Rumors of the new AMD southbridge SB750 appeared back in April. Most interestingly they spoke of major improvements in the overclocking department although not how this would be achieved. It was later revealed that there were unused pins that would come to use with AMD's coming southbridges, the first being SB750. The secret is an updated version of the Advanced Clock Calibration, something AMD introduced with the SB700 chipset in favor of HyperFlash.
Motherboards equipped with the SB750 chipset has a new layout and sports a six-pin connection directly to the AM2+ CPU socket. These are the six pins that had been dormant. They makes it possible for the southbridge to override some of the processor's internal settings and thus increase the overclocking potential.
There is no impact on performance, no change of voltages or frequencies, it just allows for more and higher overclocking. Anandtech reports that the new BIOS of coming motherboards with the SB750 southbridge has a much wider range of settings for the Advanced Clock Calibration (ACC). In the past this function could be set in increments of 1 between -2 up to 0. With the board they've used they could set ACC to anything between -12 to +12. Negative values unlocks lower power operations while higher values unlocks better overclocking.
Exactly what it does hasn't been revealed, but it somehow seems to loosen the strains a bit and allow the cores to be pushed further in either direction. It should be emphasized that this is a Phenom-exclusive feature. You will not gain anything with your Athlon series processors. We should also mention that AMD will use this feature with its coming 45nm processors, which means that the prior reports of decent overclocking with the Deneb core, may be understated.
From the article:
"Our test results confirm AMD's statements that a 100MHz to 300MHz improvement in Phenom core speeds are attainable with ACC. This is not a guarantee and some processors will require significantly more tuning than others to get up to speed, but overall our experiences to date with several processors are very positive. Our otherwise clock challenged 9850BE suddenly started acting like a Tour de France rider on steroids with ACC enabled. Our clock improvements ranged from 200MHz to 410MHz depending upon our settings. What was particularly interesting is the fact that our largest improvements occurred when we tried raising HT ref clock and increasing the multiplier at the same time."
Advanced Clock Calibration is a software tweak today, and while Anandtech is able to prove that it does indeed work, you need the SB750 southbridge, a compatible BIOS and software with support for this to really be able to enjoy higher frequencies. All of this is supplied by AMD, and the reason for unlocking these higher frequencies, even though it seems to come at the cost of some settings being loosened, is that Intel is able to go so much higher than AMD's current processors. There have been talks of implementing this feature directly into the hardware, but so far it's all talk.
:: AMD's SB750: Enabling Higher Phenom Overclocks?
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