BClk-based Overclocking Returns with Haswell?
 

With Intel's 2011-launched Core "Sandy Bridge" processors, Intel CPU overclocking as we know it changed. No longer could you overclock the CPU by stepping up BClk (base clock), a frequency that processors use to time various components, including the effective clock speed, and in some cases, memory, and uncore. Sandy Bridge left consumers with only one effective way of overclocking, stepping up an unlocked BClk multiplier, a feature only available with a handful expensive models.

According to a Hardcoreware report, when Intel took up the "one BClk to rule them all" approach with Sandy Bridge, it may have overlooked the possibility of the integrated GPU waking other components up from lower power states to use the L3 cache, affecting the chip's overall energy efficiency, which carried on to successive Core "Ivy Bridge" silicon. "Haswell" may present Intel with an opportunity to split core and uncore from sharing the same base clock, and as such it could be possible to crank up CPU clock speeds using BClk, without destabilizing the uncore. The author admits this is speculation on his part, but quite likely.

http://www.techpowerup.com/178739/BC...-Haswell-.html