The Intel® Core i7-3517U processor’s normal clock speed is 1.9 GHz. The maximum Turbo boost frequency is 3.0GHz.
Please note that Intel® Turbo boost is engaged automatically depending on processor’s load, voltage, power and temperature. Therefore, at a particular moment the processor may reach 2.5 Ghz or 2.9 GHz depending on those variables. Usually this feature comes enabled in BIOS by default.
Intel® Turbo Boost Technology—On-Demand Processor Performance
I hope this answers your question.