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[Sticky] P55 Overclocking Guide

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Warning: Overclocking is something you do at your own risk. Intel does not officially support overclocking. Overclocking will void the warranty of your CPU. Then again, so does adding new CPU coolers and thermal paste.

Overclocking is becoming more common since it's a good way to alleviate CPU bottlenecks. Thankfully, overclocking on P55 based motherboards is not an extremely difficult task as you are about to see. For this guide, I am using the EVGA P55 FTW motherboard, Intel Core i5 760 and G.SKILL ECO 2 x 2 GB DDR3 1600 CL7 memory. Many of these terms and strategies apply to X58 overclockers as well.

Here is a good diagram of the architecture of Lynnfield (LGA 1156 quad core) processors. Unlike previous architectures, Lynnfield has both the memory controller and PCI-E controller.


Here is the architecture for Clarkdale, the LGA 1156 dual core processors. These have an onboard graphics solution.

Key Terms

Before overclocking, you should familiarize yourself with key terms. These are the things you may end up adjusting in the BIOS for your overclock.

  • CPU Frequency Setting: Speed of the base clock (BCLK) or quick path interconnect (QPI).
  • CPU Multiplier Setting: Multiplier used to determine CPU speed. Multiply the base clock by this value to get your CPU speed.
  • QPI Frequency Selection (aka CPU Uncore Frequency): Frequency of the L3 cache and integrated memory controller. Should be set to 2x the memory divider, making it 2x the memory speed. This can be rather confusing, read below for clarification.
  • PCI-E Frequency Setting: Speed of the PCI-E slots. Increasing this value might help maximize BCLK, but don't do any large increases.
  • Clockgen Switch Mode: This feature is not on many motherboards. Some motherboards have dual clock generators to allow you achieve higher BCLK speeds. Enabling this will allow you to pass 200 MHz BCLK.
  • C1E Support, SpeedStep and C-STATE Tech: Power saving features. Reduces CPU multiplier when idle. Overclockers prefer to disable this.
  • Turbo Mode: Adds 2x to the multiplier of the first core and 1x to the rest
  • VDroop: When enabled, this causes a drop in VCore in Windows. Again, overclockers tend to disable this.
  • Bootup CPU VCore: VCore during booting sequence. VCore is the voltage of the CPU core. This is one of the most vital voltages when overclocking.
  • Eventual CPU VCore: VCore after the system has booted into Windows. I always keep eventual and bootup VCore at the same settings.
  • DIMM Voltage: Voltage for memory. Your memory should not be rated for more than 1.65v.
  • Bootup CPU VTT: VTT during booting sequence. VTT is the termination voltage. It should always be set within 0.5v of the DIMM voltage. So if your VTT is set to 1.1v for example, the DIMM voltage can be no higher than 1.6v. Increasing the VTT is necessary for moderate to heavy overclocking. When using air cooling or something similar (no maintenance water cooler), most people don't like to go past 1.4v VTT.
  • Eventual CPU VTT: VTT after the system has booted into Windows. I always keep bootup and eventual VTT at the same setting. When using air cooling or something similar (no maintenance water cooler), most people don't like to go past 1.4v VTT.
  • PCH: Voltage of the P55 chipset or southbridge. Usually left at auto.
  • CPU PLL: Voltage of the clock generator. Usually left at auto.
  • CPU PWM Frequency: Frequency for the MOSFET for the CPU. Higher is cleaner power, but results in much higher MOSFET temperatures. Usually left at default setting when air cooling.
  • VTT PWM Frequency: Frequency for the MOSFET for the VTT. Higher is cleaner power, but results in much higher MOSFET temperatures. Usually left at default setting when air cooling.
  • DDR PWM Frequency: Frequency for the MOSFET for the memory. Higher is cleaner power. Usually left at default setting.
  • DRAM SPD: Profile for memory/RAM. Some RAM kits have XMP Profiles which have specific speed, timings and voltage.
  • DRAM Frequency: Setting of RAM divider. This gives you your RAM speed. To calculate RAM speed, see below.

