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

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 10×133=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: 8×133

Uncore = 16 (or more) x 133

3] CPU isolation

Following our previous 4GHz scenario, you want 200×20, 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 133×20=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:

  • 200×12 = 2.4 GHz
  • 200×13= 2.6 GHz
  • 200×14 = 2.8 GHz
  • …..
  • 200×20 = 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.


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