Basic Concepts of Overclocking Intel Core i3/i5/i7 CPUs

In this article we aim to emphasize on the basic concepts of overclocking the latest Intel Core processors, not matter the generation or model. It's totally recommended to read it before you start playing with BIOS settings, since you must have a well organised plan, like following the next step of an algorithm. Once, you feel comfortable with overclocking fundamentals, then you are able to put theory into practice and then overclock your PC. Pay attention though, that this guide is not intended for notebooks or tablets, but Desktop PC only.

Overclocking means that you are already familiar with your hardware no matter age, studies and engineering background. There are a few basic principles that you need to know before you click "Save changes and Exit" and protect your hardware from damage.


  1. Introduction

  2. Requirements & Disclaimer

  3. Intel Micro-architecture

  4. BIOS Setup

  5. Frequency and Voltage

  6. Identify your VID

  7. Maximize BCLK

  8. Maximize Memory

  9. Stabilize CPU

  10. Nehalem Overclocking

  11. SandyBridge Overclocking

  12. IvyBridge Overclocking

  13. Final Words


The purpose of Overclocking

What everyone needs can be quite controversial to discuss, although the same basic principles apply to all of them. Hence, the basic process it's the same for everyone whether you are planning to use your system as daily PC, gaming rig o just want to run a single benchmark.

Overclock but stable!

Everyone has their individual definitions of a what a stable system means.  It's true that overclocking targets to power users who need lot's of cores and threads to run their applications. So the best way to make sure that your PC won't crash while working on a heavy app, it's to test it under the same conditions - such as running a stressing tool.

For example, if you are a gamer then your PC should be stable enough to play games without crash due to an overclock pushed too far.

For a hardware maniac that benches all night long, he needs to be stable just for 7 seconds to validate its score.

So as you can see, there are different meanings applying into a stable system. Reliability is the key in our guide, thus we don't intent to teach you how to break the next world record, but let you know the basics.


UbuntuXtreme is not responsible for any bad things that might  happen to your PC as a result of you listening to our advices. There will always be a risk that overclocking can damage your hardware, so please we are not responsible for anything. Note, that overclocking will also void your PC warranty.


Sad but true, we cannot cover all the details here. So you need a little bit of BIOS experience before you read this guide.  If you do not, please do not be afraid to get into your BIOS and have a look around. I suppose that most you have already changed the first boot device. Don't ya?


Cooling not only plays a huge roll in reducing temperatures but is also determine how much voltages you can feed to your CPU before you damage or even kill it, especially with the 22nm IvyBridge CPU’s who are much more sensitive to voltages. Electronic components behave differently under extreme cooling than under conventional cooling.

Use voltages in moderation and rather be safe than sorry, especially if you cool with conventional cooling such as air or water.

Time Consuming

Our method can be seriously time consuming, which means you are not going to push your hardware up to 4.5 GHz in 5 minutes. If UNIX had teach us something, is how to do things right. So with that in mind, we will attempt to isolate each portion of the system and overclock one piece at a time. This may seem time consuming at first glance, but rest assured this can potentially save you hours of troubleshooting and frustration.

That been told, please head onwards to the next page :)

First off you need to identify your hardware. Learn everything you can about your system and then search for it in Google. Luckily, there will be others using the same hardware rig, hence googling it's always a nice trick to check upon your system's limits. That's the reason why hardware forums will never die.


The CPU micro-architecture has taken a huge leap from the 65nm Core to the new generation 45 and 32nm (SandyBridge) and 22nm (Ivy Bridge) technology, it has brought many changes not only to the CPU’s but also to the chipset and motherboard design and functioning. This is what makes overclocking the i3/i5/i7 CPU’s so much different to their predecessor LGA 775 CPU’s -- meaning Core2Duo/Quad (65nm).

The naming convention can be a bit confusing so let us look at the various CPU and their names:

[toggle title="Codenames, die size and sockets"]

  • Nehalem - 45 nm die size | 1366 socket

  • Bloomfield - 45nm die size | 1366 socket

  • Lynnfield - 45nm die size | 1156 socket

  • Westmere/Clarkdale: 32nm die size | 1156 socket

  • Westmere/Gulftown: 32nm die size | 1366 socket

  • SandyBridge: 32nm die size | 1155

  • E-SandyBridge: 32nm dize size | 1155/2011

  • IvyBridge: 22nm die size | 1155/2011


First we have the Nehalem family which are all 45 nm CPU’s that included i7 1366 Bloomfield (i7-920 i7-975) and Lynnfield socket 1156 i5/i7 (i7-750 to i7-860). These are all quad cores with HT except for the i5 which has no HT. Then the next family is Westmere which is essentially die shrink 32 nm CPU version of Nehalem and again you have the Clarkdale (socket 1156) in flavors of i5 and i3, both dual core processors with HT. Gulftown which is the hex-core CPU’s and not available yet are also part of the Westmere family and features 6 physical cores with HT and will be socket 1366 only. Last year we had the SandyBridgefamily which are all 32nm CPUs included all i-X families.

With Sandy Bridge, Intel has tied the speed of every bus (USB, SATA, PCI, PCI-E, CPU cores, Uncore, memory etc.) to a single internal clock generator issuing the basic 100 MHz Base Clock(BClk).With CPUs being multiplier locked, the only way to overclock is to increase the BClk, which can only be raised up to 5-7% without other hardware components failing. As a work around, Intel made available K/X-series processors which feature unlocked multipliers; multiplier cap of 57 for Sandy Bridge. For example during IDF 2010, Intel demonstrated an unknown Sandy Bridge CPU running stably overclocked at 4.9 GHz on air cooling

After 6 months, E-SandyBridge have launched and there is alternative method known as the BClk ratio overclock. Nowadays we are happy to see the new 22nm Ivy Bridge family.

So, to summarize, we have socket LGA 1366, LGA1156, LGA1155 and LGA2011 which are essentially the board platforms that carry certain 45 and 32 nm and 22nm CPU variants. Both platforms are DDR3 where the 1156 and 1155 are dual channel only.

