Looks like the rumor mill was right to be buzzing about AMD incorporating a dynamic clock speed boosting mechanism similar to Intel's Turbo Boost into its upcoming six-core processors. AMD has confirmed to us that the chip code-named Thuban does indeed include such a feature, dubbed Turbo Core technology.
At its heart, Turbo Core is essentially similar to Intel's Turbo Boost. When not all of the processor's cores are fully occupied, this feature raises the clock speeds on active cores above the default frequency while staying within the CPU's defined thermal limits. However, Turbo Core is a little bit different from Intel's technology in its operation—and generally simpler.
The processor becomes eligible to enter the "boost" state when three or fewer cores are heavily occupied with work. This boost state is a simple, binary condition. When the CPU enters this state, the peak clock speed for the three affected cores will jump by as much as 500MHz above the baseline, improving performance. To give a possible example, a future Phenom II X6 CPU might have a base clock speed of 3.4GHz but range up to 3.9GHz when only one to three cores are busy. Meanwhile, the three inactive cores will be in an idle state, with greatly reduced power draw. Three cores is the magic number here because that's the split on six-core parts; three cores go into boost, and three do not. Quad-cores based on Thuban may have a 2/2 split.
Below is a quick diagram from AMD that will either clear up exactly how it all works or leave you in a state of deep confusion.
Unlike Intel's Turbo Boost, the Turbo Core mechanism doesn't establish multiple frequency thresholds based on the number of cores occupied or the present thermal conditions. For instance, there's no separate peak speed allowed when only a single core is busy, nor does Turbo Core rely on sophisticated real-time thermal monitoring. AMD will define the peak Turbo Core frequency for each CPU model, and the CPU's model will determine its behavior. All chips that bear a given model number will behave identically with regard to frequency. The particulars of the individual chip or the thermal environment won't influence how much time the CPU spends in a boost state.
This may be a less sophisticated approach than Intel's Turbo Boost—and perhaps not as likely to wring every possible bit of headroom out of a given thermal envelope—but AMD cites the deterministic behavior of its Turbo Core-endowed processors as a positive trait.
Turbo Core will act in concert with a host of other existing mechanisms to regulate clock speed and voltage, and that symphony is becoming increasingly complex. AMD tells us Cool'n'Quiet will still reduce clock speeds dynamically on cores that aren't busy, although we're unclear on whether AMD's decision to lock the P-states of all cores together on the Phenom II will remain in force here. The dynamic voltage scaling portion of Cool'n'Quiet still applies the same voltage across all cores, and Thuban does not include the ability to gate off power entirely to an idle core like Intel's Nehalem-derived CPUs. The upcoming Llano APU is slated to be the first AMD processor to employ power gates for individual cores.
Regardless of the finer points, Turbo Core should give AMD a credible answer to Intel's Turbo boost. That's true in part because of Thuban's other virtues, which aren't limited to dynamic clock speed increases. Thuban ought to have more thermal headroom available to it thanks to a process technology change. For this chip, GlobalFoundries has added a low-k dielectric to its high-performance 45-nm SOI fabrication process, which should reduce leakage power.
As a result, AMD expects Thuban's six cores to fit into established power envelopes while featuring base clock speeds similar to current quad-core Phenom IIs. In fact, the firm plans to introduce a Black Edition six-core Thuban processor at speeds "over 3GHz, substantially," so the example we cited above may not be far from the truth. That part will gain 500MHz from going into a boost state, which means effective clock speeds with lightly multithreaded applications could approach or exceed 4GHz. Lower-end Thuban derivatives will get smaller frequency bumps out of Turbo Core, and AMD intends to offer a range of Thuban-based products in its current suite of power envelopes.
Those processors will see their formal introduction in the coming weeks, almost surely under the Phenom II X6 brand name, and they should be drop-in compatible—Turbo Core and all—with existing Socket AM2+ and AM3 motherboards. Although the move to six cores and the addition of Turbo Core may not be enough to wrest the performance crown from Intel's 32nm Gulftown-based Core i7-980X monster, AMD anticipates that the new Phenoms will offer an attractive price-performance proposition, in keeping with its recent tradition.