Both Discover and the Local Catalog allow you to find ebooks and printed books housed in Bizzell Memorial Library, the branch libraries, the special collections, the law library, and in storage, which includes the government documents collection. They also list all the journals, magazines, newspapers, microfilm, etc. at these locations. (Discover also lists journal articles, but the catalog does not.)
The catalog is a subset of Discover and automatically retrieves only the ebooks, books, journals, magazines, etc. in the locations mentioned above. In Discover, to see a list of only the books, you must use the filters, or, in "advanced search," limit the search to "material type" "book" before hitting search.