Intel Core i3, i5, and i7 CPU’s

The following are the different CPU’s available today on the market, except for the Gulftown hex cores which will be available late 3rd quarter of 2009.

[tabs tab1="i3 530, 540" tab2="i3 2120, 2100" tab3="i3 3220, 3225, 3240"]

[tab]Core i3 (Clarkdale – i3 530, 540) - First Generation

The least expensive and least powerful choice are the Core i3 chips. These are currently limited to two physical cores with both the i3 530/540 models supporting Intel® Hyper-Threading Technology. At this time, all i3 CPUs have two pieces of silicon (or dies) in the CPU. One contains the actual processing cores and all of the L1, L2, and L3 caches. The second die contains a GPU (graphic processing unit) which is capable of outputting video without the use of a dedicated video card when used with an H55 or H57 based motherboard. This second die also contains the PCIe controller and the dual channel IMC (Integrated Memory Controller). The first die is manufactured on a 32nm process, the second die is manufactured on a 45nm process. The two die are linked with the Intel QPI (Quick Path Interface). All Clarkdale i3 CPUs work only on LGA1156 based motherboards -- quite obsolete and hard to find these days.

[tab]Core i3 (SandyBridge-i3 2120, 2100) - Second Generation
The entry level of SandyBridge CPUs -- 32nm -- are identical to low end systems with embedded GPU (using HD3000/2500). They have 2 cores with HyperThreading, based on motherboards with LGA 1155 socket. Also there is dual channel IMC built inside the CPU and it has 3MB L3 cache.


[tab]Core i3 (Ivy Bridge -i3 3220, 3225, 3240) - Third Generation

The entry level of Ivy Bridge CPUs -- 22nm -- are identical to low end systems with embedded GPU (using HD4000/2500). They have 2 cores with HyperThreading, based on motherboards with LGA 1155 socket.




[tabs tab1="i5 650, 660, 661, 670" tab2="i5 750" tab3="i5 2500K" tab4="i5 3450, 3330, 3470, 3570, 3550"]

[tab]Core i5 (Clarkdale - i5 650, 660, 661, 670) - First Gen

Dual core i5 CPUs (Clarkdale) are identical to the i3 CPUs, but also include Intel® Turbo Boost Technology. All Clarkdale i5 CPUs work only in LGA1156 based motherboards.[/tab]

[tab]Core i5 (Lynnfield – 750) - First Gen

The most powerful Core i5 of First Gen; Quad core i5 CPUs (Lynnfield) are identical to the low end i7 CPUs, the only exceptions being their lack of Intel® Hyper-Threading Technology, Intel® Virtualization Technology for Directed I/O (Intel® VT-d) and Intel® Trusted Execution Technology (Intel® TXT). All Lynnfield i5 CPUs work only in LGA1156 based motherboards.

[tab]Core i5 (Sandy Bridge - i5 2500K) - Second Gen

The high end Sandy Bridge processor that rocks with 4 core CPU's made for LGA 1155 based motherboard. These CPU are manufactured on the 32nm process. They have dual channel IMC's built into the CPU die. The PCIe controller is not part of the CPU, but is build into the chipset (on the motherboard), the CPU and chipset are linked with a Ring Technology, outperforming the QPI. There is no HyperThreading.


[tab]Core i5 (Ivy Bridge -i5 3450, 3330, 3470, 3570, 3550) - Third Gen

The mid range Core i5 (Ivy Bridge) are quad core CPUs made for LGA 1155 base motherboards. These CPUs are manufactured on the 22nm process. They have dual channel IMCs built into the CPU die. The PCIe controller supported 3.0 x16 lanes boosting the GPU performance even more that previous generation. They come with 6MB L3 cache while running at frequency range of 3.0 to 3.4 GHz. There is no HyperThreading.[/tab]


[tabs tab1=" i7 860, 870" tab2="i7 920, 940, 960, 965/975" tab3="i7 980x" tab4="i7 2600K, 2700K" tab5=" i7 3930K" tab5="i7 3770K" tab6="i7 3960X"]

[tab]Core i7 (Lynnfield – i7 860, 870) - obsolete

The low end Core i7 (Lynnfield) are quad core CPUs made for LGA1156 based motherboards. These CPUs are manufactured on the 45nm process. They have dual channel IMCs and PCIe controllers built into the CPU die. All i7 CPUs include Intel® Hyper-Threading Technology and Intel® Turbo Boost Technology. Lynnfield based CPUs are unique in that they do not have a QPI. Because the PCIe and memory controllers are both integrated on the CPU die, there is no need for the QPI. They are known to have incredible IMCs and are capable of sustaining extreme memory bandwidth.

[tab]Core i7 (Bloomfield – i7 920, 940, 960, 965/975) - obsolete but still rocks

The mid range Core i7 (Nehalem) are quad core CPUs made for LGA1366 based motherboards. These CPUs are manufactured on the 45nm process. They have triple-channel IMCs built into the CPU die. The PCIe controller is not part of the CPU, but is built into the chipset (on the motherboard), the CPU and chipset are linked with a QPI. All i7 CPUs include Intel® Hyper-Threading Technology and Intel® Turbo Boost Technology.

[tab]Core i7 (Gulftown – i7 980x)

The high end Core i7 (Gulftown) are hex (six) core CPUs made for LGA1366 based motherboards. These CPUs are manufactured on the 32nm process. They have triple channel IMCs built into the CPU die. The PCIe controller is not part of the CPU, but is built into the chipset (on the motherboard), the CPU and chipset are linked with a QPI. All i7 CPUs include Intel® Hyper-Threading Technology and Intel® Turbo Boost Technology. Please understand that these new 32nm CPUs are more sensitive to high voltages, and have been known to fail even when core temperatures are well within “safe” limits.


