How does Intel Turbo Boost work?

Intel® Turbo Boost Technology 2.01 automatically allows processor cores to run faster than the rated operating frequency if they’re operating below power, current, and temperature specification limits. Frequency increases occur in increments of 133 MHz for Nehalem microarchitecture processors and 100 MHz for Sandy/Ivy Bridge microarchitecture processors. When any of the electrical or thermal limits are reached, the operating frequency automatically decreases in decrements of 133 MHz/100 MHz until the processor is again operating within its design limits. 3.5 Ghz in your case is the design limit at which processor can run continuously for long time given the standard cooling is working properly.

Availability and frequency upside of Intel Turbo Boost Technology 2.0 state depends upon a number of factors including, but not limited to the following:

• Type of workload
• Number of active cores
• Estimated current consumption
• Estimated power consumption
• Processor temperature

Intel Turbo Boost Technology 2.0 allows the processor to operate at a power level that is higher than its TDP configuration and data sheet specified power for short durations to maximize performance.

links :

• http://en.wikipedia.org/wiki/Intel_Turbo_Boost
• http://www.intel.com/content/www/us/en/architecture-and-technology/turbo-boost/turbo-boost-technology.html

Turbo boost raises the speed when the CPU is capable of it. Intel would love to guarantee you could run at 3.9GHz all the time, but they can't. The CPU might overheat or the current draw might be higher than the packaging can handle. So they guarantee you 3.5GHz and raise the clock to as much as 3.9GHz when they can.