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Lynnfield’s Secret Weapon: Turbo Mode

One of the most interesting innovations introduced in Nehalem processors is the special Power Control Unit (PCU) that can control and manage the power consumption of individual processor cores.  Due to PCU Intel Core i7 processors got Turbo Mode technology that delivers dynamic and automatic CPU overclocking. I would like to remind you the idea behind this technology: when the processor is not fully utilized and its power consumption is far from threshold values the CPU raises its clock multiplier beyond the nominal setting. This technology becomes especially useful when the CPU workload is not clearly multi-threaded.

Core i7-900 processors could increase their multiplier by 1x and with an actively utilized single core – by 2x. As a result, the frequency of these processors was often 133 or 266 MHz above the nominal value. Of course, this is not a significant frequency increase, but even thanks to it alone the average performance of LGA1366 platforms with activated Turbo Mode was 3-5% higher than the performance of similar systems working without this technology enabled. In other words, Turbo Mode technology worked very well in Core i7-900 and proved absolutely worthy there.

That is why Lynnfield processors continued on with this technology. Its working principles remained the same, but new processors got the opportunity to manage their clock frequency in an even more aggressive manner. The multiplier in the new CPUs can be increased by up to 5x, which means that in favorable conditions the Core i7-800 and Core i5-700 clock frequencies may increase by 667 MHz over the nominal values, and this is a pretty significant increase I should say. However, it is important to understand that the actual frequency gain can only be determined taking into account the current CPU utilization and its power consumption. For example, the multiplier can be increased by 5x only if one processor core is loaded with work. If two or three cores of the four are utilized, then the multiplier can only be increased by 4x. But even if all four processors cores are loaded with work at the time, the clock frequency multiplier can be increased by 2x or 1x.

You can get a better idea of Lynnfield frequencies with enabled Turbo Mode technology from the following table:

There is one very important conclusion that we can draw here. When the CPU load is not multi-threaded or lightly-threaded, Core i7-800 and Core i5-700 processors may be faster than their predecessors from the top Core i7-900 series, because they can overclock themselves way greater in this case.

And we are not implying some ephemeral frequency increase here. In fact, most mainboards can switch the CPU into Turbo Mode permanently, so that the clock frequency will increase to its maximum irrespective of the current power consumption. Therefore, with Turbo Mode enabled the users will most likely see the following (to illustrate what we have just said we would like to provide screenshots taken off the system on Core i7-870 processor with 2.93 GHz nominal frequency):

  • The CPU is in idle mode. Due to Enhanced Intel SpeedStep power-saving technology its frequency is lowered to the minimal value of 1.2 GHz.

  • Single-threaded load allows increasing the CPU frequency to its maximum – 3.6 GHz, which is 667 MHz higher than the nominal value.

  • During two-threaded load the CPU frequency is increased by 533 MHz to 3.46 GHz.

  • Four-threaded load also allows the CPU to run fine at 3.46 GHz.

  • Under full load of eight computational threads the CPU frequency is set at 3.2 GHz, which is still 266 MHz higher than the nominal frequency.

Not only the frequency screenshots look impressive. To estimate the real benefit from Turbo Mode we compared the performance of the Core i7-870 based system with Turbo Mode and without it.

The average improvement from enabling the new second version of this technology makes about 8%. This gain can be even higher in applications that are not very well optimized for systems with multi-core processors. As a result, Turbo Mode looks an excellent trump of the new LGA1156 platform making it even more attractive for the user. Due to this technology Intel helps those software developers who haven’t yet got to optimizing their applications for multi-threading concept. New Core i7-800 and Core i5-700 processors, which are in fact real quad-core CPUs, may turn into high-speed pseudo dual-core or pseudo single-core solutions if necessary. And it is especially nice that this transformation happens in the background and doesn’t require any actions on the user’s part.

 
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