14 DAY TRIAL // Last week AMD issued two whitepapers that were supposed to cast some light over the K10 series thermal design power. However, the figures included in these whitepapers raised serious questions and AMD hasted to dignify the users with an answer.
Some time ago, both Intel and AMD were using the same values for expressing the Thermal Design Power. This value, when referred to microprocessors, represents the amount of power the cooler has to dissipate in order to preserve the CPU's unaltered functionality.
Starting the K10 architecture, AMD can not afford to use the same standard measurements due to engineering reasons. While Intel's architecture allows the CPU to go beyond its specified TDP for a short interval, AMD's K10 design can not do this and the producer has to release the conservative TDP ratings.
The Phenom family shows an increase in the thermal design power for the new K10 processor series. The Barcelonas are exactly in the same situation, since they share almost any major specifications (including the TLB erratum, as it seems). Brent Kerby, the unfortunate author of both whitepapers explains that the inconsistency is the result of timing and the very nature of ACP itself. "The measured value of ACP already included the changed TDP values", he states.
According to the same source, the algorithm for calculating the Average CPU Power is not affected by the 21 percent difference between the two published whitepapers. "When we published the first whitepaper, we had to anticipate TDP changes", adds Kerby. The last issued document should be replaced with the TDP changes from the second.
The ACP specific margins are alleged to be an integral part of the ACP and Kerby mentions in his whitepaper that "The results across the suite of workloads are used to derive the ACP number. The ACP value for each processor power band is representative of the geometric mean for the entire suite of benchmark applications plus a margin based on AMD historical manufacturing experience."
Therefore, if the processor's TDP were to go up again, the ACP values will have to undergo revisioning again, but AMD refused to comment upon further increases in the TDP value.