  Thoughtfully designing services and rigorously testing software to support
personal information management (PIM) requires understanding the relevant
collections, but relatively little is known about what people keep in their
file collections, especially personal collections. Complementing recent work on
the structure of 348 file collections, we examine those collections' contents,
how much content is duplicated, and how collections used for personal matters
differ from those used for study and work. Though all collections contain many
images, some intuitively common file types are surprisingly scarce. Personal
collections contain more audio than others, knowledge workers' collections
contain more text documents but far fewer folders, and IT collections exhibit
unusual traits. Collection duplication is correlated to collections' structural
traits, but surprisingly, not to collection age. We discuss our findings in
light of prior works and provide implications for various kinds of information
research.