[tab]Core i7 (Sandy Bridge - i7 2600K, 2700K)

The best edition of 2500K including HyperThreading -- so 4 cores and 8 threads. Please note the the "K" means unlocked for overclocking. So if you have 2600 instead of 2600K, sorry but you cannot overclock. Note the "K" in the end of the part, meaning this CPU is unlocked ready to be overclocked. If you have the same CPU but without the "K", sorry you cannot overclock.[/tab]

[tab]Core i7 (E-SandyBridge - i7 3930K)

The high end E-Sandy Bridge are 4/6 core with HT, made for LGA 2011 based motherboards (preferably using the X79 platform). The processor runs at 3.2GHz (max turbo 3.8GHz) while is fully equipped with 12MB L3 Cache. Note the "K" in the end of the part, meaning this CPU is unlocked ready to be overclocked. If you have the same CPU but without the "K", sorry you cannot overclock.[/tab]

[tab]Core i7 (Ivy Bridge -i7 3770K)

The high end of Ivy Bridge platform is released in September 2012 made for LGA 1155 based motherboards. These CPUs are manufactured on the 22nm process. They have dual channel IMC's build into the CPU die. The PCIe controller is version 3.0x16 lanes boosting your GPU performance even more. The CPU runs at 3.5GHz and has 8mb L3 cache. Note the "K" in the end of the part, meaning this CPU is unlocked ready to be overclocked. If you have the same CPU but without the "K", sorry you cannot overclock.[/tab]

[tab]Core i7 (E-SandyBridge -i7 3960X)

The beast of Intel that rocks with 6 cores and 12 threads running each core at 3.3GHz while 3.9GHz when Turbo is enabled. The model is supported by 2011 socket LGA motherboards. Finally, it uses 15MB L3 cache. The "X" means eXtreme edition.[/tab]


The smaller the die size, the less power it needs. Thus 22nm CPUs are less power-hungry than 65nm CPUs. Bare in mind that modern processors bring inside them an embedded GPU, which makes things even harder to overclock. The IMC is not that good as it used to be, so many overclockers tend to have their RAM frequency at lower levels.


Restore BIOS defaults

To start off, it's very  crucial to understand that you should eliminate any "green environmental" behavior of your motherboard along with any auto-adjusting features. Simply put, we are going to push hardware up to its limits, meaning that overclocking and low power consumption can't live together under the same chassis. Similar technologies that dynamically adjust your CPU frequency (like Turbo Boost) should be equally disabled; because we need to have the full control of our computer, instead of automatically adjusting itself on demand.

It's crucial to disable all these auto configuration settings; if you don't then it'll be much harder to identify what's the faulty parameter in case of instability or failure.

That has been told, get into the BIOS and load optimized defaults. Please disable spread spectrum settings, EIST, Turbo Mode, C1 and lock your PCI frequency to 100MHz and enable LLC (Load-line Calibration). Save and Exit from BIOS.

Although it's not necessary but recommended to turn off  any start-up slash screens, so that you can view your system’s post behavior. Also, feel free to disable any “integrated peripherals” that will not be used (i.e. NICs, extra PATA/SATA controllers, legacy devices, blah blah etc).

If your motherboard fails to post after changing certain settings, you will have to locate and reset the CMOS. Resetting the CMOS restores the BIOS to its factory settings and is a “hard” reset of these settings. Please read your motherboard's manual and familiarize yourself with Clear CMOS jumper -- you're going to need this most likely in case of overclocking failure to restore hard-reset settings.

Understanding CPU frequency

Before we go into how we overclock these CPU’s let us look at what determines how fast your CPU will run. The following simple equation determines the clock speed of the CPU’s cores:

[highlight color="yellow"]CPU Frequency = Base Clocks x Multiplier[/highlight]

This is a biggest change from the old LGA 775 where FSB and multiplier determined the CPU speed. The base clock is similar to the FSB but also has some key differences. The base clock, also commonly spelled bclocks or bclk in forms, is the foundation around all the other frequencies discussed below.

The CPU speed of the new generation is not the only factor that determines how fast your PC will run, we have a few more definitions such as:

[tabs tab1="QPI Frequency" tab2="Uncore frequency" tab3="Multiplier and Turbo"]

[tab]QPI Frequency – QPI or Quick Path interconnect is the Intel communication path upgrade from the older chipset and front side bus (FSB) communication path, so instead of the CPU communicating with the memory via the LGA 775 Northbridge, there is now a direct link (QPI) that increases efficiency. QPI speeds are a function of base clocks, so as you increase your base clock your QPI speed will also increase, yielding an increase in not only communications speeds but also bandwidth, which leads to an increase in PC performance.[/tab]
[tab]Uncore frequency – This sets the frequency of the on-die memory controller and the L3 cache. Like CPU clock speed, dram speed, and QPI frequency, uncore is a multiple of Bclk. Uncore can be set independently of those other frequencies, subject to certain stability limitations. The uncore must be at least 2:1 of the DRAM speed otherwise you will not get a stable overclock, in fact your PC will not even boot if the ratio is not honored. Increasing the uncore:dram ratio above 2:1 yields significant performance gains. However, when the ratio reaches 3:1 it is not possible to maintain full stability.[/tab]
[tab]Multiplier and Turbo – As mentioned above, the multiplier is the second factor in how CPU core speed is determined. Now, not all CPU’s have the same multiplier, it is dependent on where the CPU is positioned in the price/performance curve of Intel’s range of CPUs. Most of these come with a Turbo multiplier which is available if you enable the Speedstep option under the CPU settings. Care should be taken when using the turbo as you may not be able to see the resultant frequency in the BIOS. For instance, if your default multiplier of your CPU is 20 (i7-920) and you set your baseclock to 200 and you boot up with turbo enabled, you will leave the bios at 20 x 200 = 4 GHz, as soon as you enter your Operating system your turbo kicks in so you end up with 21 x 200 = 4.2 GHz. Now if you also have C-State enabled, one CPU core will actually have access to a 22 multiplier which enable that core to run at 22 x 200 = 4.4 GHz. You set your voltages expecting to run at 4 GHz and you cannot understand why you crashed X enter Ubuntu, well, that is the reason, so take care when using turbo and C-State and adjust voltage to accommodate for the higher multipliers.[/tab]


Important Voltages when Overclocking

There a few important voltages which you will need to manipulate while overclocking, below are the main ones. Every motherboard BIOS differ but all of them have the voltages as set out below.

