Basic Overclocking Guide for Intel C2D Processors Page: 1

Today we will be showing you the basic steps of overclocking a Core 2 Duo processor on a motherboard using an Intel chipset (i975X). Overclocking should be done with extreme care and caution. An unstable overclock can create a lot of problems including corrupt hard disks, hardware failure, and other nasty things.


With that out of the way, let's get started!


The BIOS (Basic Input/Output System) is the area we will be focusing on for our overclocking in this guide. There are Windows software utilities that will allow you to overclock from within Windows but it is not advised. Changing the settings in the BIOS are permanent and give you a much wider control to help stabilize your overclock.

Most motherboard manufacturers use BIOS's that are very similarly layed out. In this guide the screenshots you will be seeing are from the BIOS of Abit's AW9D-MAX motherboard. You may need to locate the appropriate areas for some of the shots you will see as they may not be in the same place on your specific motherboard.

Below is what most BIOS's main screen looks like.

BIOS Main Screen

Let's move on and have a look at what some of these areas do and what needs to be changed.

Basic Overclocking Guide for Intel C2D Processors Page: 2
Basic BIOS Settings

There are a few areas that we need to change a few options in that will allow us a higher stable overclock. You can do these in any order that you please.

BIOS Advanced Features

The first thing we need to do is disable the Core 2 Duo's advanced CPU features. On my board this area is found under "Advanced BIOS Features > CPU Feature". Once in this menu you will find 3 key items that should be DISABLED: Limit CPUID MaxVal, C1E Function, and EIST Function. The other two options in between are undecided whether or not they make a difference to the overclocking abilities of this CPU. By default these settings are enabled, I have disabled both of mine. Disregard the Thermal Management setting.

BIOS CPU Features

That's it for the basic settings. Changing these few options will greatly increase your maximum overclock potential. Next we will look at some RAM timings and discuss what might work best for your setup.

Basic Overclocking Guide for Intel C2D Processors Page: 3
RAM Timings

Ram timings are key to a fast, stable overclock on any computer with any processor. What we need to make sure of before we start overclocking is that we loosen up the timings slightly to factor out the possibility of the RAM's timings being to tight to allow a higher overclock. This is going to be different with every single setup and each different kit of RAM. I have found that the best settings to start with are usually 5-5-5-15 as this is loose enough to allow a good bump in memory speed without hitting a wall.

On the AW9D-MAX the timings page can be found under "Advanced Chipset Features".

RAM Timings

Make sure that you select "Manual" so that you have control of the timings and not your motherboard. This specific board will try and automatically scale the RAM timings with the FSB/Memory speed which is bad when trying to overclock. As you can see from this screenshot I've decided to lower my timings to 4-4-4-10 which are my tightest stable timings at 445mhz FSB with 2.2vdimm. Again, I suggest timings of 5-5-5-15 to start off with and then gradually tighten them after you've achieved your maximum stable overclock.

Note for Asus P5W DH Owners: This motherboard has an FSB wall at 330mhz which can be overcome by enabling SPD in the advanced chipset features page.

Now, think you're ready to start clockin'? Let's get you familiarized with the settings first...

Basic Overclocking Guide for Intel C2D Processors Page: 4
Overclocking Overview

Let's get familiar with the settings listed in your overclocking panel before doing anything else. Head in to your BIOS's overclocking panel, on Abit motherboards it's the uGuru Utility. Your page should look somewhat similar to this option-wise:

BIOS Overclocking

Please do note that the speeds and settings shown in these pictures are not reminiscent of what you should expect or immediately try. These are my own personal settings and we will be covering each of the settings on this page one-by-one.

External Clock: This is what is known as the FSB (Front Side Bus) speed. This number is what controls your actual CPU clock speed.

Multiplier Factor: This is the CPU's multiplier. This number by default will be different depending on which CPU you have purchased (ie. E6300=7x, E6400=8x, E6600=9x, E6700=10x, X6800=11x, etc). Depending on your motherboard the multiplier can be lowered, but never raised unless you have an Extreme Edition CPU.

N/B Strap CPU As: This is what's referred to most commonly as the Northbridge's "boot strap". This is the clock speed of Northbridge itself. Setting this to your motherboards highest allowed option is always a good idea as it's going to reset the chipset to an already overclocked state rather than resetting to it's base clock frequency. To put this simply: The faster the Northbridge speed, the higher you should be able to raise your FSB speed.

DRAM Spec: This is where you can set your RAM divider. This indicates how fast the memory operates in contrast to how fast the CPU is operating. This option is going to vary by board manufacturer as to what works best. Some boards don't like 1:1, some don't like 2:3, and some don't like 4:5. Play around with this or do some research on your board to see which option people are getting the best results with. Just keep in mind that if you are going to use anything above 1:1 you need to have RAM capable of very high clock speeds.

CPU Core Voltage: This allows you to set the voltage in which your CPU receives. More voltage usually means the ability to clock further. However there may be other limiting factors and raising this option to high without the proper cooling can KILL your CPU. So please use caution when setting this value. This value is commonly referred to as "vcore".

