Understanding how Exif and ifd0 data relate

Hey team,

I'm trying to get a sense of how the various data formats bundled with the Exif module relate. While a simple Google search provides me with more than enough information about the Exif format, i really haven't found anything helpful or in any way explanatory concerning the ifd0 format.

There appears to be a significant amount of crossover between the two formats—as well as with the "computed," "thumbnail" and "interop" formats, for that matter)—but how they differ or what unique purposes they serve, i can't tell. Does anyone have any helpful links they might share? Or just some brief insight?

Thanks for any and all help.