L O S T C I R C U I T S

Minireview

In a world increasingly ruled by energy and greenhouse effect concerns, power consumption of electronics is becoming an important factor in the overall acceptance of the product. Clearly, an 800W audio system will not be expected to draw a meek 50W but a component as small and humble as the processor in a personal computer is. This is where AMD's current desktop flagship CPU, also known as the Deneb core-based Phenom II X4 965 Black Edition has taken quite a bit of flak over the past few months. Whereas every other AMD processor is rated at or below 125W TDP, the '965 Black Edition with its unlocked multipliers for core and North Bridge has been rated at 140W, enough to raise more than one eyebrow in the evermore energy conscious world. From a misconceptual point of view, the biggest issue is that TDP does not mean that the processor will actually draw that much power, rather the TDP acronym has undergone so many permutations that it is no longer really clear what it stands for. To sync everybody back to the same page, it is the thermal design power, that is the power requirement that has to be met by the voltage regulator module and the heatsink in order to warrant save operation of the CPU under any and all conditions - as long as they are reasonable.

With the samples we had in our test labs, we never got even close to the 140W, in fact, we struggled to hit the 110W benchmark even if power was measured before the VRM which, given an efficacy in the order of 75-80% translates into maximum CPU power in the area of some 90W. It is self-understood that there have to be margins, especially when dealing with Taiwanese or Chinese motherboard manufacturers, at the same time, that 140W number has made the rounds and not helped AMD's reputation for power efficiency.

Reason enough to introduce a new revision of the Phenom II with a few small but nonetheless important differences under the metal layers.

In a nutshell, there are four things that differentiate the new C3 revision from the older Rev. 2 silicon:

• The revision: We already covered that, it is now C3
• TDP: The new C3 Revision has a TDP of 125W
• Overclocking headroom: The C3 Revision has noticeably more overclocking headroom than its predecessors
• Implementation of power and C states: The previous revisions implemented p- and c-states in the BIOS and the execution of the different states was done using the South Bridge as control instance. Some of these hops were among the reasons for the switching lags causing the "CnQ Performance Hit". The C3 Revision implements C and P states in hardware, specifically, the additional PMU logic was added to the existing design, allowing for much faster transitioning between the different states.
• Return to individual Core Clock Gating: Because of the lag in transitioning from one p-state to another and the performance hit associated with threads hopping from a high clock frequency core to a low frequency core, AMD had disabled clock gating on a "per core" basis in the last several BIOS revisions. The hardware-based PMU and its faster switching allows to return to this feature without taking too much of a performance hit.

We'll take a look at the details on the next pages.