Articles: CPU

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When Intel launched their Sandy Bridge processors and new LGA1155 platform, the overclocking procedure changed. The traditional formula where CPU frequency is derived as “clock generator frequency times clock frequency multiplier” lost one of its unknown quantities. Intel tied together the base generator frequency and all bus and controller frequencies in their new chipsets. As a result, it became almost virtually impossible to play around with the base clock.

LGA1155 platform uses BCLK frequency of 100 MHz. Intel P67 based mainboards have everything necessary to adjust this frequency within a very large interval. But the highest BCLK frequency can go without threatening the system stability is about 105 MHz. So, the best overclocking you can achieve with traditional means is only 5%.

Ridiculous, isn’t it? Indeed, so Intel made sure that there was a different approach. There are a few modifications in the LGA1155 processors line-up that have an unlocked multiplier: Core i5-2500K and Core i7-2600K. The company manufactured processors like that for other platforms, too, but they used to be only a pricy toy for hardcore overclockers, who didn’t mind using extreme cooling solutions in their experiments. Today an unlocked multiplier is the only way to increase the CPU clock frequency substantially beyond the nominal values. Therefore, Core i5-2500K and Core i7-2600K are only $10-$20 more expensive than their ordinary brothers: today no one considers overclocking-friendly Sandy Bridge modifications to be luxury.

By replacing the BCLK overclocking with multiplier overclocking simplified the entire overclocking process altogether. Overclocking used to be a science that required thorough selection of the system parameters, setting correct voltages in different processor units and busses, which had a serious impact on the system stability. Now overclocking has become much more straightforward. By setting a higher frequency multiplier, you can only increase the resulting processor frequency, but cannot affect the performance of other system components. Therefore, you no longer have to monitor even the memory frequency during overclocking, as it remained constant. So, there is only one parameter overclocking success depends on: processor core voltage. All other voltages hardly influence the results.

The frequency potential of Sandy Bridge processors is impressive. The Core i5-2500K processor available in our lab overclocked easily to 4.2 MHz at default Vcore.

Additional core voltage increase to 1.4 V allowed reaching new heights: the system remained stable at 4.7 GHz.

The CPU core temperature during our stability tests didn’t exceed 80°C.

Note that we tested a Revision D processor, while the mass production units will be Revision D2, which should work stably at slightly higher frequencies.

Processor overclocking may be also accompanied by memory overclocking, which frequency can be set using an individual multiplier. Any LGA1155 processors including non-overclocker modifications, support memory frequencies from DDR3-1067 up to DDR3-2400 with a 266 MHz increment. All memory frequency multipliers are operational and we could easily get our test Core i5-2500K to clock the memory, for instance, as DDR3-2133.

But is memory overclocking the only thing the owners of regular processors that do not belong to the K-series can count on? Luckily, not: Intel allows limited adjustment of the frequency multiplier also by regular Sandy Bridge modifications. Although I wouldn’t pin up high hopes on this option: you can only increase the multiplier no more than four increments above the nominal.

This overclocking doesn’t affect Turbo Boost, so we can consider it a pretty acceptable option for undemanding users. For example, the frequency of a 3.1 GHz Core i5-2400 processor can be easily increased to 3.6 GHz (Turbo mode will provide additional 100 MHz), and when only one core is utilized, the clock frequency will rise up to 3.8 GHz.

Similarly, the frequency of the junior member of this family, Core i5-2300, can be overclocked to 3.3-3.5 GHz.

The advantage of this limited frequency increase is that it doesn’t require any voltage adjustment at all: everything works fine at the default voltages. Also, no special cooling is required either: a regular boxed CPU cooler will do just fine.

However, even this simple overclocking is not always available. Mainboards with integrated graphics built around Intel H67 chipset do not provide access to the processor clock multiplier or memory frequency multiplier.

Therefore, if you intend to use the integrated graphics in Sandy Bridge, forget about overclocking. At least, until Intel Z68 chipset comes out, as it will combine the features and functionality of P67 and H67 in one.

Although K-series processors cost just a little more than the regular models, we can’t help noticing that Intel has increased the “membership fee” for entering their overclocker club quite significantly. There are no processors with an unlocked multiplier in the sub-$200 price range and there are no plans to launch any so far. So, if you don’t want to give up the opportunity to overclock your Sandy Bridge processors on the LGA1155 platform, you will have to pay for Core i5-2500K or Core i7-2600K.

You may have heard something about an alleged chipset on Intel roadmap that should bring back to the LGA1155 platform traditional overclocking methods involving clock generator frequency increase. However, these are all rumors. The mythic Z68 will come out, but it will simply be an enhanced P67, which will provide access to processor multiplier adjustment.

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