CPU Speed Calculation

You should know how to calculate CPU speed before overclocking. It's a very easy task. In the BIOS, multiply the base clock by the multiplier setting and that gives you your CPU speed. Here is an example of my i5 760.

133 MHz BCLK x 21 = 2800 MHz or 2.8 GHz

Now factor in turbo mode. Just increase the multiplier by one.

133 MHz BCLK x 22 = 2933 MHz or 2.93 GHz.

QPI Frequency Calculation

Determining the QPI Frequency may be unclear at first. So let me clear that up. It is referred to as QPI Frequency in many motherboards, but some may call it Uncore Frequency. It is the speed of the L3 cache and integrated memory controller. So in the BIOS You have three options here - auto, 4.270 GT/s and 4.800 GT/s. 4.270 GT/s is a 16x multiplier while 4.800 GT/s is an 18x multiplier. So to determine QPI frequency, use this equation.

BCLK x QPI multiplier = QPI frequency

QPI speed should be double the effective speed of your RAM. To get this, it should be twice the speed of your RAM divider. Now let me plug in some numbers for an example.

200 MHz x 16 = 3200 MHz QPI speed

Perfect for me, since I have 1600 MHz RAM.

Memory Speed Calculation

The memory speed is determined by a divider. You can choose between 2:6, 2:8 and 2:10. Take the last number and multiply it by the BCLK speed. So lets use 2:10 as an example, which was the default setting for me (well auto used 2:10).

  • CPU Frequency Setting: 133 MHz
  • CPU Multiplier Setting: 21
  • DRAM Frequency: 1333 MHz (2:10)

So those are my default settings. So as stated above, I have to take the last number of the RAM divider (in this instance, 10) and multiply it by the BCLK which is 133 MHz. 133 MHz x 10 = 1330 MHz.

Relationship of Watts and CPU Degrees

If you look up the specifications of processors, you will see a TDP (Thermal Design Power) rating. This is the maximum power usage and heat the CPU can give off. If your CPU has a 95W TDP for example, that doesn't necessarily mean it will give off that much heat or use that much power. It just won't use more than that or give off more than 95W of heat. It's a category. All Lynnfield quad core processors fall within a 95W TDP.

Now for this section, you can find out how to calculate the maximum heat load for your CPU which is close to the amount of power your CPU will use. I must thank EVGA forum member lehpron for teaching me and many others these equations. Here is the equation.

TDP x (overclocked BCLK/stock BCLK) x (overclocked VCore/stock VCore) ^ 2

So lets say your CPU has a TDP of 95W, the stock BCLK is 133 MHz and the stock VCore is 1.1375v. Lets say you get it up to 4 GHz (200 MHz BCLK) and you need 1.3 VCore.

95W x (200 MHz/133 MHz) x (1.3v/1.1375v) ^ 2 = 186.588921W or about 187W

So as you can see, that's a large increase in heat and power consumption. Anything to worry about? Depends on your cooler and fans. But most enthusiast air coolers (and water cooling systems with 120mm radiators) are rated for an effective heat dissipation of > 200W with the right fans.


Finally, time to overclock. Well... not yet. First make sure that Windows doesn't automatically restart upon crashing. It is important to see BSOD codes since they can help you determine your error. To turn off the automatic restart, go to System Properties -> Advanced -> Startup and Recovery (Settings).

It is also important to know the revision of your processor, since newer revisions might overclock better and use less voltage. Take a look at the LGA 1366 platform for example (X58). The first processors, revision C0, were the i7 920, i7 940 and i7 965. They usually required around 1.4 VCore or even higher to achieve a 200 MHz BCLK. Revision D0 on the other hand, which includes newer i7 920 chips, i7 930, i7 950, i7 960 and the i7 975, only require around 1.3 VCore to achieve 200 MHz BCLK. And as the equations above depict, this reduction of voltage really translates into much less heat and power consumption. Thankfully, all Lynnfield processors have around the same voltage requirements (it always varies, but they're all in the same ballpark) and all Clarkdales also are within the same ballpark as of right now.

