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Intel Core-i3/i5/i7 LGA1156 Overclocking Guide E-mail
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Written by Servando Silva   
Tuesday, 24 August 2010
Table of Contents: Page Index
Intel Core-i3/i5/i7 LGA1156 Overclocking Guide
Why Should I Overclock?
Overclocking Applications and Utilities
Processor Stability Testing
Understanding OC Variables
OC Testing Methodology
Overclocking Frequency vs. Voltage
Overclock vs Power Consumption
Overclock vs Temperatures
Final Thoughts

Understanding OC Variables

There are some basic variables you should really check while overclocking. Based on these variables, you'll be able to achieve 90% of your overclocking process and actually reach a stable and very decent frequency without messing a lot with weird numbers and values. Please refer to your motherboard's manufacturer to locate the BIOS reset switch/jumper before starting to overclock. This jumper will be very helpful if you reach a completely unstable state were the PC won't BOOT anymore. Don't panic, just turn off your computer and press/short the appropriate pins to reset your settings. Some other manufacturers implement an auto-recovery feature which (in case the PC doesn't BOOT) will recover your settings after trying to POST a pair of times without achieving it.

Now you should really have a look at your BIOS and identify the section where all the next parameters are found. If there's a possibility to save different profiles (many motherboards feature multiple OC profiles) save a copy of your default's profile.

CPU Frequency: This frequency is calculated by multiplying CPU multiplier x BCLK. Until Intel LGA775 sockets, this frequency was calculated by multiplying CPU multiplier x Front Side Bus. Intel Core i7 processors changed this FSB for a Base Clock (BCLK) which is the basis to all the parameters I'll explain below. CPU frequency is 100% related to overall speed, and thus, it's the most important factor when overclocking your setup.

BCLK: This value is the key to obtain all other values, since all of them are BCLK multiples. Low-end motherboards should reach around 170-180MHz BCLK, while high-end motherboards easily do 200+BCLK. Considering how high CPU multipliers are nowadays, a BCLK of 200MHz should be enough to reach decent speeds. Going above this might require increasing voltage on many motherboards.

QPI Frequency: QPI means Quick Path Interconnect. This is the newest Intel communication path which now communicates the CPU with the memory instead of passing through a North Bridge. QPI increases speed and bandwidth, so it is a very important value to be checked if you want the best clock's performance.

Uncore Frequency: CPU-Z reports Uncore Frequency as Northbridge frequency, which is false because there isn't a NB in P55/H55 motherboards. This value represents on-die memory controller's frequency and L3 cache's composing QPI frequency at the end. Similar to QPI and CPU frequencies, Uncore frequency is a Base Clock's multiple and it needs to be set at least twice the value of RAM frequency. Otherwise, your PC won't even BOOT. Increasing Uncore frequency gives a boost on overall performance similar to QPI frequency, but it can't be raised a lot. Example: If your memory runs at 1600MHz, your Uncore frequency should be equal to 3200MHz at least.

CPU Multiplier: As its name says, this multiplier gives you the final CPU frequency value. For Intel Core i7 processors, this multiplier is higher than LGA775 CPUs. This means BCLK doesn't need to be as high as FSB to reach outstanding frequencies. Normally, Intel determines a minimum of 20x for low-end CPUs while it can be set up to 25x-26x for high-end CPUs. Intel recently launched unlocked multiplier processors like the Core i5 655K used in this article. Those can reach up to 40x multipliers if needed without increasing BCLK.

RAM Memory Multiplier: This multiplier is directly affected by BCLK and results into a final memory speed. For example, if BCLK is running at 133MHz (stock speed), running a 2:10 memory multiplier should result into 666MHz for memory, which being Dual-Data-Rate based, results into 1333MHz. You'll have to keep an eye on this value or your memory kit will limit your CPU overclock while giving you head-aches trying to find which component is unstable.

CPU EIST & Speedstep: Properly used, this technology allows CPU frequency transition between low and high states. By changing CPU voltage and lowering CPU frequency, the CPU is able to consume less power at idle mode, while increasing values whenever any process is detected. Those features can be very useful if you want to overclock your PC while keeping low temperatures and power consumption at idle mode. Unluckily, many manufacturers disable these features when you start overclocking, letting CPU voltage/frequency at their max state all the time.

Turbo Boost: This feature is inherent to Core i5/Core i7 processors only. By monitoring which cores are processing information, Turbo Boost allows them to increase CPU multipliers individually for each core, increasing final speed by 1 to 4 multiples while the rest of the cores (unused) remain at stock speeds. It's best to disable this feature when overclocking since that will make easier the adventure to find your CPU's sweet spot. However, you can set a lower CPU frequency and let Turbo Boost reach your maximum tested overclock if you prefer.

Load-line Calibration: Also named as vDroop compensation or LLC, this feature increases CPU voltage to balance it between different states. At full load, CPU vCore droops to keep levels at Intel's specifications. While enabling LLC will give you the ability to run more MHz with "lower" voltage, this feature falls against Intel specifications, and it's not recommended, especially when you're aiming to increase vCore a lot.

PCI-E Frequency: Normally set at 100MHz, this value could help a little while overclocking your system and GPU. Try keeping it below 115MHz as it could produce S-ATA drives corruption. I normally set this value to 101MHz as a rule.

