[goodcanadian]

As stated in the wikipedia article, the microwaves penetrate to a depth of about 1cm (give or take, depending on the food). So, in a sense, it can be argued that the microwaves heat from inside, though in reality, not very far inside.

The trouble is that microwaves work mostly by heating liquid water. Ice is not liquid water and absorbs microwaves relatively poorly. The already melted parts tend to heat up faster while the still frozen parts heat up very little. This, in addition to the limited penetration, is how you wind up with food that is napalm hot on the outside and still frozen in the middle. If you are trying to defrost something or cook it from frozen, you are much better off using a lower power setting. The peak power output is actually the same, but it gets turned on and off (you can hear it cycling) so that the warm areas of the food have more time to transfer some of that heat to the still cold areas through good old fashioned conduction. Incidentally, this is the same reason that the instructions for many pre-made items tell you to let them sit for 1 or 2 minutes before taking it out of the microwave.

[pmahoney]

(Some?) Panasonic microwaves claim to be able to lower microwave power linearly without the on/off power cycling. I'm mildly curious if their marketing claims of superior cooking hold up.

http://www.panasonic.com/in/consumer/home-appliances-learn/t...

[MrBuddyCasino]

Indeed, and they seem to make a difference: http://thesweethome.com/reviews/best-microwave/