A repository is a database where the files that comprise the open textbook are stored. Some books are stored as a single PDF file. Other books are made up of a collection of files with each file containing a chapter, a learning module, an exercise, etc. When stored this way, it is easier to use a part of the book and to edit what you used.
Many of the repositories are set up and maintained by colleges and universities and made accessible via the web. Each repository has a different web interface.
Most repositories also include learning modules that are smaller or less comprehensive than a textbook suitable for a quarter, semester, or year-long course. College Open Textbook's focus is on textbooks rather than independent modules. Below is a chart of repositories recommended by the Collaborative.
|Textbooks||Courseware||K12, Free-not-open, Crowd-source|
|Connexions||OCW Consortium||Textbook Media (some open textbooks)|
|Orange Grove||NROC Hippocampus||Wikiversity/Wikibooks|
|Global Text Project||Curriki|
|Lulu (some open textbooks)|
Note that the repositories in the middle column specialize in whole courses rather than textbooks. The repositories in the right hand column feature teaching materials that might be useful in combination with textbooks but may not be acceptable as a course textbook.
Many open works are stored in more than one repository. Among those, one repository may contain the work in only one format, say a single .pdf file, while another repository may have the same work in many separate files.
A good use of the College Open Textbook's professional networks is to contact members and ask about their experience using different repositories. Also find out about the pros and cons of using open textbooks in modular files as compared to one large .pdf.