Overclocking Intel's Core i5 750

Manufacturer: Intel

While still quite expensive right now, there's no doubt of the performance potential Intel's Core i5-750 brings to a market where the extremely popular Core 2 Quad products once ruled. Once the price of DDR3, motherboards and the CPU drops a little, in addition to having more performance CPU coolers with an LGA1156 bracket, we're sure we'll see a large uptake similar to the insanely popular Q6600 G0.

Last year we did an overclocking guide for the Core i7-920 which still proves popular, so we're also committing our accumulated knowledge in explaining to our readers how to get the best from the current crop of LGA1156 P55 motherboards: from inexpensive £100 options to £200 behemoths; we cover the BIOS settings that will make maximising your i5-750 overclock possible.

Obviously as time goes on BIOS versions change, potentially including or even removing options that you see here. Also remember that your mileage will vary according to CPU quality, cooling environment, power supply quality (both from the wall and the PSU unit) and other hardware in the system, so the voltages and settings recommended are to be used as a general guide only.

If you're looking for performance results, check out our initial review of the Lynnfield CPUs that includes overclocking performance data.

Overclocking Intel's Core i5 750

What to look for?

For the most part the core changes are the same across the different motherboard manufacturers, these include:

Base Clock: Just like the LGA1366 Core i7 range, and as a replacement for the old Front Side Bus clock on Core 2 and Pentium products, the base clock is the underlying frequency that changes all of the CPUs clock domains, not just the core clocks.

The standard frequency for the Core i5-750 is 133MHz. Increasing this affects the core frequency, CPU-northbridge frequency and QPI frequency - your CPU may be limited by the latter factors that do not have the availability of voltage increments to compensate, although increasing the frequency of the CPU-NB clock does directly increase memory performance (especially memory write speeds).

Intel TurboBoost: This is Intel's auto-overclocking feature that increases the CPU multiplier beyond its stock value when fewer than all four cores are being used. TurboBoost has two levels of multiplier increment, which for the i5-750 are 21x and 22x. On some boards the 21x multiplier can be forced on permanently, however whether this actually "holds" is dependent on the BIOS and board. Gigabyte claim it's impossible, however we've certainly seen it work with the MSI P55 GD65. When overclocking it's typical to turn this function off.

CPU Multiplier: Like we said above, some boards allow the 21x multiplier which makes hitting above 4GHz much easier, however since all the boards with an i5-750 will have the 20x multiplier, a nice, round 4GHz with a 200MHz baseclock should easily be achieved. A word of advice from the OC community though: Uneven multipliers typically overclock the CPU better.

Intel SpeedStep/C1E/Power Saving Technology: This underclocks the multiplier when the CPU is idle to save power, however it can also affect performance sometimes, especially SATA throughput as we've seen in a few cases. Considering we're going to be aiming to heavily overvolt to achieve high clock frequencies, saving power is not the greatest concern, so this can be disabled.

DRAM Frequency: Core i5-750 CPUs have one less memory multiplier available than the Core i7 LGA1156 products. The memory clock is reliant on the base clock, and there's still 6x, 8x and 10x multipliers available allowing a 2GHz DDR3 clock at 200MHz base clock, or, a more usual 1,600MHz with the 8x multiplier. Better motherboards will show the total frequency as the base clock changes in the BIOS so be wary of what memory is in your motherboard, and try not to run it much faster than it can handle. If you need to drop a memory multiplier, offset the loss of bandwidth by dropping the memory timings as much as possible.

DRAM Channel Timings: Intel allows mixed modules in each memory channel, so the timings can be set separately in most BIOS'. For our needs though, it's best to have matched modules. Some motherboards don't include the option to change both memory channels at once so make sure you change the timings which relate to the channel your memory is plugged into, or, if you're using all four slots (both channels) that the settings are uniform across them both, which can sometimes mean setting everything twice.

QPI Frequency: Anything over 150-160MHz base clock, select the lower multiplier. It does not affect performance, but it is also connected to the base clock and will potentially limit the total overclock.

PCI-Express Frequency: Unlike other chipsets, no additional voltage can be applied to the PCI-Express core specifically, however there is sometimes a PCI-Express clock signal amplitude which will substitutes for this. Increasing the clock heavily can certainly give some additional performance in multi-GPU scenarios to make up for the fact it only offers two lanes of x8 bandwidth PCI-Express 2.0. It also depends heavily on the quality of graphics card.

We've read this option is also directly linked to the SATA frequency - whether by the same clock generator, or perhaps the DMI link to P55 is overclocked? We don't specifically know yet, but increasing the SATA frequency can potentially cause data corruption, so be mindful of this.

Why would you ever overclock the PCI-Express then? Well MSI claims it has a positive effect on base clock overclocking, however since all boards should do 200 without fussing over it, we don't see the need to change it unless you're overclocking very heavily.

CPU Clock Amplitude: We typically increase this slightly, however it can't just be maxed all the way because that can lead to just as many potential problems of clock signal overshoot, depending on the quality of motherboard, its physical traces, the size of the clock data eye and possibly even electromagnetic interference.

Load Line Calibration: This factor is a compensator for voltage drop/droop as the CPU goes from idle to load. We recommend enabling this where possible, although some boards offer different levels offer a percentage change, which can require more research to know the specific factors.

CPU Voltage: This is often given as either an offset or absolute voltages, depending on the motherboard. Personally we prefer absolute voltages for a heavy overclock, but for a "light" mid-3GHz overclock an offset of up to +300mV will do. Even stock voltages will go quite far with a good CPU. For a heavy 4GHz overclock ~1.38 to 1.425V is normal, and above 4GHz usually the recommendation from motherboard vendors is anything from 1.45V-1.5V. That is certainly getting dangerous for long term use rather than just benchmarking, and it's very difficult to keep cool. Of course, your mileage will vary mostly on this factor so as a rule of thumb start aim for the least voltage you can get away with.
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