[tabs tab1="VCore" tab2="QPI voltage/CPU Vtt" tab3="VDIMM/DRAM" tab4="IOH Core" tab5="ICH Core"]

[tab]V-Core – Directly related to the CPU frequency. As you increase the CPU frequency you would need incrementally increase the v-core as well.[/tab]
[tab]QPI voltage/CPU Vtt – Increase in this voltage is necessary from the default as you increase your RAM speed, tighten the timings or increase QPI frequency. It also helps to stabilize your overclock at higher base clocks.[/tab]
[tab]VDIMM/DRAM – This is directly related to your RAM memory modules and increase will assist in stabilizing increase in Ram speeds. Care should be taken not to increase this voltage more that 0.5 volts above your Vtt as you could cause permanent damage to your CPU.[/tab]

[tab]IOH Core Voltage- This voltage aids when increasing base clocks above say 200. In most cases leaving it at auto works best.[/tab]

[tab]ICH Core Voltage- This voltage feeds the chip that regulates the communication from the peripherals to the CPU via the DMI. It is best to set this at auto.[/tab]


Now that we have covered all the basics let us jump to what this article is all about…overclocking

Identify your CPU's VID Voltage

Then log back in to Ubuntu and stress your system for 5 minutes using MPrime blend mode; WARNING: Do NOT use IBT or Lynpack methods. At least we personally try to keep avoiding excessive stressing tools. While you'll have been stressing with MPrime, please open our Xray monitoring script and observe the Vcore behaviour. This, my friends, is your actual stock Vcore ( aka VID ).

Test default settings

Go back into BIOS and set your Vcore to VID's value. Then stress your system for a couple of hours (8 to 24 hours) just to make sure that you are stable at stock settings. If during testing you don't notice anything unusual, such as artifacts, instant restart etc, it means your system's rock stable and ready to be overclocked.

Start overclocking

Congratulations! Now your system is under your full control, since there is no any auto-adjust feature enable in BIOS, but only your manual settings. To start off with overclocking procedure, please understand that different approach applies in different platforms, meaning you have to identify first your processor's generation. If can't do this, it's recommended to check your motherboard's LGA socket, and thus identify your CPU's generation indirectly. Please select your processor's generation below:

  1. Generation (2008 models) - Nehalem architecture | 1156/1366 socket

  2. Generation (2010 models) - E/SandyBridge architecture | 2011/1155 socket

  3. Generation (2012 models) - Ivy Bridge architecture | 2011/1155 socket

Maximize Bclock Frequency

The first step to our overclocking scenario starts here, finding the maximum BCLK. For now, it’s only important to isolate it as a variable from our overclocking process. So, assuming your goal is 200MHz bclock frequency, which is a 50% overclock of the bclock frequency, you need to lower the set iGPU frequency to prevent its overclock during this process. If the stock iGPU clock speed is 900MHz and we were to overclock it 50%, that would yield a 1350MHz actual iGPU frequency. To bring 1350MHz back down to 900MHz we would need to reduce it by 33%. So reduce the set iGPU frequency by 33% to 600MHz, with our stock bclock frequency, the actual iGPU frequency would also be 600MHz. However, if you successfully reach your target 50% increase in bclock, your set iGPU frequency will yield an actual iGPU frequency of 900MHz, which is the iGPU’s stock speed.

[toggle title="Isolate the bclock from the CPU"]First you need to isolate the bclock and find its stable limit with your chosen cooling. In order to isolate the bclock from the other components, the first thing you need to do is manually force a low multiplier for the CPU. For example; at stock speed, an i5 750 runs on a 133MHz bclock and a x20 multiplier which results in its stock speed of 2660MHz (133×20). Raising the bclock to 200 with the stock x20 multi would result in 4000MHz for the CPU, which you’re not quite ready for yet. If you are shooting for a 200MHz bclock, then a safe choice for now might be a x12 multi, which would result in a CPU speed of 2400MHz if you were successful in reaching your 200MHz target bclock. Doing this isolates the CPU from the bclock so you can focus on only bclock overclocking in this step. In some situations, x12 may not work, this is just an example though, so don’t be afraid to try other low multipliers if x12 doesn’t work.[/toggle]

[toggle title="Isolate the bclock from the memory"]The fastest rated speed for memory on P55 with an i5 750 (for example) is DDR3-1333, which is a clock speed of 667MHz (dual data rate “DDR” doubles the bandwidth to 1333-like speed). Just like the CPU, the memory receives its clock from the bclock via a multiplier, in this case x5 (133×5=667). This is most often expressed in the BIOS as “2:10″. If you were to overclock the bclock to 200MHz as described before, your memory would be running at 1000MHz (DDR3-2000), and beyond the specs of all but the most extreme memory. To isolate the memory from the bclock, lower the memory multiplier to the lowest setting available, most likely 2:6. If you were to reach your goal of 200MHz bclcok frequency, your memory would only be at 600MHz (DDR3-1200) and well within the capability of all but the worst DDR3 on the market.[/toggle]

[toggle title="Isolate the bclock from the iGPU"]Modern CPUs include an iGPU (integrated Graphics Processing Unit). If you are using an H55 or H57 and all the most X79 based motherboard and the iGPU is enabled, please pay close attention to this section. Some early BIOS versions did not allow for iGPU clock speed adjustment, if you do not have this option in your BIOS, please update your BIOS to the most recent version. This platform is still very new and immature, so this information may only be relevant for a short time. However, at this current time, it appears as though the iGPU frequency setting in the BIOS is based on the default bclock frequency. This means that an iGPU frequency that is set at 900MHz in the BIOS, will only actually be 900MHz if the bclock frequency is set to 133MHz, if the bclock frequency was raised by 25% to 166MHz, the actual iGPU frequency would also go up by 25% or 1125MHz. This is a relatively simple concept to understand, except that YOU have to do the calculation, because the BIOS only reports the set frequency, not the actual frequency. What makes things worse at this time is that there is no software monitoring utility that is capable of reading the actual iGPU frequency.[/toggle]

Bclock voltages

For this step, there are only two voltages you should play with; VTT, and IOH. IOH is easy, if you are running a single PCIe card (graphics card), give the IOH 1.3V, if you are running more than one PCIe graphics card, give it 1.35V. VTT is the crucial voltage adjustment for achieving high bclock stability, which is also known as “CPU VTT”, “QPI/VTT”, or “QPI/DRAM”. This is the voltage that is fed to the IMC (Integrated Memory Controller), and also has a major impact in overclocking the bclock. CPU VTT is the crucial voltage adjustment for achieving high bclock stability. Stock values differ depending on platform and CPU, but as a rule of thumb LGA1366 likes a lot, P55 doesn’t need as much.

