Types of repositories: institutional and subject

Institutional repositories

'An Institutional Repository is an online locus for collecting and preserving - in digital form - the intellectual output of an institution, particularly a research institution.'

'For a university, this would include materials such as research journal articles before (preprints) and after (postprints) undergoing peer review, and digital versions of theses and dissertations, but it might also include other digital assets generated by normal academic life, such as administrative documents, course notes, or learning objects.' (1)

Examples of institutional repositories include DSpace at MITe-Prints Soton at University of Southampton, and Research Online @ GCU.

Subject repositories

Also known as disciplinary (Jones, et al (2)), these are repositories based around a subject area. They can hold a variety of information including publications and objects.

Examples of subject repositories include arXivPubMed Central, and Chemistry Central.

References 
1. Wikipedia. Institutional repository, [Online] Available from: http://en.wikipedia.org/wiki/Institutional_repository [Accessed 8th August 2007]. 
2. Jones, R.; Andrew, T. & MacColl, J. The institutional repository, Chandos Publishing, Oxford, 2006 p. 6.