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but keep the numbers for the Atom correct (the 20W while idle are just wrong (for N270 + 945 GSE)).
While idle and in full power mode an N270 will draw far more than the 2W "Thermal Design Power" for the chip. The 945GSE is a nice Northbridge but, it is also not as low power as Intel's figures.
Embedded processors tend to be rated on their maximum power consumption - power supplies and regulators are very important to these systems so the amount of current needing to be pushed through each power rail has to be accounted for.
Intel processors are generally marketed to people who have a practically infinite supply of power - a 450W+ PSU or suchlike. They rate their chips on how good the *heatsink* has to be validated for to draw enough heat away for reliable operation. A 65W Intel processor will give off 65W of heat; the heatsink *must* quench this according to the TDP. It may draw closer to 90W though.
Check out Freescale's docs and when they say an MPC8610 draws 11W maximum at 1.3GHz, they mean that. It is also fairly indicative of system ratings as a whole - since the chips are so well integrated they can be placed on a board with little more than RAM to operate perfectly well (unlike Atom + 945GSE).
Intel's battery life is entirely reliant on dynamic voltage scaling and dynamic frequency scaling and clever standby modes, to the point that they have added newer and better processor sleep states in every major revision. ARM and PowerPC processors require much less work, but still implement (in certain revisions) some of these features - higher end ARM chips in particular will allow processor core voltage scaling and frequency changing, plus allow dynamic clocking of nearly every bus attached.