Call numbers consist of a Letter (designating the general subject area in which the book belongs: R for medicine, Q for sciences, P for literature) followed by other numbers and letters which are keyed to a classification system which groups together books on a subject. Thus, a book with the call number
TK5105.875 .I57 I5 1994(The Internet Unleashed: everything you need to master the Internet) is grouped with other books on Technology (the T section);
the TKs include Electrical Engineering, Electronics and Nuclear Engineering;
TK5105 includes books about Data Transmission Systems;
TK5105.875 has to do with Special Networks and Systems;
and TK5105.875 .I57 gathers together books on the Internet.
Catalogers at the Library of Congress assign Library of Congress Subject Headings (LCSH) to books, using a system of subject categories summarized in the Big Red Books, found in the center of the circle of Annie terminals on the main level off the Leyburn Library. The 'aboutness' of a book, summarized in the SUBJECT field of a catalog record, consists of one or more LCSHs.