[HarryT]

You are confusing ebook formats with file extensions. Mobi is a format. KF8 is a format. AZW is merely a file extension. A file with a ".azw" extension can be either a Mobi or a KF8 book. It may, indeed, hold both formats in the same file.

KF8 is a very much richer format than Mobi, and can handle much more complex formatting, as well as supporting features like embedded fonts, which Mobi does not.