Microprocessors
If not stated otherwise, the watts dissipated refers to the peak-value thermal design power for a whole processor family. Since thermal design power relates to the potential maximum thermally significant power used by the most energy using member of a processor family, it is not useful for comparing processors within a particular family. It is also not useful for comparison of the energy efficiency of individual processors in different families, because it relates to the family, not the individual CPU. Thermal design power is defined differently by different manufacturers, so it is not comparable between manufacturers.
Different architectures vary in how many operations they perform per clock cycle, so MHz/W values are not useful for comparing processors using different internal structure (see Megahertz myth). Since TDP is defined for families, not individual processors, MHz/TDP W are not useful for comparing processors using the same internal structure.
For measures of energy efficiency in computing, see Performance per watt.
Read more about this topic: List Of CPU Power Dissipation Figures