There are five basic types of course files for PEOI courses. The five types are
1- text course material files which include chapters, chapter sections and subsections, bibliographies, appendixes, review questions, assignments and comments
2- content files that identify and link all other files
3- cases
4- lists of courses, chapters, tables or terms, and indexes
5- questions files.

Each type is described further, and methods of accessing the files are explained below. The first three groups are HTML files, and the last two are mostly text files. Review courses may contain less than one hundred files. Professional courses have more than one thousand files.

In addition, course material files may contain images, sound or video clips, or other supporting material, all of which are highly desirable. Efforts are made to keep the size of all files small enough so that they load quickly. This also allows users to find and access wanted information rapidly. In turn, that explains the presence of a large number of files, and the need to keep track of file contents with the contents files and maintaining data banks about course pages and work performed on them.

With a few exceptions, most files are smaller than 24 KB and shorter than the equivalent of ten typed pages (including all HTML tags and scripts, but excluding images, sound or video clips). Consequently, chapters of professional courses are split into sections and sub-sections. Files containing tables with data can be especially large as a result of HTML required lay-out. Insertion of images, graphs, tables, audio and video clips is strongly recommended to bring the material to life and retain reader's attention. They obviously need a lot of space. However, they are not physically present in text files, and are accessed as resources. Special procedures are available to upload image, video and audio files, and to place links for the uploaded image or audio files.

Aside from the five types of courses files and the image or audio files that accompany them, records are kept of the location of the files, the progress made in their completion and who worked on them. The work on each file is set up as one or several tasks. The completion of the course is perceived as a project with its constituent tasks. PEOI's course development system allows planning and control of all tasks in a project.

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