As for the Core frequency, Intel added additional register bits for turbo multipliers increasing the theoretical maximum multiplier from 63x to 80x (!). The BCLK frequency steps are still the standard 100MHz and the voltage is programmable via the iVR (more on that later). Note that opening up the CPU ratio registry to 80x is not a guarantee that the CPUs have the capability of operation near to 80?100MHz. As Intel suggests, its engineers look for ways to give as much tools as possible for users to find the physical limits of their design and not be arbitrarily limited.
Regarding the BCLK frequency, we now have the same BCLK gear ratios at our disposal as on X79 but were not present on Ivy Bridge. In case you did not know about a year ago, I enquired Intel about the non-availability of this gear ratio on Ivy Bridge at a technology session at CeBIT 2012. Simply said, they explained that there was simply not enough time to add the gear ratios to the Ivy Bridge micro-architecture. It is not simply a matter of just ?adding the options?. The gear ratio requires an additional DB1200 clock multiplier on the CPU package ? not as simple as it sounds!
The gear ratios selection includes options 1.00x, 1.25x or 1.67x as BCLK ?multipliers?, giving you an offset of 100MHz, 125MHz or 167MHz. For those who wonder, the BCLK gear ratios seem to be fully functional with S3 sleep state enabled. This means your Haswell system is able to resume from S3 state when having the BCLK ratio overclocked. For those who wonder if Haswell supports the 2.50x gear ratio that was also available on the early X79 motherboards, the answer is yes and no. Yes, theoretically, it might be possible to use a 5:2 PEG/DMI ratio, which is the 2.50x BCLK gear ratio, but implementation depends on the motherboard vendor. We will find out when the products launch.
The range of BCLK overclocking, for each gear ratio, is still the same like on Ivy Bridge: about five to seven percent (5-7%). On Ivy Bridge, the highest BCLK frequency we have seen so far is 117MHz (+17%) and there is no reason to assume this will be worse on Haswell. So perhaps we might see 167MHz x 1.17 = 195MHz BCLK frequency?
Completely new for Haswell is gaining control over the Ring Bus frequency. In rough terms, you can see this ring bus frequency as the new ?uncore frequency? ? although that is technically not correct. The ring bus is adjustable up to 80x ratio as well, just like the CPU, and is typically not clocked higher than the CPU core frequency. As Intel stated at IDF 2013 Beijing, they have not seen much performance increase from overclocking the ring bus frequency, but did hint at the possibility of the ring bus frequency affecting overall system stability. It will be interesting to see what overclockers (read: you!) will come up with in this respect.
As we know, Ivy Bridge featured a reasonable mediocre memory overclocking. That is, if we compare it to the AMD record-breaking memory overclocking capabilities. The DRAM frequency overclocking seems to have improved on the new Haswell CPUs as Intel is now officially supporting logic all the way up to DDR3-2933. Although a bunch of Z77 motherboards currently already supports the DDR3-2933 ratio, it is not official Intel specification. Having this ratio supported by Intel is in fact a step forward as it means running it passed the Intel internal validation and qualification at this rated speed. Nice!
Last but not in the least important, the IGP clock frequency is also still unlocked. Intel provides up to 60x ratio, in 50MHz steps. This means a theoretical maximum overclock of 3GHz core frequency. Given the GT2 of Ivy Bridge can currently reach about 2GHz under extreme cooling; we do not expect the more complex GT3e to reach that 3GHz, but who knows? Overclocking has never been an exact science.
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Originally Posted by G0ldBr1ck
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