Digital Rights Management (DRM) is a way to manage, and restrict, access to files. DRM is used by retailers to limit access to their products to those who have paid for them. Wikipedia has an overview of DRM including the media types affected.
Most library e-resources do not use DRM technology. Instead, you may find an access timestamp on your materials which indicates that you belong to an institution that paid for access to the materials.
Most e-Readers are restricted to only one or two types of DRM. For example, the NOOK devices use both B&N (Barnes and Noble e-books) and Adobe ID (Google Books, etc) while the Amazon Kindle devices only use AZW (Amazon Kindle ebooks). Tablets and smart phones have the advantage of having multiple apps that read different DRM types.
For a comprehensive explanation, more formats, and a table of supported devices please see the Wikipedia article Comparison of e-book formats.
Proprietary format used only with Kindle devices and applications. Usually DRM protected.
BBeB. Sony eBook format, discontinued in 2010.
Compressed folders of images. Stored using ZIP, RAR, 7z, TAR, or ACE archive types. Comic Book Archives are not a distinct file format, they are normal archives that have been given a different file extension. CBA reader applications are available for desktops, tablets and smart phones.
Most widely supported format for eBooks. DRM protected or DRM-free. Established by the International Digital Publishing Forum (IDPF) The first version was developed in 1999, EPUB 3 was approved in October 2011.
Developed by Palm Digital Media in 1996. Now uncommon. Was used by Barnes and Noble to distribute e-books but has been superseded by the ePub format.
Open XML based e-book format developed in Russia.
Flexible and extensive text formatting used by word processing programs. .doc was Microsoft Word’s default file type which in use, in various iterations, since 1983. .docx became the Microsoft Word’s default file type in 2007 replacing the .doc extension. .docx uses XML and ZIP compression resulting in significantly smaller file sizes than .doc files.
Older file format developed for smart phone mobile reading. Based on the first version of the ePub format (Open eBook). The development company was bought by Amazon in 2005. Amazon’s Kindle file format is derived from the .mobi format.
The simplest format for digital text, no formatting is supported.
Industry standard for displaying and distributing formatted text. Supports images, tables, special characters and equations.
An upgrade from Plain Text, Rich Text was developed my Microsoft in 1987 and supports limited formatting.