So, are you ready to start overclocking? After entering your BIOS and lowering the CPU & MEM multipliers, go to the voltages section and raise your IOH to 1.3-1.35V and your CPU VTT to +0.2V. Then restart your machine and go back into the BIOS, if your system fails to post and return to the BIOS, please re-read the last paragraph in the “prerequisites” section above, and start over. If you still cannot get past this step, post in the forums for some specific help.

After you’ve restarted your system with your manually configured voltages and returned to the BIOS, I always recommend going to the temp/voltage monitoring section and checking the CPU temp. If the temperature seems too high for your cooling, then shut the system down and double check that your cooling system is properly mounted, and making good contact. Moving on, almost all systems should be able to achieve 150MHz bclock stability with stock voltages, so go to the bclock adjustment and change it from 133MHz to 150MHz. Then save and exit and allow the system to reboot. This time, allow the system to boot fully into the operating system.

Testing for highest stable bclock frequency

Once the operating system has fully loaded, start up uXray. uXray should always be running while checking for stability of an overclocked system to ensure you do not overheat your CPU. uXRay shows your CPU’s core temperatures real-time, as well as the distance to TJ Max, my advice is to never exceed TJ Max. Now start up uXray, this will allow you to ensure that your overclocked settings have been properly applied, and that you are running at your desired speed. Check both the CPU tab for the expected CPU frequency (should be 1800MHz at this point), and check the memory tab to ensure your memory is running at the proper speed (uXray will show the frequency of the memory, not the DDR3 speed, it should be 450MHz at this point). Now start up your selected test program, for example Mprime. Run the test for just a short amount of time, five minutes should be plenty. Then reboot the system and return to the BIOS.

If the test ran without error, raise the bclock by 10MHz, reboot into your OS and run the test again. If the test failed, raise the CPU VTT voltage by a small increment, reboot into your OS and run the test again. You should be able to see where this is going, continue to raise bclock or CPU VTT voltage with a short test after each change, until you meet one of the following criteria:

  • You reach your desired bclock and successfully pass your stability test.

  • You reach your maximum safe CPU VTT voltage.

  • Raising the CPU VTT does not allow for additional stability.

Optimize Memory Frequency

DDR3 Basics

The next step is to find the limit of your memory. To do this, first you need to look at the memory’s ratings. DDR3 does not typically have a lot of overclocking headroom, so it’s important to start with stock settings. In this example I will use some basic Crucial Ballistix PC3-12800 for my explanations. This memory is rated for DDR3-1600 (800MHz) 8-8-8 24 1T with 1.65V. Enter the BIOS and adjust your memory timings according to the manufactures rating, in this case 8-8-8 24 1T. Now, consider your maximum/desired bclock frequency, 200MHz for example. This memory has a stock speed of 800MHz, so a 2:8 ratio with a bclock of 200MHz would put us right at that stock speed of 800MHz. You could set it and leave it there, but let’s say your maximum/desired bclock is not 200MHz. For example, if you are actually trying to reach 210MHz. If that were the case, the resulting memory frequency would be 840MHz (DDR3-1680). So, similar to finding bclock stability above, we need to work our way up to the desired speed testing along the way. There is an exception to this section, and that is with Clarkdale base Core i3 and Core i5 CPUs. They tend to have a very weak IMC, and are often times not capable of running memory even at their stock speed. If you have a Clarkdale based CPU, you may have to sacrifice memory speed to attain a good CPU overclock.

Testing for highest stable memory frequency

Theoretically we should be able to run for at least an hour with the bclock at 200MHz and the memory multi at 2:8– why? Because we already found out that this bclock speed is 1 hour stable, and we are not overclocking the memory yet.

However, the integrated memory controller (IMC) is powered by the CPU VTT voltage. So under some circumstances, especially with the newer 32nm CPUs, you may not be stable with your memory even at stock speeds due to the overclock imposed on the IMC. This is particularly true if you are running 4 DIMMS (P55/H55/H57), 6 DIMMS (X58), or 4GB DIMMS (P55/H55/H57/X58). If this is the case keep the memory at stock speed, or even try dropping the memory clock multiplier to run at less than stock speed, and increase the CPU VTT voltage until you gain stability. The newer 32nm CPUs seem to have particularly weak IMCs, and often will not run at the higher multipliers even if your memory is perfectly capable.

For testing memory, it is important that you take a break from whatever stability test you’ve been running, and use memtest86+ instead. The easiest way is to download the .iso and burn it to disc. Then configure your BIOS to load from your optical drive before the hard disk drive. When you boot the system with the disc inserted, memtest86+ should start automatically, and immediately begin testing your memory.

But, our goal is to reach 210MHz bclock, which will result in 840MHz memory frequency. In the BIOS, set your bclock to 202MHz, and your memory multi to 2:8, save settings and exit. Allow memtest86+ to load and complete one entire loop. A single loop can vary in length, and can take quite a while if you have a large amount of memory installed. If the test ran without error, press Ctrl-Alt-Delete and enter your BIOS. Raise the bclock by 2MHz and then save and exit. If the test failed, raise the memory voltage by a smallest increment possible, and run the test again. You should be able to see where this is going. Continue to raise bclock or memory voltage until you meet one of the following criteria:

  • You reach your desired bclock and successfully pass a single loop of memtest86+

  • You reach your maximum safe memory voltage.

