PCIe) slot. This allows for substantially lower GPU temperatures.

A sandwich cooler is two aluminum or copper heatsinks, shape formed for a particular video card, that "sandwiches" the video card in between the two and are usually connected by some kind of copper heat pipe which allows for the hotter side to convey heat to the cooler side for dissipation. The GPU should never surpass 80 degrees Celsius for optimal performance and to avoid damaging the card. Most of the latest video cards are rated to go up to 90c, but this is NOT recommended by anyone. The optimal temperature for a video card is 40-55c for the card itself (the GPU's temperature differs depending on which you have,) but the lower you can get it, the better.

It is also possible to use software to change the fan speed on certain cards. Changing the fan to run at full speed can cool the card better, dependening on your card and the speed of the fan in the first place. Software such as Rivatuner can be used for Nvidia based cards.

One important thing to note. Many think that the option which says "AGP voltage" in their BIOS can be used to "voltmod" a video card to get a bit more power out of it. In fact, it's used for something else, and raising the AGP voltage can and probably will cause damage to a video card.

Getting the few extra MHz out of a chip[edit]


When increasing the speed of any computer components you are making the components work harder and by doing so they output more heat. Heat can cause system instability so cooling is necessary to help keep your components stable at higher speeds. Without good cooling you could harm or shorten the life of your system. CPU temperature can usually be checked from within the BIOS. However, these are inaccurate as your CPU is under almost no load in the bios. SiSoftware Sandra may be used within Windows to check temperature. This should be done when your CPU has been under a heavy load for a while for optimum results.

There are three types of cooling that are generally accepted for overclocking: Air, water, and peltier.

With both air cooling and water cooling some type of transfer material is needed to move the energy away from the sensitive electronics. The device used for this purpose is a heatsink. The two most popular heatsink materials are Aluminum and Copper. The heatsink that is stock on factory computers by major manufacturers (Dell, Gateway, IBM) is usually made of aluminum, which has satisfactory heat transfer characteristics. However when overclocking more heat is being produced from the increase in power consumption. In order to obtain lower temperatures a material with better heat transfer properties is important and copper is the material that offers the best ratio of price/performance.


Chips at higher speeds may need more power. Raising the vcore voltage on a CPU might enable it to go at slightly faster speeds but by doing so you add a lot more heat output from the CPU. The vcore of a processor is the voltage at which a chip is set to run at with the stock speed. This voltage may need to be changed when the multiplier is raised because otherwise the transistors in the chip won't switch fast enough - transistors switch faster the higher the supply voltage. If there is not enough voltage then the chip will begin to make mistakes and give bad data results. Good cooling is needed to keep the system stable at higher speeds. Raising the vcore too much may harm or shorten the life of your system. Raising the vcore can also greatly affect the stability of the system. This is where a high quality PSU will come into play. While many cheap, no-name brand PSU's will crash and die with more vcore, a good quality one will live to serve you for a long time. For most modern Intel and AMD processors, it is strongly recommended not to exceed 1.45V on the vcore, however even 1.45V can significantly reduce the lifetime of a CPU.

Note: increasing the speed (multiplier or fsb) without changing the voltage will also increase heat output, but not as much as when also increasing voltage. Having said that, increasing the multiplier or FSB without adjusting the voltage may make your system unstable (undervolt).


  1. Coles, Olin. "Overclocking the NVIDIA GeForce Video Card". Retrieved 2008-09-05. 

External links[edit]

Choosing and installing the software · Silencing