Sorry, we're not overclocking yet. Before overclocking, you should download some useful tools. You should have CPU-Z since it displays lots of vital information. A temperature monitoring program is highly recommended. RealTemp and CoreTemp are the best. Finally, get some stability testers. These apply a very heavy load on your CPU. So here are the programs I use.

  • CPU-Z - Displays information about your CPU, motherboard, memory and graphics card(s).
  • RealTemp - Displays CPU temperatures, CPU core temperatures, GPU temperatures, has adjustable sensors for CPU speed, CPU temperatures, adjustable TJMax and more.
  • Prime95 - Stability tester. Several different tests including small FFT CPU test, large FFT CPU test and blended CPU/RAM test. I recommend running this for a good 12 hours on all modes to ensure a stable overclock.
  • IntelBurnTest - Modern and relatively easy to find Linpack. Along with LinX, this is the most stressful CPU test out there. I recommend running this for at least 20 passes.

Always make sure your CPU cores stay below 85 degrees Celsius when stress testing. Before overclocking, go to your BIOS (press Del during boot sequence), load default settings and reboot. Then go back into the BIOS and set your memory to the official timings and voltage going by the specifications provided. Then go to the CPU configuration tab and disable C1E support, SpeedStep and C-STATE tech. You should also disable turbo mode if you are going for moderate to heavy overclocks. Also check your fan speeds and make sure they're where you want them. Now lets begin.

Finding maximum BCLK/QPI speed

  • Lower CPU multiplier to lowest setting.
  • Use one of the stability testers to make sure it's stable.
  • Increase BCLK by 10 MHz.
  • Use one of the stability testers to make sure it's stable. If unstable, raise VCore to the next increment.
  • Repeat the last two steps until you can't go any higher. At this point, go back to the last stable settings and raise VTT voltage to the next increment. If stable, increase BCLK by 10 MHz again. If unstable, raise VTT to the next increment.
  • Use one of the stability tester's to make sure it's stable. If unstable, raise VCore to the next increment.
  • If you still can't go any higher, go back to the last stable settings and increase VTT again.
  • Repeat the last three steps.

If you did the above strategy, you will then come to your max BCLK speeds. Once this is done, you can then start to increase the multiplier. Increase it to the next increment, and use the stability testers to ensure stability. Once unstable, raise VCore to the next increment. Repeat this until you come to a point where VCore increases are useless, then raise the VTT to the next increment.

If you're an impatient person with a high end P55 motherboard, you won't want to take these baby steps when overclocking. For Lynnfield processors, you can try to jump straight to 200 MHz QPI. If you do this, I recommend making the following changes.

  • CPU Frequency Setting: 200
  • CPU Multiplier Setting: Whatever the maximum is, it's usually default unless you have an unlocked chip (i5 655k or i7 875k).
  • VDroop Control: Without VDroop
  • Bootup CPU VCore: 1.30000v
  • Eventual CPU VCore: 1.30000v
  • DIMM Voltage: Use rated specification, but must be higher than VTT
  • Bootup CPU VTT: 1.30000v
  • Eventual CPU VTT: 1.30000v

That probably won't be stable, but it's a good starting point. Then run a stability tester. If unstable, raise VCore to the next increment. Keep raising the VCore until raising it shows no more progress. Then raise the VTT. You should come across a stable overclock this way in a matter of time, as long as temperatures are in check. If not, increase PCI-E frequency to 104 MHz and try again.


BSOD = Blue Screen of Death

This occurs when your system is unstable. They provide some useful information such as the error encountered and a code which can help you identify the cause. The following codes have been identified by TechPowerUp using the X58 platform. The code may or may not be the same for the P55 platform, but the error encountered is what we're looking at.

Increase VCore if you see this BSOD.

Increase VCore or VTT if you see this BSOD. Start with VCore increases first. If there is no progress, then try increasing VTT.

So that's not too bad is it? P55 overclocking isn't too difficult with the right equipment. Be sure to choose a high end motherboard, good CPU cooler and good fans. If you want some CPU cooler recommendations, see this guide. Look here for fan recommendations. Best of luck to you...

Topic starter Posted : 26/09/2010 1:55 pm