  • Raising the memory voltage does not allow for additional stability.

  • Maximum safe memory voltage

What is the maximum safe memory voltage??? This is determined by two things:


  2. how much do you enjoy killing your memory? Throughout recent history, memory is probably the easiest component to damage with extra voltage. While there are exceptions, most newer DDR3 memory modules do not need very much voltage to reach their practical limits.

Once you have satisfied one of the three criteria above, drop the bclock down 2MHz from your last stable setting, and see if memtest86+ will run through 2 or 3 loops without error. If you wish to try to push your memory even further at this point, there is one more thing to try, and that is another bump in CPU VTT voltage. This will possibly boost the capabilities of the IMC and give you a little more room to overclock the memory. Otherwise - Congratulations! - you now have a relatively stable bclock frequency and memory frequency.

Stabilize CPU Frequency

The last step in this guide is often the first step for users who run into problems and then troubleshoot for days afterward. Leaving it to the last step makes the task much simpler. You now have the following settings locked in; CPU VTT, IOH voltage, memory voltage, memory multiplier, and memory timings. That means when we are looking for our highest CPU frequency, there are only two variables we need to play with: bclock and CPU voltage.

Right now your CPU multiplier should be very low, and your bclock should be quite high. If we move the CPU multiplier up right now, we would undoubtedly become very unstable, and unlikely to post. The idea here is that if your bclock and memory are stable with the current settings, shifting the bclock down should not cause any instability. So, change you bclock to 140MHz, and switch your CPU multi up to its maximum. In our example i5 750, the normal maximum would be x20. Intel’s Turbo feature allows for extra multipliers, and some BIOS will even allow for the higher multipliers to be forced. It will not hurt to use this feature if you desire. So with my example of the i5 750, with some BIOS, I would be able to lock in a multi of x21.

“Load-line calibration”

This actually goes by a few different names, but they are all meant as a means to reduce or prevent v-droop. Most overclockers would advise you to enable this feature; I would only recommend it if you understand what it does. It does typically allow for measurably higher overclocking, but at the cost of violating Intel’s design specs, and putting more stress on the CPU. However, overclocking in its essence violates Intel’s design specs, so you’re not breaking any new ground with this feature. I do not enable load-line calibration on my daily/gaming system. But I always use it when I am trying to fine the absolute limit. For more insight on the matter, refer to this excellent explanation at

CPU Voltage

That brings us to the first thing that most users want to play with after powering up their new system for the first time: CPU voltage, aka “vcore”. As you can see, this is actually one of the last things you should be changing. I would recommend starting at a nice and easy 1.3V. Surprisingly enough, many users are able to achieve very good overclocks with this modest amount of CPU voltage.

Testing for your highest stable CPU frequency

Once the operating system has fully loaded, start up uXray. Now start up uXRay and verify that your overclocked settings have been properly applied, and that you are running at your desired CPU, bclock, and memory frequencies. Now start up you selected test program, for example Mprime. Run the test for five minutes. Then reboot and go back into the BIOS.

If the test ran without error, the raise the bclock by 10MHz, reboot into your OS and run the test again. If the test failed, raise the CPU voltage by 0.025V, reboot into your OS and run the test again. Continue to raise bclock or CPU voltage until you meet one of the following criteria:

  • You reach your desired bclock and successfully pass your test.

  • You reach your maximum safe CPU voltage.

  • Raising the CPU voltage does not allow for additional stability.

  • Maximum safe CPU voltage

For there is no maximum “safe” CPU voltage in my book. My recommendation is to determine your maximum safe voltage based on your temperatures while running your stability test. With stock air cooling this could be as low as 1.3V on some i7 CPUs while running MPrime. Or it could be as high as 2.2V when attempting Super PI 1M with an i5 670 on liquid nitrogen. Personally, I don’t like to see my load temperatures exceed 90C on air or water cooling, but it’s really up to you.

Is it stable?

So, once you find your highest CPU frequency by meeting one of the criteria above, lower the bclock by 5MHz, and run your selected stability test until you are satisfied. If you are looking for a stable system as a power user or gamer, Mprime for six hours is more than sufficient in my testing, but you may run longer if you desire. But for a true test of stability, I always like to play Crysis while encoding a Blu-Ray movie into an mpeg4 format.

First Generation Intel Core CPUs (LGA 1156)

With the release of the Nehalem architecture in November 2008, Intel introduced a new naming scheme for its Core processors. There are three variants, Core i3, Core i5, and Core i7, meaning that Core i3 is low-budget, Core i5 is best value for money and i7 is top performer. Common features of all Nehalem based processors include an integrated DDR3 memory controller as well as QPI - Quick Pack Interconnect, using base clock instead of FSB (Front Side Bus) previous interface. Also, all these processors have 256 KB L2 cache per core, plus up to 12 MB shared level 3 cache. Because of the new I/O interconnect, chipsets and mainboards from previous generations can no longer be used with Nehalem based processors.First generation processors are have the following codenames:

  • Clarkdale

  • Arrendale

  • Lynnfield

  • Bloomfield

  • Gulftown

and are supported by LGA 1156 sockets. If you own a 1st gen Intel Core processor using Nehalem architecture, you're in the right page.

Let's start finding at first your base clock frequency. As far as you may be concerned BLCK (Base Clock) affects 4 crucial parameters:

  1. Memory

  2. Uncore

  3. CPU

  4. QPI

Let's have a little talk about them and try to isolate the bclock. We try to isolate this, cause we need to know our maximum bclk without any other concerns.

1] Memory isolation

Memory defines your RAM's frequency
Math Formula: bclock * memory_multiplier = RAM DDR speed

for example, having 1333 MHz DDR RAM frequency means that you have  bclk= 133 and memory multiplyer=10.  Doing the math, you have 10x133=1333 MHz. This is the value you don't want to overpass while testing blck. If your RAM runs at 1600 MHz, then 1600 is the value you don't want to overpass, and so on...