Voltage Values

If you're willing to sacrifice temperatures and power consumption to reach higher speeds, you must mess up with voltages. You need to be very careful with these values since you'll be adding extra heat and electron-migration to the components. Personally, I find better to reach maximum CPU frequency with stock voltage and let it stay there. That's because at that point, you'll be gaining speed while keeping your CPU cool enough. This will also increase power consumption by no more than 5-10 watts. Adding voltage can reach a point where CPU speed won't be comparable to the heat and power consumed, ending with lower efficiency results.

CPU vCore: This value is related to CPU frequency. If you want to get extra MHz, you'll need to add vCore to your CPU. CPU vCore is also 100% related to CPU temperature and final power consumption.

QPI/VTT/IMC Voltage: Increasing this value will be necessary when overclocking your BCLK and RAM frequency. It helps stabilizing RAM frequency, timings and QPI frequency too. If you're aiming for high BCLKs, you might need to increase QPI/VTT voltage. However, mid to high-end motherboards should be able to reach 200BCLK without increasing this value a lot (if needed).

VDIMM/DRAM Voltage: Related to RAM memory, you'll need to increase VDIMM voltage to achieve higher RAM frequencies. Contrary to CPU vCore, different RAM kits need different voltages and they might get to a point where adding voltage won't help anymore depending on the integrated circuits (ICs) built on your memory kit. VDIMM should be raised no more than 500 milli-Volts higher than QPI/VTT Voltage. Otherwise, you could permanently damage your CPU. Example: If your QPI/VTT voltage is set at 1.2 volts, VDIMM shouldn't be higher than 1.7 volts.

CPU PLL Voltage: You might need to increase this value when overclocking. Some people have found keeping this value at stock or even lower values helps achieving higher clocks. Don't over-volt this value a lot as it could quickly cause CPU degradation/damage. Leaving this in Auto-mode should be enough for 90% of our readers.

IOH Voltage: This value can help reach high BCLKs. Normally, letting it on Auto mode is enough.

ICH Voltage: It's best to set this on auto, as it powers the chip that keeps the communication from the CPU to peripherals.

How much voltage should I feed to my components?

Focusing on CPU vCore, the stock VID normally goes around 1.2 volts. If you're using stock cooling, you shouldn't go above 1.25 volts for 24/7 stability. In case you're using a high-end air-cooler or a water cooling system, then I'd recommend not going above 1.4 volts. In my tests, I used up to 1.5 volts to show you how little frequency vs. power consumption is gained from over-volting CPU with this range of values. Anyway, I don't recommend going above 1.4v unless you're using exotic/extreme cooling for benchmarking purposes.

About QPI/IMC/VTT voltage, it works around 1.1v-1.2v at stock conditions. This might be enough for low-medium overclocks, but higher values could be needed if you want to reach high BCLKs. Try keeping this below 1.5v in stock cooling. Also, remember this variable needs extra care to keep it in range with VDIMM Voltage as it was explained above.

VDIMM voltage is much more difficult to elaborate. Intel warns you not to pass above 1.65v, but people have proven going around 1.75v won't cause any damage to the CPU. Even that, I'd recommend not going above 1.65v, and if possible, try getting a low voltage memory kit (1.2-1.3v) as this removes stress from the Integrated Memory Controller. Unluckily, I can't tell you which voltage you should use for your memory kit since all of them are different and it all depends on which Integrated Circuit they are manufactured with.

Now that we've learned basic variables and how do they affect our overclock results, let's have a look at our testing methodology.



# Wow!fr0hzn 2010-08-25 05:00
I just bought an i5 recently and I have to say that I will definately try to overclock it, after I've read here what I can achieve :)
Very informative, thank you!
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# Glad to help.Servando Silva 2010-08-25 17:18
That's great. Post your questions/results in our forums!
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# Great InformationGorham4 2010-08-25 07:48
Very nice article full of great basic information. For those interested there are numerous groups that hold overclocking competitions. If you do a google on Forum Wars it will lead you to some interesting forums where you can gain additional knowledge and try you hand at basic and advanced overclocking with supportive groups.

Again thanks for a great article on what should be every computer owner's for activity when buying or building a new computer.
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# Nice work, but would have been great with benefits (or not)baldheadeddork 2010-08-26 16:59
Really nice comparison between the dual and quad core i-Series, but what's the payoff in applications? If you can make a second part showing these three in game performance and media encoding - that would bring it home.

It would also be interesting to see how the dual cores compare to the quads.
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# RE: Intel Core-i3/i5/i7 LGA1156 Overclocking GuideServando Silva 2010-08-26 17:39
As I've said in the article, I was focusing on how to overclock and variables involved. Perhaps, this review could help you make a decision:
I'll consider doing a second part focusing on performance though...
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# Very helpful guide!ulsar 2010-10-08 11:20
Great article for those newbies (and not so newbies) in this matter, like myself. I've got an i5 750 on a P7P55D EVO for about two months and it's time to enhance its performance a bit, so this guide will be really helpful.

Thanks a lot!
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# p55-usb3christian 2011-12-20 04:55
hi, i have p55-usb3 motherbord, but the same fan and a i7-860 cpu, i hope can use this great article anyway?
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# i3 330MChristian Conefery 2011-12-26 17:08
Is This possible with i3 330M or is it not powerful enough
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