Before I buy..

[SensualPoet]

Originally Posted by PeterT

The large difference is that of standards.

ePub IS an open format defined by the Open eBook Forum of the International Digital Publishing Forum

AZW - The Amazon proprietary format. This is very close to the MOBI format sometimes with and sometimes without DRM. The DRM is unique to the Amazon Kindle.

MOBI - MobiPocket format, usable with MobiPocket's own reading software on almost any PDA and Smartphones. Mobipocket's Windows PC software can convert .chm, .doc, .html, .ocf, .pdf, .rtf, and .txt files to this format

https://wiki.mobileread.com/wiki/E-book_formats has more info.

Worth noting perhaps is that kePub is the proprietary format of Kobo, very close to ePub, but does NOT require Adobe DRM as it supplies its own unique DRM.

And possibly one more ... the ePub DRM variant Nook uses which makes its books unreadable on other Kobos and Sony devices which otherwise share the ability to display Adobe DRM.