Our first AMD SB750 equipped motherboard arrived this weekend courtesy of
Foxconn. We have been working around the clock to dispel or verify the rumors about how a simple update to the SB700 SouthBridge could unlock the overclocking potential of the Phenom processor series. It turns out changes to the SB750 are actually significant and include a new low level link interface that AMD has named Advanced Clock Calibration. Along with the new ACC technology is a significant update to the AMD Overdrive Utility and required BIOS code changes for this new interface to operate properly.
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Source: Anandtech