EPUB vs AZW3

Hello,

From the "inside" (i.e. from within an editor) AZW3 ebooks look very similar to EPUBs. Same code, same files, more or less. EPUBs have a "content.opf" file, whereas the one in the AZW3 is called "metadata.opf", but they are very similar too.

So what are differences between the two? What does a converter do? I know that simply changing the extension won't work, but it doesn't seem to be much more complicated.

I got a feeling the answer might be very technical, but I'm willing to study :)

Thanks,

i