The Library of Congress system is very different, employing letters and numbers to organize a library's collection. We'll talk about that below. Other materials in libraries' collections include CD-ROMs, periodicals, letters, audio and video tapes, maps and gazetteers, and other materials. You just need to know how and where to look. Your key to that is the library's catalog.
Most catalogs are accessible online today through the Internet.
You can do your preliminary research without even visiting the facility and compile your list of materials in advance or determine what you might want to access via Interlibrary Loan. Consider, for instance, the county courthouses you may have visited. You can generally depend on locating land and property records with the county clerk or recorder of deeds, and wills and probate records are typically found in the office of the probate court. If you're like me, you will have found these records in some very diverse places. The same concept applies to locating obituaries, cemetery sexton records, funeral homes, pension files, immigration and naturalization records, ships passenger lists, and a huge array of other documents.