KF8 vs. MOBI7
To achieve the rich formatting in the Kindle eBooks it creates, Vellum makes use of a Kindle format known as KF8. The KF8 format, introduced in 2012, succeeds the older MOBI7 format and allows for features like drop caps, ornaments, and custom fonts.
These images demonstrate the same book with KF8 and MOBI7 formatting:
The mobi file generated by Vellum contains both KF8 and MOBI7 formatting. In most cases, readers will see the KF8 version. Unfortunately, there are still some places where Amazon continues to use MOBI7:
Amazon’s Look Inside
When the Look Inside for your book is initially created, Amazon may use the older MOBI7 format.
Early Kindle Devices
Some of Amazon’s oldest Kindles do not support the KF8 format. These Kindles include:
All other Kindle readers — the Kindle Keyboard, Kindle Touch, Kindle Paperwhite, and all Kindle Fire models — support KF8.
Amazon’s Kindle Previewer app includes an option for previewing as a Kindle DX. With this option, you can see the MOBI7 version of your eBook.
Amazon’s Cloud Reader
Amazon’s web-based Cloud Reader still uses the MOBI7 format.
Files Directly Loaded into the iOS Kindle App
Despite the fact that the Kindle app for iOS can display KF8 formatting, a mobi that is directly loaded into the app will instead be displayed using MOBI7.
To directly load a mobi file and see the KF8 formatting, you must first convert it to another format, following this set of instructions.
This only affects mobi files that are loaded directly. eBooks purchased and downloaded from Amazon will be displayed using KF8 formatting in the Kindle app for iOS.