Compact Discs (CD) have many advantages. Researchers search speedily through large quantities of documents on CDs, while protecting the original materials from excessive handling. An inexpensive distribution tool, CDs hold large quantities of data in a small space. During playing, no contact occurs between the playback device and the sound carrier so wear is minimized. Many CDs incorporate an Error Detection And Correction (EDAC) system that allows reconstruction of digital data when small errors or losses occur, making perfect copying possible. Since CDs vary little over time (until they fail), they may be duplicated without generational loss of information.