Intel locking down CPU Overclocking on Haswell
Intel's K-series processors offer fully unlocked multipliers that place few restrictions on overclocking. With Sandy Bridge and its Ivy Bridge successor, Intel has also allowed limited overclocking on regular Core i5/i7 CPUs that aren't part of the K series. On those regular-model chips, one may increase the maximum Turbo multipliers by four "bins" above stock, effectively delivering up to a 400MHz overclock. That boost won't get you into the near-5GHz territory attainable with fully unlocked versions, but it's a nice freebie that most CPUs and coolers can tolerate.
When we were discussing Haswell overclocking on this week's podcast, we weren't sure whether Intel had extended limited multiplier control to non-K Haswell products. We checked with the firm and are sad to report that this feature has been removed.
As a result, with Haswell, overclocking support is now almost entirely confined to K-series CPUs.