5. Maximum Possible Power Consumption, Thermal Design Power (TDP) And Powernow

Why do we speak about "maximum possible" values for power consumption? First, it's normal to observe a range of values for the parameters or capabilities measured for finished CPUs from the same production run. Consequently, this means that when identical CPUs from the same production run are tested for maximum power consumption, some may consume a little bit more or less than others. Second, AMD and Intel communicate CPU thermal design power specifications. This value serves notebook developers as a design aid, and also provides a metric to help understand the computing power that leads to creating an outer limit when designing notebook cooling systems to match. The TDP also doesn't necessarily mean that a specific CPU model will consume that much current in real usage scenarios.

In addition, all Turion 64 models incorporate AMD's Powernow technology. Its principles are simple are well-understood from the Mobile Athlon 64 and AMD's desktop CPUs - in the latter case, AMD calls this techniques "Cool and Quiet." Whenever a PC system is working it never requires maximum processor performance at all times. That is why it's appropriate to manage clock rates and input voltages in narrow ranges associated with specific processor demands. This helps conserve current and lengthens battery life. Lowering power consumption and clock rates produces less waste heat when a processor is running in idle mode, so it's smart to design this kind of capability into a notebook. The same, of course, is true for desktop PCs as well.

When more computing performance is needed, power levels are increased automatically first, followed closely by jumps in the processor clock rate. If performance demands fall back, both values are likewise reduced and the power intake of the processor substantially diminished. This handling is broken into discrete performance steps for the Turion 64 known as "P-States." Every P-State may be described in terms of a specific combination of input voltage and clock rate. The Turion's power intake and thus also, its DC current demand, relate to CPU utilization and vary from model to model in a range of values from 7.9 to 32 watts.

This behavior is managed by default power values through user settings (see below), and is completely automatic without input from the operating system or the BIOS: the operating system ignores the processor's continuous utilization and has to communicate with the processor through a driver, to stay apprised of current clock rate and voltage settings.

Users have indirect influence over the CPU's power conditions and battery use through their selection of power settings.

The following tables compile all possible P-States for all Turion 64 models. The reports on power consumption clearly show that a statement like "the Turion 64 ML-40's power consumption is 35 watts" is both false and imprecise.

Without going into more detail about Intel's Pentium M CPUs and their energy saving Enhanced Speedstep technology at this point, which works much like AMD's Powernow, it is important to note that for Pentium M models with a 2 MB L2 cache and 533 front side bus and Dothan core, the TDP is rated at 27 watts. Where theoretical maximum possible power consumption is concerned, however, the Turion 64 MT-xx models have definite advantages based on their circuitry. Consider that the memory controller in the Turion is integrated within the processor die and already includes its current use in its TDP, and you can more easily appreciate that the AMD mobile processor's overall energy demand looks better than you might have thought.

On Intel platforms, the RAM controller is part of the Memory Controller Hub, usually abbreviated MCH, because it's available both with and without an integrated graphics core, as the 915GM and 916PM models illustrate. The power draw of the memory interface is thus not included in the TDP for an Intel CPU.