Duplex systems are usually used for large volumes of records. They allow high activity files to be evenly distributed throughout the records and support the assignment of blocks of files to individuals for filing and retrieving. Decimal systems use ten general divisions, which can be subdivided by groups of ten as often as needed. The most famous decimal system is the Dewey Decimal System, developed in 1873, and used in ninety percent of the world's libraries. But they are also inflexible and limited to ten general classification areas.
Chronologic systems arrange files by date.
Alphanumeric classification uses combinations of letters and numbers. Subject-numeric systems use numbers and letters to represent subjects. A good example of a subject-numeric system is the Library of Congress classification system. Most subject-numeric systems require the use of an index. Phonetic systems are used primarily for the classification of names.