To isolate memory factor, please drop your memory multiplier down to the lowest value. This means that you can overclock base clock without being concerned of overclocking RAM simultaneously. Please DO NOT overclock pass your RAM's stock speed.

To delve into details and crystal clear your thoughts, let's analyse a real case scenario; so let's say you want to push your CPU at 4GHz. In overclocking language, this means you want to run the formula: 200 x 20 = 4 GHz (notice: bclk=200 & cpu multiplier=20). So, if you drop your memory multiplier down to 8x, your memory would be running at 1600MHz ( 200 * 8x ). So, you need to be aware of your RAM stock speed, in order to NOT overpass it !!!

2] Uncore isolation

Uncore,  means everything else but core. Such as L3 cache and IMC (Integrated Memory Controller) of the CPU.
Your Uncore freq should be >= of your 2*memory clock

Which means you must have at least the double multiplier of your memory. This is not trouble, because most motherboard force this formula automatically (even in overclocking) to protect your CPU from failure.

eg. Memory: 8x133

Uncore = 16 (or more) x 133

3] CPU isolation

Following our previous 4GHz scenario, you want 200x20, but let's we don't already know if our CPU is capable of operating that frequency. So, if you overclock your bclk up to 200 and PC fails to boot, you don't really know if this happened due to CPU inability to operate at 4GHz or motherboard's inability to stabilise blck at 200 MHz. Simply put, we do not want to overclock the processor -- not yet. The i5 750 stock speed is 133x20=2.67GHz, so please DO NOT go beyond this frequency. We want you to overclock the bclk, not the CPU. So, drop down the CPU multiplier to 12x .

Do you wonder why ?

Well, is obvious: 200*12x = 2.4Ghz which is < 2.6GHz stock freq .

4] QPI isolation

I do not know if there is a BIOS option for this to be refined. All I know is that QPI freq should not to change. So, if you are able to underclock its multiplier, you better do.


Last thing: set your Southbridge voltage to 1.3 Mhz.

Ok, Save and Exit. Go and test your new underclocked system. Stable enough ?

Baby steps

Start itching up your bclk with step of 15 MHz. Every time you overclock it you need to stress it, in order to test if the new bclock setting is stable. So use MPrime small FFTs instead of blend test.

As a rule of thumb you will hopefully catch up to bclock=150MHz without increasing any voltages.

If your system become unstable try to raise VTT. Nothing else.

Just VTT. Got it ? Intel claims that the max safe VTT is 1.35, but a lot of people use 1.4 as their safe-wall.

As long as you find the maximum VTT, then you are able to start overclocking your CPU. Once you know that your motherboard is capable of operating at 200 MHz base clock, you should start itching the CPU multiplier and test system's stability with small FFTs. Like that:

  • 200x12 = 2.4 GHz

  • 200x13= 2.6 GHz

  • 200x14 = 2.8 GHz

  • .....

  • 200x20 = 4 GHz

In case of instability or unable to post the bios, you need to increase the VCore. Please do not exceed 1.45 VCore. The more voltage you apply, the hotter your CPU goes. That's why overclockers need exotic cooling solutions like Liquid Nitrogen or Helium.

Maximum safe CPU VTT

What is the maximum safe CPU VTT voltage? Depends on a lot of things, but I feel like these are some basic conservative guidelines. If you’re running the stock Intel heatsink and fan, I would not advise more than +0.2V, if you are running a high end air cooler I would not advise more than +0.3V on LGA1156 platforms, and no more than +0.4V on LGA1366 systems. If you are running a high end custom water loop add another 0.05V to those values, and if you are using extreme forms of cooling then use whatever works best. I’ve used up to 1.70V on an i7 920, and up to 1.55V with my i5 750 with extreme cooling.

Fine tuning

After you have met one of the criteria above, you should have a rough idea of your bclock limit, now it’s time to get a little more fine tuned. Next, instead of 10MHz bclock changes, shift to 2MHz changes. Then repeat the steps above and search for one of the three criteria again. Also, ensure you check my note about “bclock holes” above, the same concept can be applied to this fine tuning step as well.

Second Generation Intel Core CPUs

Three CPU models here, Intel Core 2500K, 2600K and 2700K while the difference between them is the HyperThreading factor, meaning that 2500K has 4 cores /4 threads and 2600K has 4 cores/ 8 threads. Notice that the "K" skew means "overclockable", thus you need a "K" version of these processors. Speaking of "stepping" codes the existing Intel Sandybridge CPU has been classified into three categories:

  1. Full unlocked (i.e. the K series)

  2. Partial unlocked (the non-K 4 core)

  3. Locked (dual core) processors (like Core i3)

Intel simplified things so there is not really too much work involved to maximize the overclock capability of these three unloacked processors. Let’s start with the key power options:

[tabs tab1="VCore" tab2="VCCIO" tab3="VCCSA" tab4="VDRAM" tab5="PLL" tab6="PCH"]


Obviously, this is the main power source of the CPU, where 99% of CPU overclocking is dependent on. This is also the most vital voltage option for all overclockers on this platform. Sweet sport of voltage range for air /watercooling rig: 1.45 – 1.55 V


[tab]The power supplied to the CPU integrated memory controller and the PCI Express controller. This option has the default voltage of 1.05V, act very similar to what ex-VTT does, but much less important. The raise of this voltage can help to improve the stability when pushing the full 4 DIMM configuration to its max, such as 4x4GB@DDRIII-2300+ configuration. Sweet sport of voltage range for air /watercooling rig: 1.1V-1.2V[/tab]


This is the power to the system agent inside the CPU, which act as the supplement power for the memory controller and PCI Express controller. This option has the default voltage of 0.95V, however with no importance with respect to the overclock capability of the system regardless if it has been raised or lowered. You may as well drop this voltage to save some power for your system. After all, every little bit of power has their own share on your power bill. Sweet sport of voltage range for air /watercooling rig: <0.95V to as low as you can get without effecting system stability



This is the main power source for your DRAM, with the same characteristics as what it used to be on P55/X58 platform. Sweet sport of voltage range for air /watercooling rig: 1.65 V



This is the power of the internal PLL on the CPU. This option has the default voltage of 1.8V however, with no importance with respect to the overclock capability of the system regardless if it has been raised or lowered. You may as well drop this voltage to save some power for your system. Sweet sport of voltage range for air /watercooling rig: < 1.8V to as low as you can get without effecting system’s stability.