DDR2 SDRAM Voltage: This allows you to set the voltage in which your RAM receives. The same goes for this value as with the CPU value, setting the voltage too high can cause your memory to overheat and prematurely die. Make sure you have adequate airflow around your memory when running anything above 2.2v This value is commonly referred to as "vdimm".

MCH & PCIe 1.5v Voltage: This allows you to set the voltage in which your chipset receives. Most Intel chipsets thrive on voltage and raising this value can almost exponentially give you greater overclockability. But again, same as with the CPU and RAM values, setting this to high without adequate cooling can result in a dead or crippled motherboard. This value is commonly referred to as "vmch".

Now let's look at the benefits and side effects of changing some of these values.

Basic Overclocking Guide for Intel C2D Processors Page: 5
Overclock It!

You should now have a basic understanding of what the values in your overclocking panel actually do. Let's look at the proper way to change these values safely.

BIOS External Clock

Increasing the external clock speed (FSB herein) will in turn also increase the speed of which your memory runs. To start off I suggest increasing this value in 25mhz increments until your computer is no longer stable or no longer boots. Once this happens back down the FSB 25mhz, adjust/tweak the options I am about to talk about, and then start raising the FSB in 5mhz increments until you loose stability or the computer no longer boots.

Changing (lowering) the CPU multiplier is not recommended on chips with multipliers of 9 or less unless you have a motherboard capable of running at very high FSB speeds. Lowering the multiplier does benefit you in the way of being able to run higher FSB and memory speeds for enhanced bandwidth and throughput but as of current most motherboards can't operate at FSB speeds high enough to take advantage of lowering the multiplier.


Setting your NB strap to your boards highest selectable value will greatly benefit you in running higher FSB/Memory speeds, so get this set pronto. Most Intel chipset based boards currently top out at 1066, and a few select boards have a maximum strap of 1333 which is even better.


Most motherboards by default will have the DRAM Spec set to DDR2 800 which is a divider of 2:3, making your RAM run as fast as it possibly can. This setting usually needs to be decreased in order for your RAM to stay within specification when higher FSB's are used.


I have found on my motherboard that I can achieve the highest stable overclock when my DRAM Spec is set to DDR 533 which is a 1:1 divider (the CPU and memory are running at the same speed). This allows me to increase the FSB without fear of topping out my RAM's max speed and also allowing me to tighten the RAM timings a bit because it's not running at it's maximum rated speed.

You will need to play with these options yourself as all motherboards perform differently with different dividers given what RAM is being used and how fast it is capable of operating. A quick google search should pull up enough information from other users who have tested all of the values to know which works best on your board.

BIOS Vcore

Setting a higher vcore value is another one of those almost sure-fire ways to help push the limits of your CPU's overclockability. Keep in mind that more voltage = more heat. You MUST have adequate CPU cooling in order to boost this value or else you risk damage to or complete failure of the CPU. All motherboards have a different range of selectable vcore values, and using more than 1.5v on good air cooling is not recommended (I personally ran 1.55vcore with a Scythe Infinity and never had a problem, evaluate your situation carefully and decided whether or not you can go above the 1.5v level). If you have a good watercooling setup the recommended maximum vcore is roughly 1.65v.

For TEC/Pelt users the maximum recommended vcore setting is around 1.7v and phase/cascade/dice/ln2 users should evaluate the cooling capacity of their units and adjust the maximum vcore accordingly.
BIOS Vdimm

Increasing the vdimm allows you to do a few things. The first thing being that your RAM can usually operate at a speed higher than what the manufacturer has rated. The second in some cases will also allow you to tighten your timings past what the manufacturer has specified. Most DDR2 modules will run at their peak performance level in the 2.2v area. Some IC's prefer more volts, and some less. I recommend testing what your RAM can do at 2.2v and going from their. If you plan on running your memory at a voltage higher than 2.2 make sure you have adequate cooling apparatus and good airflow as RAM is highly prone to problems when overheating.


Intel chipsets love extra voltage, it's what allows the chipset to run at extremely high FSB speeds. Upping this voltage is definitely recommended within reason. If you have a way to actively cool your chipset heatsink or have an aftermarket cooler you shouldn't have any problem maxing this voltage. If you are running the motherboards stock cooler a safe recommended value is 1.75v or less. I have rigged up a high speed 30mm fan over my chipset and feel that 2.0v is a safe value in my situation as the heatsink stays cool to the touch.

That's pretty much it! With the proper use of these settings you should be able to achieve a decent overclock depending on the quality of parts used in your system. Just try to remember to stay within reason when changing these settings. Also don't get frustrated easily if you can't instantly overclock to 4ghz especially if this is your first time overclocking. It takes time to figure out what settings works best for your setup, and everyones results will vary. Get used to what all of these settings control and the outcome of changing the given setting. Write down the outcomes if you have to so that you can remember what works and what doesn't work.

One last thing, don't forget to save your settings! ;)

BIOS Finished

If you have any questions, comments, or concerns please feel free to discuss them on our forum, thanks!