Jump right to the iMac Xray (direct link). So much to see here.

• Start off with that huge Apple logo (upper middle)
• Then move down to see two coin cell batteries (presumably to back up the NVRAM)
• The real mystery is those two massive rectangles on either side

Those rectangles appear to be acoustic chambers for the speakers. Interesting that they are different in shape, though the sound, no doubt, is perfectly symmetrical. Apple has some genius acoustic engineers.

Lots more detail in the post itself. Love teardowns.