AZW3, Amazon KF8 eBook File (.azw3)
The AZW3 eBook file format
Amazon created the AZW3 format (Kindle Format 8, also known as KF8) to replace the older AZW version of their Kindle eBook files. Contrary to the outdated AZW files, files with the AZW3 extension support markup languages like HTML5 and CSS3. Additionally, it has more formatting options than the old AZW files. Thus, AZW3 is the only format newer eBooks are distributed in when purchasing them from Amazon.
Technical details of AZW3 files
Essentially, AZW3 files consist of compiled EPUB files which utilised a Palm database together with Amazon's DRM protection scheme. EPUB 3 versions support is targeted, yet already existing EPUB files can be used as well. In most cases, contained in the AZW3 file a MOBI file can be found in the beginning, wile the newer EPUB (KF8) can be found later in the file. It is supported by fourth-generation Kindle devices (version 4.1.0), and the Kindle Fire device.