How Intel Turbo Boost Works


Normally the computer processor in your laptop or desktop has a standard clock speed which partially determines how quickly it performs. While the processor might lower its clock speed at times in order to conserve power, the clock speed which is stated when you buy the computer is the fastest clock speed you’ll receive unless you decide to overclock.

If you do decide to overclock, or you ever speak to someone who regularly overclocks processors, you’ll discover a dirty little secret – the clock speed a processor ships at is typically much lower than the actual maximum clock speed which the processor could achieve.

The extra headroom isn’t used only because the manufacturer (Intel or AMD) needs to plan for worst case scenarios, which means they need a processor which is sold as a 3GHz processor to work at that speed even if someone decides to use a winter jacket as a PC case.

At least, that is how processors used to be. However, Intel’s new Core i5 and Core i7 processors have a feature called Turbo Boost which has the ability to dynamically scale up the clock speed of a processor depending on the thermal headroom available.

How Intel Turbo Boost Works
Intel Turbo Boost monitors the current usage of a Core i5 or i7 processor to determine how close the processor is to the maximum thermal design power, or TDP. The TDP is the maximum amount of power the processor is supposed to use. If the Core i5 or i7 processor sees that it is operating well within limits, Turbo Boost kicks in.

Turbo Boost is a dynamic feature. There is no set-in-stone speed which the Core i5 or i7 processor will reach when in Turbo Boost. Turbo Boost operates in 133Mhz increments and will scale up until it either reaches the maximum Turbo Boost allowed (which is determined by the model of processor) or the processor comes close to its maximum TDP. For example, the Core i5 750 has a base clock speed of 2.66GHz but has a maximum Turbo Boost speed of 3.2GHz.

However, Intel still advertises these processors by their base clock speed. This is because Intel does not guarantee that a processor will ever hit its maximum Turbo Boost speed. I have yet to hear of an Intel processor which can’t hit its maximum Turbo Boost speed, but hitting the maximum Turbo Boost is dependent on workload – it won’t happen all of the time.

Why Turbo Boost Rocks
Despite Turbo Boost’s lack of predictability, it is still an excellent feature. It provides a solution to the problem of compromising between dual and quad core processors.

Before Turbo Boost the choice of purchasing a dual core or quad core processor was a compromise. Dual core processors were clocked faster than quad core processors simply because having more cores increases power consumption and heat generation. Some programs, like games, favored dual core processors, while other programs, like 3D rendering software, favored quad cores. If you used both types of applications you had to make a choice about which was most important to you. You couldn’t receive maximum performance in both from a single processor.

Turbo Boost gets rid of this compromise. If you use the Core i5 750 in a 3D rendering application it will probably only operate at its base clock speed because all four cores will be used. However, if you use the Core i5 750 with a game which only needs two cores – presto! – the third and fourth cores go into a low power state and the two cores you’re actually using are running at a clock speed as fast as what you’d expect from a standard dual core processor.

The Future of Intel Turbo Boost (and AMD’s Response)
Turbo Boost is a great feature, and it is part of the reason why Intel’s latest processors are often superior to those from AMD. However, there is still more potential to be tapped. By the end of 2010 Intel will have released ultra-low voltage Core i5 and i7 processors for laptops. These processors will use Turbo Boost as a way of improving battery life.

For example, Intel will be releasing a processor called the Core i7 620UM. This processor has a base clock speed of only 1.06GHz. However, it has a maximum Turbo Boost of 2.133 GHz. What we will end up with is a processor which will run at only the base clock when on battery but can double its speed when plugged in.

Intel’s success with Turbo Boost has not gone unnoticed by AMD, however. With the release of the six-core AMD processors, such as the Phenom II X6 1090T, AMD has introduced a similar feature called Turbo Core. Turbo Core isn’t as advanced as Intel’s Turbo Boost, but it is a clear sign of the direction processors will be taking in the future.

It appears the days of set-in-stone processor clock speeds are over. The future will be about changing a processor’s performance on the fly to meet the demands of the user.

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