How to Overclock - Intel Core i7, i5, i3 CPU Overclocking Guide


If you're like most people, you've probably spent hours scrolling through the endless search results trying to find an overclocking guide or tutorial that covers everything you'll need to know about how to overclock your new Intel Core i7, i5, or i3 processor (CPU). However, most of them only scratch the surface or expect that you already know a lot about the subject, so you're left to search for another guide that covers the missing pieces.

Intel Core i7, i5, i3 CPU

Well, if you're trying to overclock any of the following CPUs, we've got you covered, and along the way, we'll explain everything you'll need to know about overclocking your specific LGA 1156 based CPU:

  • Lynnfield's 45nm Quad Core i7 CPUs: i7-875K, i7-870, i7-860
  • Lynnfield's 45nm Quad Core i5 CPUs: i5-760, i5-750
  • Clarkdale's 32nm Dual Core i5 CPUs: i5-680, i5-670, i5-660, i5-661, i5-650, i5-655K
  • Clarkdale's 32nm Dual Core i3 CPUs: i3-550, i3-540, i3-530

We're also going to ignore the status quo and question some of the key assumptions that most guides just assume to be valid, such as:

  1. Should you enable load line calibration to help reduce vdroop?
  2. Does disabling all of the power saving features, such as SpeedStep, C1E, and C-States, really give us a higher overclock?
  3. Is disabling Turbo Boost always the best route to take when you're trying to achieve your maximum overclock?

While some of these features may have been detrimental in the past, is this still the case? The technology has come a long way in the last couple of years, so the answers to these questions may have changed, and we may actually be able to use these features to our advantage.

Well, enough questions. Let's move on and see what we're able to find out.

Understanding the Basics

Before we get started, there are a few prerequisites that we need to get out of the way. The following guides are designed to get you up to speed fast on all of the basics you'll need to know before you start overclocking your system.

  1. Turbo Boost, BCLK, & QPI: Exploring Intel's Core i7, i5, & i3 CPUs - Covers all of the basics of Intel's Clarkdale and Lynnfield architectures that are important for overclocking, such as BCLK, QPI, multipliers, turbo boost, and how the CPU frequency is determined.
  2. Vcore, VTT, DRAM, PLL, PCH – Voltages Explained – Core i7, i5, i3 - Goes over all of the important voltages that you'll need to change as you're overclocking.
  3. RAM, CPU Stress Testing - Software, Tools: Prime95, Intel Burn Test - Explains about all of the common overclocking software and tools for system monitoring (CPU-Z), temperature monitoring (Core Temp), and stress testing (Intel Burn Test, Prime95, and Memtest86+).

If you're unfamiliar with any of these topics, then you should read the necessary guides before going any further.

Hardware We're Using for this Guide

If you're interested, here's the hardware we're using for this guide.

CPU Intel Core i5-760 2.8GHz LGA 1156 95W Quad-Core Processor
Cooler CORSAIR CWCH50-1 120mm High Performance CPU Cooler
Motherboard ASUS P7P55D-E Pro LGA 1156 Intel P55 SATA 6Gb/s USB 3.0
Memory G.SKILL ECO Series 4GB (2 x 2GB) DDR3-1600 7-8-7-24 1.35v
Video Card GIGABYTE GeForce GTX 460 (Fermi) 1GB GDDR5 GV-N460OC-1GI
Storage Crucial RealSSD C300 CTFDDAC128MAG-1G1 2.5" 128GB SATA III MLC SSD
Power Supply CORSAIR CMPSU-750TX 750W
Case Antec Nine Hundred Two
Monitor ASUS VH242H Black 23.6" 5ms HDMI Full 1080P Widescreen LCD w/Speakers
OS Microsoft Windows 7 Home Premium x64

Getting Ready for the Overclock

As mentioned before, in order to overclock the CPU, we're going to have to increase BCLK (since Intel usually locks the maximum multiplier that you can set), and BCLK and the multiplier are the only things that determine the processor speed.

So here's what we're going to do:

  1. First, we'll stress test our system to make sure we're starting from a fully stable system.
  2. Next, we'll figure out our system's maximum BCLK.
  3. Lastly, we'll find the maximum overclock for our CPU.

