Intel's Sandy Bridge CPUs cannot be overclocked except for model K CPUs which fall on the higher end of the price spectrum.
CPU speed is determined by two factors: the base clock and the clock multiplier. Sandy Bridge architecture doesn't allow the clock multiplier to be changed once it is set by the factory. The base clock however can be changed by the motherboard, but it would affect other resources such as the PCI bus and storage controllers which would make the system unstable.
The architecture of Sandy Bridge's successor, Skylake, did decoupled the CPU base clock speed from that of other resources on the motherboard. This means that motherboard manufacturers may allow Skylake CPU overclocking by giving users the option to alter the base clock.
Asrock told TechSpot that the next BIOS update for its Z170 motherboards will give users the ability to overclock non-K Skylake-S CPUs by altering the base clock. Supported CPUs include: Pentium G4400, G4500, G4520, Core i3-6100, i3-6300, i3-6320, Core i5-6400, i5-6500, i5-6600 and Core i7-6700.
Asrock noted that integrated GPU must be disabled if the CPU is overclocked by altering the base clock. This shouldn't be an issue though for most overclockers.