This is the power of the PCH controller. This option has default voltage of 1.05V, with no importance with respect to the overclock capability of the system regardless if it has been raised or lowered. You may as well drop this voltage to save some power for your system. Sweet sport of voltage range for air /watercooling rig: < 1.05V to as low as you can get without effecting system’s stability.[/tab]


Now, get into BIOS and setup your system ready for overclocking.

[toggle title="BIOS Enable/Disable"]


  •  Limit CPUID Maximum

  • Power Technology

  • C1E Support

  • OverSpeed Protection

  • Spread Spectrum



  • Internal PLL Overvoltage

  • Execute Disable Bit

  • Intel Virtualization Tech



Third Generation Intel Core CPUs

Ivy Bridge Overclocking is almost identical to Sandy Bridge overclocking. Simply put you only need to overclock the multiplier and not the base clock (BCLK). With these new Ivy Bridge chips, overclocking is a child's play into experienced hands, thus the whole procedure is a lot easier. For example  there is almost no need to increase the secondary CPU voltages, such as VTT. Even more, Ivy Bridge is more unlocked than Sandy Bridge, because it offers many more memory multipliers and even adds in a second divider so that you can run memory at different speeds in more friendly increments (like 2000 MHz and 2133 MHz). However under air cooling Ivy Bridge exhibits much higher temperatures during full load due to its 22nm process, which will probably only get better though cooling optimizations and better contact between the IHS and the CPU Die.

On Air/Water: When overclocking on air the only two voltages you should need to touch on an Ivy Bridge setup are the Vcore (which you increase) and the CPU PLL( which can be decreased to help temperatures).

TJ Max for Ivy Bridge is 105C, however you shouldn’t go above 85-90C load when overclocking.

What is increasing to increase the power is the current, you cannot control the current (Ampere), but you can control the frequency and voltage.

[toggle title="Under the hood of 22nm 3D Transistors!"]

Decreasing the size of the transistor can produce some undesirable results. When we reach the 22nm size, we are dealing with some quantum mechanics theories and when we do this we can talk about the Heisenberg uncertainty principle, which basically states we cannot simultaneously know the location and momentum(momentum=mass x velocity) of a sub atomic particle at a given point in time. That means that there is a certain level of uncertainty which must be applied, and we might not be able to know where the electron is at any given moment. If the electron is outside of where it should be, then we have higher leakage. There is an equation where temperature and leakage are related, and while it is pretty complex, it does allow us to analyze certain points easily.

Sub threshold Leakage= A (W/L) (k^2/q^2) T^2 e^((-qV_t)/nkT) In more simplified terms this shows us that leakage increase exponentially with temperature, and that voltage also has a significant impact on increasing leakage. This has been true for almost all microprocessors, however on Ivy Bridge it is easy to see.

We can see that not only is the temperature decrease having a great effect on the power consumption (representative of leakage), but also an exponential one, as at around -60C on both runs we see a leveling off of the power consumption. However as the temperature rises the increase in power is much more than it is when the temperature is lower. This confirms that the leakage on this CPU is very heavy, we can also see that the leakage is being decreased exponentially as we decrease the temperature.


Overclocking the IvyBridge Frequency:

On Ivy Bridge overclocking is done through the CPU Multiplier on a “K” series SKU like the 3770K and 3570K and the multiplier is multiplied by the base clock. When you overclock the base clock(BCLK) you are overclocking the DMI and PCI-E busses as well, so you might damage or corrupt the devices hooked up to these busses such as your HDDs/SSDs and GPUs on the PCI-E bus. That been told, please don't overclock the Base Clock, but CPU Multiplier instead.

CPU Frequency=CPU Multiplier X Base Clock

Memory Frequency= Memory Multiplier x Base Clock.

With Ivy Bridge, you want to slowly increase the VCore as temperatures will hurt your max OC much more than voltage can stabilize it. Thus, please increase one the multiplier at a time. If you end up with too much heat then the logical thing would be to decrease the voltage, however at this point you can try to decrease the CPU PLL, and if that doesn’t help much you can always decrease the VTT and System Agent (IMC) to levels where they are lower but still remain stable.

With just increasing the multiplier you can increase the clock speeds of the CPU up to about 4.2 GHz with 42x100.00. If you want a set 100 MHz even base clock it is best to set the base clock to 100.00. SVID will stabilize the CPU to about 4.2 GHz but not beyond that, so you will need voltage increase above 4.2 GHz. Pay attention though, that any overclocks above 42x will probably require VCore increase.

As we told you at BIOS Setup page, if you want the best results you should disable power saving options like I have below, however if you want the CPU frequency to drop under idle conditions, you should leave them enabled, but use fixed voltages instead of auto or offset values.

You will also want to set LLC (LoadLine Calibration) for a slight droop, or Extreme for no droop at all. The LLC on these boards is rock solid, and we recommend you to use it.

Final words

So when you get a board and want to overclock typically you need to verify and stabilize your tested settings. First off let us remind you that we always recommend increments of baby steps in CPU and memory (from the default base clock frequency upwards). In the first stage you overclock the CPU, in the second the memory. Once you get instant restart or a lockup, back down to the previous setting and typically that is your stable result in it's highest threshold.

Alternative (if you can allow for more noise), increase the fan RPM on the CPU towards a higher setting that you find comfortable. Cooling helps with overclocking, it's a s simple as that. That baclside of your graphics card howevere gets hot as well, so make sure your PC casing is well ventilated with decent airflow.

Overclocking tools - now you can't use any 3rd party tool like Windows, however without voltage tweaking and on-the-fly changes, we recommend you to stick to the BIOS settings.


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