By doing each of these separately, we'll be able to only concentrate on a few variables at a time, which will reduce a lot of the complexity and random guess work. Make sure that you only change one thing at a time, so when something goes wrong, you'll know what caused it.

Disable CPU Spread Spectrum

Before we get started, it's good idea to disable one setting in the BIOS that can sometimes cause stability problems when overclocking: CPU Spread Spectrum. This feature is meant to reduce interference with other electrical equipment that's nearby, but it can reduce your maximum overclock, so it's usually best to turn this feature off, and it usually doesn't do any harm.

Make Sure Your System is Fully Stable

First, let's stress test the CPU to make sure it's in good shape. As mentioned in the stress testing guide, I'd recommend using Intel Burn Test for this. Make sure that you can pass the stress test on at least high.

To test the overall system stability, let's use the quick Prime95 system test. Run this test for at least 20 minutes. 20 minutes isn't enough to guarantee stability, so you can run it for longer if you want, but it should catch any obvious problems with your system before you start to overclock it.

Determining Your Maximum BCLK

We have another guide that goes over Determining Your Maximum BCLK, so go ahead and read that guide now. When you're done, we'll explain how to overclock the processor.

Overclocking the CPU

Now that we know our maximum BCLK, let's get on to the real reason you're here: overclocking the CPU.

As mentioned in the introduction to this guide, we have a number of options here, such as:

  1. Should we turn on load line calibration to help reduce vdroop?
  2. Is it worth it to overclock with the power saving features disabled (SpeedStep, C1E, and C-States).
  3. Will overclocking with turbo boost hold us back?

These are all important topics that most guides don't really consider, so if you're interested, we have two really good articles on the subject:

  1. Vdroop and Load Line Calibration: Is Vdroop Really Bad?
  2. Should you Overclock with SpeedStep, C1E, or Turbo Boost Enabled?

Overclocking with Turbo Boost Disabled

Overclocking without turbo boost is pretty easy because we only have to worry about one CPU multiplier. Go ahead and set your multiplier to the maximum you can. Some motherboards let you use the lowest turbo multiplier (even with turbo boost disabled), so if yours does, go ahead and use that; it may help you achieve a higher overclock if BCLK is limiting you.

Enabling the turbo multiplier on an ASUS P7P55D-E Pro

On an Asus motherboard, such as the P7P55D-E Pro we're using for this guide, you need to limit C-States to only the C1 state, in order to be able to lock in the turbo multiplier when turbo boost is disabled. This will reduce some of the power saving features because your CPU cores won't be able to go into as deep of a sleep as they could before, so I don't recommend doing this if you don't need to.

Limiting C-States to only the C1 state will also disable turbo boost, so make sure you set this back to auto if you ever want to try and overclock with turbo boost enabled.

Set your vcore manually

Now is also a good time to set your vcore manually (instead of leaving it on auto). Motherboards usually increase vcore too much on their own, so we want to take control of this for a serious overclock. If your motherboard uses a dynamic vcore, set it to the smallest increment above 0, so that we're basically at the stock voltage. If it doesn't, set your vcore to whatever voltage it would use by default (usually called the CPU's VID).

Start overclocking by adjusting BCLK

Since our multiplier is now set, we'll be manipulating the CPU speed with BCLK. Let's lower BCLK to 150 for our first stability test. Most processors should be able to do this without any additional voltage. Make sure you keep the VTT (aka IMC) voltage at the voltage you determined for your maximum BCLK.

Stress the CPU with Intel Burn Test

Now, run through a standard Intel Burn Test stress test. If you pass without any errors, go back to the BIOS and increase BCLK by 10. If it fails, increase vcore by 0.025 V and run the stress test again.

Consider increasing PLL if you can't get the system stable

Once you get to the BCLK range of 180 to 200, you may also need to start increasing your PLL voltage (if you're having problems getting the CPU stable with added voltage). Increasing it can help to add stability. Its default value is 1.8 V, and if you do have to increase it, most people never have to increase it over 1.9 V, so just keep that in mind.

