A MOBI extension file is an electronic book saved in the MOBI format, a
format originally used by the Mobipocket Reader but now supported by a
number of different readers.
Mobipocket Reader was developed by Mobipocket SA, which was a French
company that also created the MOBI e-book file format for mobile phones,
personal digital assistants, and desktop operating systems.
The MOBI file contains an electronic book and may incorporate copyright
protection to prevent unauthorized copying or viewing.
MOBI files are compatible with various eReaders, tablets, PDAs, and
desktop computing applications.
Amazon now owns the MOBI format, which means that Amazon’s e-book
formats, including AZW, AZW1, and AZW3, use the MOBI format but
incorporate a proprietary DRM scheme.
It should be noted that Amazon’s new Kindle Format 8 (KF8) is based on
the MOBI format.
MOBI and KF8 support many new formatting and layout options, including
HTML5 and CSS3 content and embedded fonts.
KF8-formatted e-books are saved and distributed as MOBI files or AZW3
files, depending on the device downloading the e-book.
E-book authors can compile KF8 books using Amazon’s KingleGen software
and save them in MOBI format.
Prior to distribution, authors can preview KF8 eBooks on a Mac or PC
using Amazon’s Kindle Previewer software.
Mobipocket e-books also use the PRC extension.