Keep doing the above procedure until you reach one of the follow limits:

  1. You hit your maximum safe voltage. Intel's absolute maximum for this is 1.4 V.
  2. You reach your maximum safe temperature. 75 - 80 C is probably good to use as a maximum if you're running IBT and this is for your everyday overclock. Your temperatures should never get this high with any other program, so you should be in good shape. If you're needing to go much higher than this to get the overclock that you want, I'd recommend investing in a better cooler.
  3. Increasing vcore doesn't help anymore.
  4. You reach your maximum BCLK.

Once you hit one of these limits, back off to your last stable BCLK, and go up by 5 instead of 10. If this is stable, start going up by 2. If it fails, start going down by 2 until you reach your new limit. This process will help you zero in on your maximum CPU speed.

Overclocking with Turbo Boost Enabled

Overclocking with turbo boost enabled is slightly more complicated because we now have to worry about multiple multipliers, instead of just one, so we'll need to make sure that the system is stable under all of them.

If you remember from the turbo boost introduction earlier in the guide, there's a maximum turbo multiplier depending on how many cores are busy.

Max CPU Multiplier (by active core count)

CPU Model Default 4 Cores Active 3 Cores Active 2 Cores Active 1 Core Active
i7-870/875K 22 24 24 26 27
i7-860 21 22 22 25 26
i5-760 21 22 22 25 25
i5-750 20 21 21 24 24
i5-680 27 NA NA 28 29
i5-670 26 NA NA 27 28
i5-660/661 25 NA NA 26 27
i5-650/655K 24 NA NA 25 26

Luckily, all of the CPUs use the same multipliers when 3 or 4 cores are active, so that means we'll only need to test the 4 core case, which will save us some time.

So that leaves us with three cases to test:

  1. Only one core is busy.
  2. Two cores are busy.
  3. All four cores are busy.

To overclock with turbo boost, just follow the same instructions in the regular overclocking section. And to make things simpler, you can just stress test with one thread until you get near your upper limit. At that point, you'll probably have to start testing with the other scenarios we just mentioned.

Stress Testing

Now that we've found our maximum overclock, we need to thoroughly stress test the CPU and system to make sure they're fully stable. I'd recommend running the thorough Intel Burn Test and Prime95 stress tests for at least 20 minutes. 20 minutes isn't long enough to ensure stability, but we're not done stress testing yet, so it's enough for now.

If either of these fails, try to up vcore and try it again. I've seen systems pass Intel Burn Test all day, which is supposed to stress the CPU more than any other program, and still fail Prime95 in less than a few minutes, so don't be surprised if this happens.

Making Sure the Memory is Running at its Best

The memory multiplier should still be at its lowest setting at this point, since we never changed it from the BCLK maximization step. If it is, it may be lower than it needs to be, so now's a good time to set it to a more appropriate number.

If you're interested in overclocking your memory, now's a good time to do that, since the CPU and BCLK are basically stable. We have another guide on that subject: Memory (RAM) Overclocking Guide - DDR3, so check it out if you're interested.

If you're not interested in overclocking your memory, go ahead and set your memory speed as high as possible without overclocking it.

Stress Testing (continued)

Let's now finish the Prime95 system stress testing.

Lower your current BCLK by 2-5 (to give yourself some breathing room) and run one last thorough Prime95 stress test for at least 4 hours. Some people like to run theirs 8 - 24 hours, so run it as long as you need to feel stable.

If this test passes without a hitch, your CPU and system as a whole appear to be fully stable, so it would probably be a good idea to save a copy of these settings in your BIOS.

Final Thoughts

So there you have it. You just learned pretty much everything you need to know about overclocking your CPU and how to do it with or without turbo boost enabled. And if your motherboard supports dynamic vcore, you may have even been able to leave all of the power saving features turned on, so you're getting the best of both worlds.

If you didn't overclock your memory earlier in the guide and are interested in learning how to do that next, then make sure you check out our RAM Overclocking Guide.

This guide was designed to teach you everything you'd need to know to overclock an i7, i5, or i3 processor. If you have any questions, comments, or suggestions, feel free to let us know by leaving a comment.